Embryonic stem cells

WEBVTT
Kind: captions
Language: en

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Where we left off after the
meiosis videos is that we had

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two gametes.

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We had a sperm and an egg.

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Let me draw the sperm.

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So you had the sperm and
then you had an egg.

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Maybe I'll do the egg in
a different color.

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That's the egg, and we all
know how this story goes.

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The sperm fertilizes the egg.

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And a whole cascade of events
start occurring.

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The walls of the egg then become
impervious to other

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sperm so that only one sperm can
get in, but that's not the

00:00:30.190 --> 00:00:31.120
focus of this video.

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The focus of this video is how
this fertilized egg develops

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once it has become a zygote.

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So after it's fertilized, you
remember from the meiosis

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videos that each of these were
haploid, or that they had--

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oh, I added an extra i there--
that they had half the

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contingency of the DNA.

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As soon as the sperm fertilizes
this egg, now, all

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of a sudden, you have
a diploid zygote.

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Let me do that.

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So now let me pick
a nice color.

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So now you're going to have a
diploid zygote that's going to

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have a 2N complement of the DNA
material or kind of the

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full complement of what a normal
cell in our human body

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would have. So this is diploid,
and it's a zygote,

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which is just a fancy way of
saying the fertilized egg.

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And it's now ready
to essentially

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turn into an organism.

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So immediately after
fertilization, this zygote

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starts experiencing cleavage.

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It's experiencing mitosis,
that's the mechanism, but it

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doesn't increase
a lot in size.

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So this one right here will then
turn into-- it'll just

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split up via mitosis
into two like that.

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And, of course, these are each
2N, and then those are going

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to split into four like that.

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And each of these have the same
exact genetic complement

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as that first zygote, and
it keeps splitting.

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And this mass of cells, we can
start calling it, this right

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here, this is referred
to as the morula.

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And actually, it comes from the
word for mulberry because

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it looks like a mulberry.

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So actually, let me just kind
of simplify things a little

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bit because we don't
have to start here.

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So we start with a zygote.

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This is a fertilized egg.

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It just starts duplicating via
mitosis, and you end up with a

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ball of cells.

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It's often going to be a power
of two, because these cells,

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at least in the initial stages
are all duplicating all at

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once, and then you
have this morula.

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Now, once the morula gets to
about 16 cells or so-- and

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we're talking about
four or five days.

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This isn't an exact process--
they started differentiating a

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little bit, where the outer
cells-- and this kind of turns

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into a sphere.

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Let me make it a little
bit more sphere like.

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So it starts differentiating
between-- let me make some

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outer cells.

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This would be a cross-section
of it.

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It's really going to look
more like a sphere.

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That's the outer cells and then
you have your inner cells

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on the inside.

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These outer cells are called
the trophoblasts.

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Let me do it in a
different color.

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Let me scroll over.

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I don't want to go there.

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And then the inner cells, and
this is kind of the crux of

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what this video is all
about-- let me scroll

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down a little bit.

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The inner cells-- pick
a suitable color.

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The inner cells right there are
called the embryoblast.

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And then what's going to happen
is some fluid's going

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to start filling in some
of this gap between the

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embryoblast and the trophoblast,
so you're going

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to start having some fluid that
comes in there, and so

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the morula will eventually
look like this, where the

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trophoblast, or the outer
membrane, is kind of this huge

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sphere of cells.

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And this is all happening as
they keep replicating.

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Mitosis is the mechanism, so now
my trophoblast is going to

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look like that, and then
my embryoblast is going

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to look like this.

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Sometimes the embryoblast-- so
this is the embryoblast.

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Sometimes it's also called the
inner cell mass, so let me

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write that.

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And this is what's going to
turn into the organism.

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And so, just so you know a
couple of the labels that are

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involved here, if we're dealing
with a mammalian

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organism, and we are mammals,
we call this thing that the

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morula turned into is a zygote,
then a morula, then

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the cells of the morula started
to differentiate into

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the trophoblast, or kind of the
outside cells, and then

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the embryoblast. And then you
have this space that forms

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here, and this is just fluid,
and it's called the

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blastocoel.

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A very non-intuitive spelling
of the coel part of

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blastocoel.

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But once this is formed, this is
called a blastocyst. That's

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the entire thing right here.

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Let me scroll down
a little bit.

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This whole thing is called the
blastocyst, and this is the

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case in humans.

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Now, it can be a very confusing
topic, because a lot

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of times in a lot of books on
biology, you'll say, hey, you

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go from the morula to
the blastula or the

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blastosphere stage.

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Let me write those words down.

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So sometimes you'll say morula,

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and you go to blastula.

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Sometimes it's called
the blastosphere.

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And I want to make it very
clear that these are

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essentially the same stages
in development.

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These are just for-- you know,
in a lot of books, they'll

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start talking about frogs or
tadpoles or things like that,

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and this applies to them.

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While we're talking about
mammals, especially the ones

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that are closely related
to us, the stage is the

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blastocyst stage, and the real
differentiator is when people

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talk about just blastula
and blastospheres.

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There isn't necessarily this
differentiation between these

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outermost cells and these
embryonic, or this

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embryoblast, or this inner
cell mass here.

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But since the focus of this
video is humans, and really

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that's where I wanted to start
from, because that's what we

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are and that's what's
interesting, we're going to

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focus on the blastocyst.

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Now, everything I've talked
about in this video, it was

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really to get to this point,
because what we have here,

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these little green cells that
I drew right here in the

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blastocysts, this inner cell
mass, this is what will turn

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into the organism.

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And you say, OK, Sal, if that's
the organism, what's

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all of these purple
cells out here?

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This trophoblast out there?

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That is going to turn into the
placenta, and I'll do a future

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video where in a human, it'll
turn into a placenta.

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So let me write that down.

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It'll turn into the placenta.

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And I'll do a whole future video
about I guess how babies

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are born, and I actually learned
a ton about that this

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past year because a baby
was born in our house.

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But the placenta is really
kind of what the embryo

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develops inside of, and it's the
interface, especially in

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humans and in mammals, between
the developing fetus and its

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mother, so it kind of is the
exchange mechanism that

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separates their two systems,
but allows the necessary

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functions to go on
between them.

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But that's not the focus
of this video.

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The focus of this video is the
fact that these cells, which

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at this point are-- they've
differentiated themselves away

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from the placenta cells, but
they still haven't decided

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what they're going to become.

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Maybe this cell and its
descendants eventually start

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becoming part of the nervous
system, while these cells

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right here might become muscle
tissue, while these cells

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right here might become
the liver.

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These cells right here are
called embryonic stem cells,

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and probably the first time in
this video you're hearing a

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term that you might recognize.

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So if I were to just take one of
these cells, and actually,

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just to introduce you to another
term, you know, we

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have this zygote.

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As soon as it starts dividing,
each of these cells are called

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a blastomere.

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And you're probably wondering,
Sal, why does this word blast

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keep appearing in this kind
of embryology video, these

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development videos?

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And that comes from the Greek
for spore: blastos.

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So the organism is beginning
to spore out or grow.

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I won't go into the word origins
of it, but that's

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where it comes from and that's
why everything has

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this blast in it.

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So these are blastomeres.

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So when I talk what embryonic
stem cells, I'm talking about

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the individual blastomeres
inside of this embryoblast or

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inside of this inner
cell mass.

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These words are actually
unusually fun to say.

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So each of these is an
embryonic stem cell.

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Let me write this down
in a vibrant color.

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So each of these right here are
embryonic stem cells, and

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I wanted to get to this.

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And the reason why these are
interesting, and I think you

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already know, is that there's
a huge debate around these.

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One, these have the potential
to turn into anything, that

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they have this plasticity.

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That's another word that
you might hear.

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Let me write that down,
too: plasticity.

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And the word essentially comes
from, you know, like a plastic

00:10:14.920 --> 00:10:17.130
can turn into anything else.

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When we say that something has
plasticity, we're talking

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about its potential
to turn into a lot

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of different things.

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So the theory is, and there's
already some trials that seem

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to substantiate this, especially
in some lower

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organisms, that, look, if you
have some damage at some point

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in your body-- let me
draw a nerve cell.

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Let me say I have a-- I won't
go into the actual mechanics

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of a nerve cell, but let's say
that we have some damage at

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some point on a nerve cell right
there, and because of

00:10:46.980 --> 00:10:50.450
that, someone is paralyzed
or there's some nerve

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dysfunction.

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We're dealing with multiple
sclerosis or who knows what.

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The idea is, look, we have these
cell here that could

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turn into anything, and we're
just really understanding how

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it knows what to turn into.

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It really has to look at its
environment and say, hey, what

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are the guys around me doing,
and maybe that's what helps

00:11:08.900 --> 00:11:10.150
dictate what it does.

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But the idea is you take these
things that could turn to

00:11:12.500 --> 00:11:16.740
anything and you put them where
the damage is, you layer

00:11:16.740 --> 00:11:19.910
them where the damage is, and
then they can turn into the

00:11:19.910 --> 00:11:21.510
cell that they need
to turn into.

00:11:21.510 --> 00:11:24.990
So in this case, they would
turn into nerve cells.

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They would turn to nerve cells
and repair the damage and

00:11:29.220 --> 00:11:32.480
maybe cure the paralysis
for that individual.

00:11:32.480 --> 00:11:35.640
So it's a huge, exciting area
of research, and you could

00:11:35.640 --> 00:11:37.700
even, in theory, grow
new organs.

00:11:37.700 --> 00:11:39.800
If someone needs a kidney
transplant or a heart

00:11:39.800 --> 00:11:43.690
transplant, maybe in the future,
we could take a colony

00:11:43.690 --> 00:11:44.980
of these embryonic stem cells.

00:11:44.980 --> 00:11:48.510
Maybe we can put them in some
type of other creature, or who

00:11:48.510 --> 00:11:52.050
knows what, and we can turn it
into a replacement heart or a

00:11:52.050 --> 00:11:52.660
replacement kidney.

00:11:52.660 --> 00:11:56.480
So there's a huge amount
of excitement about

00:11:56.480 --> 00:11:57.420
what these can do.

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I mean, they could cure a lot of
formerly uncurable diseases

00:12:01.310 --> 00:12:03.350
or provide hope for a
lot of patients who

00:12:03.350 --> 00:12:05.120
might otherwise die.

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But obviously, there's
a debate here.

00:12:07.870 --> 00:12:10.950
And the debate all revolves
around the issue of if you

00:12:10.950 --> 00:12:15.120
were to go in here and try to
extract one of these cells,

00:12:15.120 --> 00:12:17.560
you're going to kill
this embryo.

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You're going to kill this
developing embryo, and that

00:12:21.160 --> 00:12:23.670
developing embryo had
the potential to

00:12:23.670 --> 00:12:27.140
become a human being.

00:12:27.140 --> 00:12:28.880
It's a potential that obviously
has to be in the

00:12:28.880 --> 00:12:33.520
right environment, and it has
to have a willing mother and

00:12:33.520 --> 00:12:35.820
all of the rest, but it does
have the potential.

00:12:35.820 --> 00:12:40.370
And so for those, especially, I
think, in the pro-life camp,

00:12:40.370 --> 00:12:44.280
who say, hey, anything that has
a potential to be a human

00:12:44.280 --> 00:12:47.310
being, that is life and it
should not be killed.

00:12:47.310 --> 00:12:52.510
So people on that side of the
camp, they're against the

00:12:52.510 --> 00:12:54.510
destroying of this embryo.

00:12:54.510 --> 00:12:57.880
I'm not making this video to
take either side to that

00:12:57.880 --> 00:13:01.740
argument, but it's a potential
to turn to a human being.

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It's a potential, right?

00:13:04.010 --> 00:13:07.730
So obviously, there's a huge
amount of debate, but now, now

00:13:07.730 --> 00:13:10.310
you know in this video what
people are talking about when

00:13:10.310 --> 00:13:12.690
they say embryonic stem cells.

00:13:12.690 --> 00:13:14.680
And obviously, the next question
is, hey, well, why

00:13:14.680 --> 00:13:16.910
don't they just call them stem
cells as opposed to embryonic

00:13:16.910 --> 00:13:17.490
stem cells?

00:13:17.490 --> 00:13:20.875
And that's because in all of our
bodies, you do have what

00:13:20.875 --> 00:13:22.850
are called somatic stem cells.

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Let me write that down.

00:13:24.850 --> 00:13:29.000
Somatic or adults stem cells.

00:13:29.000 --> 00:13:30.100
And we all have them.

00:13:30.100 --> 00:13:32.860
They're in our bone marrow to
help produce red blood cells,

00:13:32.860 --> 00:13:36.160
other parts of our body, but the
problem with somatic stem

00:13:36.160 --> 00:13:41.780
cells is they're not as plastic,
which means that they

00:13:41.780 --> 00:13:44.810
can't form any type of cell
in the human body.

00:13:44.810 --> 00:13:46.880
There's an area of research
where people are actually

00:13:46.880 --> 00:13:50.470
maybe trying to make them more
plastic, and if they are able

00:13:50.470 --> 00:13:52.900
to take these somatic stem
cells and make them more

00:13:52.900 --> 00:13:56.290
plastic, it might maybe kill
the need to have these

00:13:56.290 --> 00:13:58.660
embryonic stem cells, although
maybe if they do this too

00:13:58.660 --> 00:14:01.690
good, maybe these will have
the potential to turn into

00:14:01.690 --> 00:14:03.010
human beings as well,
so that could

00:14:03.010 --> 00:14:04.770
become a debatable issue.

00:14:04.770 --> 00:14:08.130
But right now, this isn't an
area of debate because, left

00:14:08.130 --> 00:14:12.510
to their own devices, a somatic
stem cell or an adult

00:14:12.510 --> 00:14:15.420
stem cell won't turn into
a human being, while an

00:14:15.420 --> 00:14:19.760
embryonic one, if it is
implanted in a willing mother,

00:14:19.760 --> 00:14:21.970
then, of course, it will turn
into a human being.

00:14:21.970 --> 00:14:24.210
And I want to make one side
note here, because I don't

00:14:24.210 --> 00:14:30.410
want to take any sides on the
debate of-- well, I mean,

00:14:30.410 --> 00:14:31.250
facts are facts.

00:14:31.250 --> 00:14:33.900
This does have the potential
to turn into a human being,

00:14:33.900 --> 00:14:36.980
but it also has the potential
to save millions of lives.

00:14:36.980 --> 00:14:39.740
Both of those statements are
facts, and then you can decide

00:14:39.740 --> 00:14:42.960
on your own which side of that
argument you'd like to or what

00:14:42.960 --> 00:14:45.670
side of that balance you
would like to kind of

00:14:45.670 --> 00:14:47.210
put your own opinion.

00:14:47.210 --> 00:14:50.020
But there's one thing I want
to talk about that in the

00:14:50.020 --> 00:14:51.890
public debate is never
brought up.

00:14:51.890 --> 00:14:55.600
So you have this notion of when
you-- to get an embryonic

00:14:55.600 --> 00:14:58.570
stem cell line, and when I say
a stem cell line, I mean you

00:14:58.570 --> 00:15:00.880
take a couple of stem cells, or
let's say you take one stem

00:15:00.880 --> 00:15:04.550
cell, and then you put it in a
Petri dish, and then you allow

00:15:04.550 --> 00:15:06.650
it to just duplicate.

00:15:06.650 --> 00:15:09.780
So this one turns into two,
those two turn to four.

00:15:09.780 --> 00:15:12.380
Then someone could take one of
these and then put it in their

00:15:12.380 --> 00:15:13.600
own Petri dish.

00:15:13.600 --> 00:15:15.200
These are a stem cell line.

00:15:15.200 --> 00:15:20.310
They all came from one unique
embryonic stem cell or what

00:15:20.310 --> 00:15:21.950
initially was a blastomere.

00:15:21.950 --> 00:15:24.500
So that's what they call
a stem cell line.

00:15:24.500 --> 00:15:28.140
So the debate obviously is when
you start an embryonic

00:15:28.140 --> 00:15:31.060
stem cell line, you are
destroying an embryo.

00:15:31.060 --> 00:15:33.900
But I want to make the point
here that embryos are being

00:15:33.900 --> 00:15:37.140
destroyed in other processes,
and namely, in-vitro

00:15:37.140 --> 00:15:38.390
fertilization.

00:15:40.530 --> 00:15:44.740
And maybe this'll be my next
video: fertilization.

00:15:44.740 --> 00:15:48.690
And this is just the notion that
they take a set of eggs

00:15:48.690 --> 00:15:49.515
out of a mother.

00:15:49.515 --> 00:15:52.430
It's usually a couple that's
having trouble having a child,

00:15:52.430 --> 00:15:54.280
and they take a bunch of
eggs out of the mother.

00:15:54.280 --> 00:15:56.940
So let's say they take
maybe 10 to 30

00:15:56.940 --> 00:15:59.000
eggs out of the mother.

00:15:59.000 --> 00:16:02.460
They actually perform a surgery,
take them out of the

00:16:02.460 --> 00:16:06.760
ovaries of the mother, and then
they fertilize them with

00:16:06.760 --> 00:16:09.890
semen, either it might come
from the father or a sperm

00:16:09.890 --> 00:16:13.210
donor, so then all of these
becomes zygotes once they're

00:16:13.210 --> 00:16:15.090
fertilized with semen.

00:16:15.090 --> 00:16:17.860
So these all become zygotes,
and then they allow them to

00:16:17.860 --> 00:16:19.870
develop, and they usually allow
them to develop to the

00:16:19.870 --> 00:16:21.480
blastocyst stage.

00:16:21.480 --> 00:16:25.600
So eventually all of these
turn into blastocysts.

00:16:25.600 --> 00:16:30.050
They have a blastocoel in
the center, which is

00:16:30.050 --> 00:16:32.520
this area of fluid.

00:16:32.520 --> 00:16:37.920
They have, of course, the
embryo, the inner cell mass in

00:16:37.920 --> 00:16:41.310
them, and what they do is they
look at the ones that they

00:16:41.310 --> 00:16:44.180
deem are healthier or maybe
the ones that are at least

00:16:44.180 --> 00:16:47.400
just not unhealthy, and they'll
take a couple of these

00:16:47.400 --> 00:16:50.160
and they'll implant these into
the mother, so all of this is

00:16:50.160 --> 00:16:52.180
occurring in a Petri dish.

00:16:52.180 --> 00:16:55.270
So maybe these four look good,
so they're going to take these

00:16:55.270 --> 00:16:57.840
four, and they're going to
implant these into a mother,

00:16:57.840 --> 00:17:01.070
and if all goes well, maybe one
of these will turn into--

00:17:01.070 --> 00:17:02.670
will give the couple a child.

00:17:02.670 --> 00:17:05.180
So this one will develop and
maybe the other ones won't.

00:17:05.180 --> 00:17:09.520
But if you've seen John & Kate
Plus 8, you know that many

00:17:09.520 --> 00:17:12.349
times they implant a lot of
them in there, just to

00:17:12.349 --> 00:17:14.520
increase the probability that
you get at least one child.

00:17:14.520 --> 00:17:17.310
But every now and then, they
implant seven or eight, and

00:17:17.310 --> 00:17:18.680
then you end up with
eight kids.

00:17:18.680 --> 00:17:21.150
And that's why in-vitro
fertilization often results in

00:17:21.150 --> 00:17:25.359
kind of these multiple
births, or reality

00:17:25.359 --> 00:17:27.270
television shows on cable.

00:17:27.270 --> 00:17:30.330
But what do they do with all
of these other perfectly--

00:17:30.330 --> 00:17:33.110
well, I won't say perfectly
viable, but these are embryos.

00:17:33.110 --> 00:17:36.350
They may or may not be perfectly
viable, but you have

00:17:36.350 --> 00:17:41.980
these embryos that have the
potential, just like this one

00:17:41.980 --> 00:17:42.680
right here.

00:17:42.680 --> 00:17:46.340
These all have the potential
to turn into a human being.

00:17:46.340 --> 00:17:50.730
But most fertility clinics,
roughly half of them, they

00:17:50.730 --> 00:17:52.950
either throw these away,
they destroy them, they

00:17:52.950 --> 00:17:54.040
allow them to die.

00:17:54.040 --> 00:17:56.690
A lot of these are frozen, but
just the process of freezing

00:17:56.690 --> 00:17:59.370
them kills them and then bonding
them kills them again,

00:17:59.370 --> 00:18:04.290
so most of these, the process of
in-vitro fertilization, for

00:18:04.290 --> 00:18:08.740
every one child that has the
potential to develop into a

00:18:08.740 --> 00:18:10.500
full-fledged human being, you're
actually destroying

00:18:10.500 --> 00:18:14.730
tens of very viable embryos.

00:18:14.730 --> 00:18:18.550
So at least my take on it is
if you're against-- and I

00:18:18.550 --> 00:18:21.750
generally don't want to take a
side on this, but if you are

00:18:21.750 --> 00:18:33.320
against research that involves
embryonic stem cells because

00:18:33.320 --> 00:18:36.580
of the destruction of embryos,
on that same, I guess,

00:18:36.580 --> 00:18:40.630
philosophical ground, you
should also be against

00:18:40.630 --> 00:18:47.360
in-vitro fertilization because
both of these involve the

00:18:47.360 --> 00:18:49.540
destruction of zygotes.

00:18:49.540 --> 00:18:52.520
I think-- well, I won't talk
more about this, because I

00:18:52.520 --> 00:18:54.320
really don't want to take sides,
but I want to show that

00:18:54.320 --> 00:18:56.850
there is kind of an equivalence
here that's

00:18:56.850 --> 00:19:00.755
completely lost in this debate
on whether embryonic stem

00:19:00.755 --> 00:19:02.920
cells should be used because
they have a destruction of

00:19:02.920 --> 00:19:04.980
embryos, because you're
destroying just as many

00:19:04.980 --> 00:19:08.000
embryos in this-- well, I won't
say just as many, but

00:19:08.000 --> 00:19:09.580
you are destroying embryos.

00:19:09.580 --> 00:19:12.720
There's hundreds of thousands of
embryos that get destroyed

00:19:12.720 --> 00:19:16.210
and get frozen and obviously
destroyed in that process as

00:19:16.210 --> 00:19:19.120
well through this in-vitro
fertilization process.

00:19:19.120 --> 00:19:22.010
So anyway, now hopefully you
have the tools to kind of

00:19:22.010 --> 00:19:25.140
engage in the debate around stem
cells, and you see that

00:19:25.140 --> 00:19:29.870
it all comes from what we
learned about meiosis.

00:19:29.870 --> 00:19:33.200
They produce these gametes.

00:19:33.200 --> 00:19:35.790
The male gamete fertilizes
a female gamete.

00:19:35.790 --> 00:19:39.510
The zygote happens or gets
created and starts splitting

00:19:39.510 --> 00:19:42.490
up the morula, and then it
keeps splitting and it

00:19:42.490 --> 00:19:45.730
differentiates into the
blastocyst, and then this is

00:19:45.730 --> 00:19:47.230
where the stem cells are.

00:19:47.230 --> 00:19:50.320
So you already know enough
science to engage in kind of a

00:19:50.320 --> 00:19:53.770
very heated debate.


Cancer

WEBVTT
Kind: captions
Language: en

00:00:00.000 --> 00:00:03.400
Most cells in the human body
just go about their business

00:00:03.400 --> 00:00:06.320
on a daily basis in a fairly
respectable way.

00:00:06.320 --> 00:00:07.960
Let's say that I have
some cell here.

00:00:07.960 --> 00:00:12.250
This could be maybe a skin cell
or really any cell in any

00:00:12.250 --> 00:00:13.480
tissue in the body.

00:00:13.480 --> 00:00:18.370
As that tissue is growing or
it's replacing dead cells, the

00:00:18.370 --> 00:00:21.080
cells will experience mitosis
and replicate themselves, make

00:00:21.080 --> 00:00:22.330
perfect copies of each other.

00:00:22.330 --> 00:00:25.680
And then those two maybe will
experience mitosis, and then

00:00:25.680 --> 00:00:27.590
if they realize that, gee, you
know, it's getting a little

00:00:27.590 --> 00:00:29.330
bit crowded.

00:00:29.330 --> 00:00:30.840
There are other cells
in my neighborhood.

00:00:35.310 --> 00:00:36.880
They'll recognize that, and say,
you know, I'm going to

00:00:36.880 --> 00:00:38.190
stop growing a little bit.

00:00:38.190 --> 00:00:39.560
That's called contact
inhibition.

00:00:43.000 --> 00:00:44.290
And so they'll just
start growing.

00:00:44.290 --> 00:00:49.670
And then let's say one of them
experiences a little defect,

00:00:49.670 --> 00:00:53.800
and he says, you know what, gee,
something's a little bit

00:00:53.800 --> 00:00:54.730
wrong with me.

00:00:54.730 --> 00:00:58.270
I, the cell, recognize this in
myself, and the cells will

00:00:58.270 --> 00:00:59.250
actually kill themselves.

00:00:59.250 --> 00:01:02.770
That's how good of cellular
citizens they are.

00:01:02.770 --> 00:01:07.060
They'll kind of make way for
other healthy cells.

00:01:07.060 --> 00:01:09.840
So this guy might even kill
himself if he realizes that

00:01:09.840 --> 00:01:10.920
there's something
wrong with him.

00:01:10.920 --> 00:01:13.110
There's actually a cellular
mechanism that does that

00:01:13.110 --> 00:01:15.170
called apoptosis.

00:01:15.170 --> 00:01:16.255
And I want to make
this very clear.

00:01:16.255 --> 00:01:19.540
This isn't some type of outside
influence on the cell.

00:01:19.540 --> 00:01:22.860
The cell itself recognizes that
it's somehow damaged and

00:01:22.860 --> 00:01:26.550
it just destroys itself,
so apoptosis.

00:01:26.550 --> 00:01:28.870
So that's the regular
circumstance even when there

00:01:28.870 --> 00:01:30.000
is a mutation.

00:01:30.000 --> 00:01:32.590
And just to give you an idea,
even if mutations are

00:01:32.590 --> 00:01:33.880
relatively infrequent.

00:01:33.880 --> 00:01:35.780
And I don't know the exact
frequencies at

00:01:35.780 --> 00:01:36.940
which mutations occur.

00:01:36.940 --> 00:01:39.780
I suspect it's of different
frequencies in different types

00:01:39.780 --> 00:01:40.640
of tissues.

00:01:40.640 --> 00:01:46.000
There are on the order
of 100 billion.

00:01:46.000 --> 00:01:47.830
Let me do it in a
different color.

00:01:47.830 --> 00:01:54.160
There are on the order of 100
billion new cells in the human

00:01:54.160 --> 00:01:57.750
body per day.

00:01:57.750 --> 00:02:01.280
So even if a mutation only
occurs one in a million times,

00:02:01.280 --> 00:02:05.860
you're still dealing with
roughly 100,000 mutations, and

00:02:05.860 --> 00:02:09.169
maybe most of the mutations,
maybe they're just some little

00:02:09.169 --> 00:02:11.980
random things that don't
really do a lot.

00:02:11.980 --> 00:02:13.990
But if the mutations are a
little bit more severe, the

00:02:13.990 --> 00:02:16.480
cell will recognize it
and destroy itself.

00:02:16.480 --> 00:02:18.890
And I want to make a very
clear point here.

00:02:18.890 --> 00:02:23.510
I'm talking about the cells of
the body or most of the body.

00:02:23.510 --> 00:02:27.900
This could be the cells in my
eye or the cells in my brain

00:02:27.900 --> 00:02:30.710
or the cells on my leg.

00:02:30.710 --> 00:02:32.100
These aren't my germ cells.

00:02:32.100 --> 00:02:35.430
So these mutations, even if the
cell survives, will not be

00:02:35.430 --> 00:02:37.260
passed on to my offspring.

00:02:37.260 --> 00:02:39.390
That's an entirely different
discussion when

00:02:39.390 --> 00:02:41.100
we talk about meiosis.

00:02:41.100 --> 00:02:44.260
These are all my body cells and
they're replicating, and

00:02:44.260 --> 00:02:48.500
we've gone over this
with mitosis.

00:02:48.500 --> 00:02:51.480
So any mutations here, they'll
either do nothing, or the

00:02:51.480 --> 00:02:54.590
cells might malfunction a little
bit, or the cells might

00:02:54.590 --> 00:02:57.020
hurt themselves or hurt me,
but they're not going to

00:02:57.020 --> 00:02:58.430
affect my offspring.

00:02:58.430 --> 00:03:00.230
And I want to make that
point very clear.

00:03:00.230 --> 00:03:04.390
Now, you're saying, hey, Sal,
100 billion new cells a day?

00:03:04.390 --> 00:03:07.780
That must mean like every cell
in my body has created, well

00:03:07.780 --> 00:03:09.830
that just gives you an idea of
how many cells we have. We

00:03:09.830 --> 00:03:13.170
actually have on the order of,
and you know it's obviously

00:03:13.170 --> 00:03:16.010
not an exact number, but
actually in the human body,

00:03:16.010 --> 00:03:22.940
there's on the order of
100 trillion cells.

00:03:22.940 --> 00:03:25.610
And if you look at it that way,
you say on average, one

00:03:25.610 --> 00:03:28.600
thousandth of your cells
replicate each day, but the

00:03:28.600 --> 00:03:31.700
reality is some cells don't
replicate that frequently at

00:03:31.700 --> 00:03:35.950
all and some cells replicate
much more frequently.

00:03:35.950 --> 00:03:38.480
Just to take a little side note
here, this gives you an

00:03:38.480 --> 00:03:42.040
appreciation, I think, for the
complexity of the human body.

00:03:42.040 --> 00:03:45.940
I mean we think of our own
world economy and world

00:03:45.940 --> 00:03:49.470
society as so complex, it's made
up of 6 billion humans.

00:03:49.470 --> 00:03:53.460
We're made up of 100
trillion cells.

00:03:53.460 --> 00:03:55.780
Let me rewrite 100 trillion
in billions.

00:03:55.780 --> 00:04:03.560
100 trillion can be rewritten
as 100,000 billion cells.

00:04:03.560 --> 00:04:09.440
And each one of those 100,000
billion cells are these huge--

00:04:09.440 --> 00:04:12.010
I know I shouldn't use the word
huge-- but they're these

00:04:12.010 --> 00:04:15.890
complex ecosystems in and of

00:04:15.890 --> 00:04:17.959
themselves with their nucleuses.

00:04:17.959 --> 00:04:20.110
And we'll talk about all the
different organelles they

00:04:20.110 --> 00:04:23.120
have, and we talked about
cellular replication, DNA

00:04:23.120 --> 00:04:25.140
replication and how the
cell replicates.

00:04:25.140 --> 00:04:28.190
So these things aren't jokes
and they have all of these

00:04:28.190 --> 00:04:31.580
complex membranes that take
things into them.

00:04:31.580 --> 00:04:34.150
They are creatures to
themselves, but they live in

00:04:34.150 --> 00:04:39.550
this complex environment or
society that is each of us.

00:04:39.550 --> 00:04:42.020
So that's just a side note just
to appreciate how large

00:04:42.020 --> 00:04:43.790
and how complex we are.

00:04:43.790 --> 00:04:47.030
But you can imagine, and this
is how I got off on this

00:04:47.030 --> 00:04:51.090
tangent, if we're making on the
order of 100 billion new

00:04:51.090 --> 00:04:54.140
cells every day, you're going
to have a lot of mutations,

00:04:54.140 --> 00:04:56.820
and maybe some of the mutations,
you know I said

00:04:56.820 --> 00:04:58.030
some of them don't
do anything.

00:04:58.030 --> 00:05:00.530
Some of them, the cell
recognizes that the cell is

00:05:00.530 --> 00:05:05.140
just going to be kind of dead
weight so the cell kind of

00:05:05.140 --> 00:05:06.240
eliminates itself.

00:05:06.240 --> 00:05:08.370
But every now and then, you have
mutations where the cell

00:05:08.370 --> 00:05:13.220
doesn't eliminate itself and
it also deforms the cell.

00:05:13.220 --> 00:05:16.780
So when you have that, let's
say I have some cell here.

00:05:16.780 --> 00:05:20.280
I have some cell and it's
got some mutation.

00:05:20.280 --> 00:05:27.320
I'll do that mutation with
a little x right here.

00:05:27.320 --> 00:05:28.550
That's in its DNA.

00:05:28.550 --> 00:05:30.180
Maybe it's got a couple
of mutations.

00:05:30.180 --> 00:05:32.510
So one of the mutations keeps
it from experiencing

00:05:32.510 --> 00:05:35.460
apoptosis, or destroying itself,
and maybe one of the

00:05:35.460 --> 00:05:37.090
mutations makes it replicate
a little bit

00:05:37.090 --> 00:05:38.610
faster than its neighbors.

00:05:38.610 --> 00:05:43.340
So this cell, through mitosis,
it makes a bunch of copies of

00:05:43.340 --> 00:05:48.130
itself or a ton of
copies of itself.

00:05:48.130 --> 00:05:54.490
And this kind of body of cells
that essentially has a defect,

00:05:54.490 --> 00:05:58.060
they're all from one original
cell that kept duplicating and

00:05:58.060 --> 00:06:01.050
then those duplicating, but all
these are defective cells.

00:06:01.050 --> 00:06:05.910
If you were to look at them
compared to the tissue around

00:06:05.910 --> 00:06:07.870
it, it would look abnormal
in some way.

00:06:07.870 --> 00:06:09.850
Maybe it wouldn't function
properly.

00:06:09.850 --> 00:06:11.100
This is called a neoplasm.

00:06:17.890 --> 00:06:20.910
Now, a lot of neoplasms,
well they don't have to

00:06:20.910 --> 00:06:21.910
form a body like this.

00:06:21.910 --> 00:06:24.570
Sometimes they might somehow
circulate in the body, but

00:06:24.570 --> 00:06:28.200
most of the time they form
this kind of big lump.

00:06:28.200 --> 00:06:30.080
And if they get large enough,
they're noticeable.

00:06:30.080 --> 00:06:32.230
And that's when we
call it a tumor.

00:06:32.230 --> 00:06:37.990
So if this is actually a lump
of kind of differentiated

00:06:37.990 --> 00:06:40.290
tissue that's definitely
abnormal, that's

00:06:40.290 --> 00:06:41.730
what you call a tumor.

00:06:41.730 --> 00:06:45.360
So the term neoplasm and
tumor are often used

00:06:45.360 --> 00:06:46.070
interchangeably.

00:06:46.070 --> 00:06:50.900
Tumor is the word we use more
in our everyday vocabulary.

00:06:50.900 --> 00:06:55.900
Now, if this lump just kind of
grows to a certain size, it's

00:06:55.900 --> 00:06:58.640
just there, it doesn't really
do anything dangerous, it's

00:06:58.640 --> 00:07:02.470
not replicating out
of control.

00:07:02.470 --> 00:07:04.380
I guess it's not replicating
a lot faster than its

00:07:04.380 --> 00:07:06.690
neighboring cells and it's
just hanging out, maybe

00:07:06.690 --> 00:07:10.340
growing a little bit, but not in
any significant way harming

00:07:10.340 --> 00:07:13.340
our environment, we
call that a benign

00:07:13.340 --> 00:07:14.780
tumor or a benign neoplasm.

00:07:17.420 --> 00:07:19.530
And benign essentially
means harmless.

00:07:19.530 --> 00:07:21.155
Benign tumor.

00:07:21.155 --> 00:07:23.810
That means that's good.

00:07:23.810 --> 00:07:24.610
You want to hear that.

00:07:24.610 --> 00:07:28.380
If you got a lump-- God forbid
you have a lump either way--

00:07:28.380 --> 00:07:30.990
but if you do and it's a benign
tumor, that means that

00:07:30.990 --> 00:07:33.690
lump, it can kind of stick
around, no damage done.

00:07:33.690 --> 00:07:38.400
But if these DNA mutations, and
maybe some of these are,

00:07:38.400 --> 00:07:41.400
it is benign, but maybe one of
the benign ones has another

00:07:41.400 --> 00:07:45.255
mutation in it that starts
making it grow like crazy.

00:07:48.510 --> 00:07:50.320
And not only does it
grow like crazy,

00:07:50.320 --> 00:07:51.776
but it becomes invasive.

00:07:51.776 --> 00:07:55.330
And invasive means that
it doesn't care what's

00:07:55.330 --> 00:07:56.630
going on around it.

00:07:56.630 --> 00:07:58.480
It just wants to infiltrate
everything.

00:07:58.480 --> 00:08:02.080
So let's say that guy
grows like crazy.

00:08:02.080 --> 00:08:03.430
Let me do it in a
different color.

00:08:03.430 --> 00:08:05.700
And he starts infiltrating
other

00:08:05.700 --> 00:08:10.280
tissue, so he's invasive.

00:08:10.280 --> 00:08:15.810
So super growth,
he's invasive.

00:08:15.810 --> 00:08:17.560
So he doesn't care
what's going on.

00:08:17.560 --> 00:08:20.430
He's all of a sudden turned into
some type of a cellular

00:08:20.430 --> 00:08:21.420
psychopath.

00:08:21.420 --> 00:08:23.550
And even worse, his descendants,
it's not just one

00:08:23.550 --> 00:08:23.980
cell anymore.

00:08:23.980 --> 00:08:28.520
He just keeps duplicating and
passing on this kind of broken

00:08:28.520 --> 00:08:30.760
genetic information that makes
it want to replicate.

00:08:30.760 --> 00:08:36.610
And then maybe there could be
more and more things that

00:08:36.610 --> 00:08:41.520
break down in its I guess
offspring or the DNA that

00:08:41.520 --> 00:08:43.130
comes from its replications.

00:08:43.130 --> 00:08:46.390
And actually, that's a good
likelihood, because the same

00:08:46.390 --> 00:08:50.730
parts of its DNA that broke
down, some of the DNA that

00:08:50.730 --> 00:08:53.060
broke down in this guy, some
of the mutations might have

00:08:53.060 --> 00:08:56.040
actually hurt the DNA
replication scheme, so that

00:08:56.040 --> 00:08:58.240
mutations become
more frequent.

00:08:58.240 --> 00:09:02.660
So more frequent mutations.

00:09:02.660 --> 00:09:06.340
So as these replicate, more and
more mutations appear, and

00:09:06.340 --> 00:09:08.710
then maybe eventually one of
the mutations appears that

00:09:08.710 --> 00:09:13.010
allows these cells to break off
and then travel to other

00:09:13.010 --> 00:09:14.260
parts of the body.

00:09:16.730 --> 00:09:19.320
And then those parts of the body
start to take over and

00:09:19.320 --> 00:09:21.190
start taking over all
of the cells.

00:09:21.190 --> 00:09:25.500
And this process is called the
cell has-- this is one of the

00:09:25.500 --> 00:09:27.770
hardest words for me to say,
something wrong with my

00:09:27.770 --> 00:09:30.970
brain-- but the cell
has metastasized.

00:09:35.850 --> 00:09:38.710
You might have heard the word
metastasis, and that's just

00:09:38.710 --> 00:09:42.470
the notion of these run amok
cells all of a sudden being

00:09:42.470 --> 00:09:44.810
able to travel to different
parts of the body.

00:09:44.810 --> 00:09:47.790
And I think you guys know what
we call these cells.

00:09:47.790 --> 00:09:49.890
These cells that aren't
respecting their cellular

00:09:49.890 --> 00:09:50.310
neighborhood.

00:09:50.310 --> 00:09:52.960
They're growing like crazy.

00:09:52.960 --> 00:09:55.690
They don't experience that
contact inhibition.

00:09:55.690 --> 00:09:56.940
They're invasive.

00:09:56.940 --> 00:10:00.580
They start crowding out
other cells and

00:10:00.580 --> 00:10:02.040
hogging up the resources.

00:10:02.040 --> 00:10:04.290
And they keep mutating really
fast because they have all of

00:10:04.290 --> 00:10:06.050
these genetic abnormalities.

00:10:06.050 --> 00:10:08.150
And eventually they might even
break away and start

00:10:08.150 --> 00:10:09.940
infiltrating other parts
of the body.

00:10:09.940 --> 00:10:12.985
These are cancers
or cancer cells.

00:10:15.620 --> 00:10:17.100
And so you might have
an appreciation for

00:10:17.100 --> 00:10:19.100
why this is so hard.

00:10:19.100 --> 00:10:24.240
Cancer is such a hard disease
to quote, unquote, cure.

00:10:24.240 --> 00:10:26.610
Because it really isn't
just one disease.

00:10:26.610 --> 00:10:29.690
It's not like one type of
bacteria or one type of virus

00:10:29.690 --> 00:10:32.440
that you can pinpoint and
say let's attack this.

00:10:32.440 --> 00:10:36.800
Cancer is a whole class of
mutations where the cells

00:10:36.800 --> 00:10:40.250
start exhibiting this fast
invasive growth and this

00:10:40.250 --> 00:10:41.620
metastasis.

00:10:41.620 --> 00:10:44.520
So you might look at one type of
cancer and be able to say,

00:10:44.520 --> 00:10:48.700
hey, let's target the mutation
where the cells look like this

00:10:48.700 --> 00:10:52.020
and you're able to knock
out some of them.

00:10:52.020 --> 00:10:53.720
Let me do this in this color.

00:10:53.720 --> 00:10:55.300
So maybe you're able to
knock out that guy,

00:10:55.300 --> 00:10:56.160
that guy, that guy.

00:10:56.160 --> 00:11:00.030
But because their DNA
replication system might be

00:11:00.030 --> 00:11:02.160
broken in some way, they
continue to mutate, so

00:11:02.160 --> 00:11:04.790
eventually you have one version
that's able to not be

00:11:04.790 --> 00:11:06.590
knocked out by whatever
method you get.

00:11:06.590 --> 00:11:09.200
And so you have this kind of new
form of cancer, and then

00:11:09.200 --> 00:11:11.180
that new form of cancer is
even harder to kill.

00:11:11.180 --> 00:11:14.210
So you can imagine that
cancer is kind of a

00:11:14.210 --> 00:11:15.490
never ending fight.

00:11:15.490 --> 00:11:20.820
And you kind of have to attack
the general idea behind it.

00:11:20.820 --> 00:11:23.770
Chemotherapy and radiation, all
of these type of things.

00:11:23.770 --> 00:11:26.390
They try to attack things that
are fast growing because

00:11:26.390 --> 00:11:28.920
that's the kind of
one common theme

00:11:28.920 --> 00:11:30.030
behind all of the cancers.

00:11:30.030 --> 00:11:33.810
And we could do a whole playlist
on what cancer is and

00:11:33.810 --> 00:11:36.400
how people are attacking it, but
I wanted to at least show

00:11:36.400 --> 00:11:40.860
you in this video that cancer
really is just a byproduct of

00:11:40.860 --> 00:11:46.510
broken mitosis, or even more
specifically, broken DNA

00:11:46.510 --> 00:11:47.540
replication.

00:11:47.540 --> 00:11:53.100
That we have all of these cells
replicating themselves

00:11:53.100 --> 00:11:56.450
every day on the order of 100
billion, and every now and

00:11:56.450 --> 00:11:57.960
then something breaks.

00:11:57.960 --> 00:12:00.650
Usually when they break, either
nothing happens or the

00:12:00.650 --> 00:12:02.010
cell kills itself.

00:12:02.010 --> 00:12:05.960
But every now and then, the
cells start replicating even

00:12:05.960 --> 00:12:06.450
though they're broken.

00:12:06.450 --> 00:12:08.480
And sometimes they start
replicating like crazy.

00:12:08.480 --> 00:12:10.070
If they just replicate, but
they're really not doing any

00:12:10.070 --> 00:12:11.720
harm, it's benign.

00:12:11.720 --> 00:12:13.730
But if they start replicating
like crazy, taking over

00:12:13.730 --> 00:12:15.950
resources and spreading through
the body, you're

00:12:15.950 --> 00:12:17.410
dealing with a cancer.

00:12:17.410 --> 00:12:18.980
So hopefully, you found
that interesting.

00:12:18.980 --> 00:12:22.380
You already know a good bit of
the science that kind of deals

00:12:22.380 --> 00:12:27.680
with what is probably one of
the worst ailments that we

00:12:27.680 --> 00:12:30.470
deal with as creatures.

00:12:30.470 --> 00:12:32.150
I mean, obviously, we're not
the only people who can

00:12:32.150 --> 00:12:32.990
experience cancers.

00:12:32.990 --> 00:12:34.340
Even plants have cancers.


A look at a seductive but wrong Gibbs/spontaneity proof

WEBVTT
Kind: captions
Language: en

00:00:00.440 --> 00:00:03.110
In the video that I just did,
where I try to more rigorously

00:00:03.110 --> 00:00:06.910
prove the Gibbs free energy
relation, and that if this

00:00:06.910 --> 00:00:09.620
relation is less than zero
then this is spontaneous.

00:00:09.620 --> 00:00:12.890
I took great pains to make sure
that we use the proper

00:00:12.890 --> 00:00:15.100
definition of entropy.

00:00:15.100 --> 00:00:18.080
That every time that we said,
OK, a change in entropy from

00:00:18.080 --> 00:00:22.870
here to here is the heat
absorbed by a reversible

00:00:22.870 --> 00:00:25.050
process divided by the
temperature at

00:00:25.050 --> 00:00:26.290
which it was absorbed.

00:00:26.290 --> 00:00:28.630
And the change in entropy of
the environment is the

00:00:28.630 --> 00:00:30.990
opposite of that and, of course,
that is equal to zero.

00:00:30.990 --> 00:00:34.860
And I was very careful to
use this definition.

00:00:34.860 --> 00:00:36.920
And so you might have been
asking, hey Sal, there's a

00:00:36.920 --> 00:00:40.690
much simpler definition or
proof in my textbook.

00:00:40.690 --> 00:00:42.720
And I don't if it's in your
textbook, but it's in some of

00:00:42.720 --> 00:00:44.290
the ones that I've seen
and in some of the web

00:00:44.290 --> 00:00:45.470
pages I've looked at.

00:00:45.470 --> 00:00:48.960
Where they use a much simpler
argument that gets us

00:00:48.960 --> 00:00:51.240
eventually to this Gibbs
free energy relation.

00:00:51.240 --> 00:00:54.800
And I thought I would go over
it because as far as I can

00:00:54.800 --> 00:00:56.080
tell, it's incorrect.

00:00:56.080 --> 00:00:58.940
And what the argument tends to
go, is it says, look, the

00:00:58.940 --> 00:01:04.519
second law of thermodynamics
tells us, that for any

00:01:04.519 --> 00:01:13.870
spontaneous process, that delta
S is greater than zero.

00:01:13.870 --> 00:01:15.900
I agree with that completely
right now.

00:01:15.900 --> 00:01:17.900
And in order for delta S, and
that's delta S of the

00:01:17.900 --> 00:01:20.120
universe, is greater
than zero.

00:01:20.120 --> 00:01:25.760
And that means that delta S of
the system plus dealt S of the

00:01:25.760 --> 00:01:29.390
environment is going to
be greater than zero.

00:01:29.390 --> 00:01:32.090
and then this is the step that
you'll often see in a lot of

00:01:32.090 --> 00:01:35.020
textbooks and a lot of websites
that I disagree with.

00:01:35.020 --> 00:01:44.670
They'll say delta S of the
environment is equal to the

00:01:44.670 --> 00:01:53.100
heat or, let me say, the heat
absorbed by the environment,

00:01:53.100 --> 00:01:55.860
divided by the temperature
of the environment.

00:01:55.860 --> 00:01:57.540
And let's just say for
simplicity that everything

00:01:57.540 --> 00:01:59.685
here it's in some type of
temperature equilibrium.

00:01:59.685 --> 00:02:02.390
And it tends to be when we're
dealing with stuff in our

00:02:02.390 --> 00:02:06.150
chemistry sets in our
labs, whatever else.

00:02:06.150 --> 00:02:10.169
But the the reason why I
disagree with this step right

00:02:10.169 --> 00:02:13.810
here, that you see in a lot of
textbooks, is that this is not

00:02:13.810 --> 00:02:16.000
saying anything about the
reversibility of the reaction.

00:02:16.000 --> 00:02:19.810
You can only use this
thermodynamic definition of

00:02:19.810 --> 00:02:23.930
entropy if you know this heat
transfer is reversible.

00:02:26.850 --> 00:02:30.370
And when we're doing it in
general terms, we don't know

00:02:30.370 --> 00:02:31.070
whether it's reversal.

00:02:31.070 --> 00:02:33.690
In fact, if we're saying to
begin with that the reaction

00:02:33.690 --> 00:02:37.340
is spontaneous, that means
by definition that it's

00:02:37.340 --> 00:02:39.810
irreversible.

00:02:39.810 --> 00:02:43.370
So this is actually an
irreversible transfer of heat,

00:02:43.370 --> 00:02:45.990
which is not the definition
of entropy.

00:02:45.990 --> 00:02:47.990
The thermodynamic definition
of entropy is a

00:02:47.990 --> 00:02:49.200
very delicate one.

00:02:49.200 --> 00:02:52.030
You have to make sure that it
is a reversible reaction.

00:02:52.030 --> 00:02:54.470
Obviously, in a lot of first
year chemistry classes this

00:02:54.470 --> 00:02:55.160
doesn't matter.

00:02:55.160 --> 00:02:56.620
You're going to get the
question right.

00:02:56.620 --> 00:02:59.790
In fact, the question might be
dependent upon you making this

00:02:59.790 --> 00:03:00.760
incorrect assumption.

00:03:00.760 --> 00:03:02.550
So I don't want to confuse
you too much.

00:03:02.550 --> 00:03:04.620
But I want to show you that
this is not a right

00:03:04.620 --> 00:03:05.050
assumption.

00:03:05.050 --> 00:03:07.450
Because if you're assuming
something is spontaneous, and

00:03:07.450 --> 00:03:10.105
you're saying, OK, the change in
entropy in the environment

00:03:10.105 --> 00:03:13.400
is equal to the amount of heat
the environment absorbs,

00:03:13.400 --> 00:03:16.330
divided by T-- this is wrong
because this is not an

00:03:16.330 --> 00:03:18.030
irreversible reaction.

00:03:18.030 --> 00:03:21.690
But let's just see how this
argument tends to proceed.

00:03:21.690 --> 00:03:27.270
So they'll say, OK, this is
equal to delta S of our system

00:03:27.270 --> 00:03:32.440
plus the change in heat of our
environment, divided by the

00:03:32.440 --> 00:03:34.260
temperature of our
environment.

00:03:34.260 --> 00:03:36.980
They'll call this for the
environment, and that of

00:03:36.980 --> 00:03:39.940
course has to be
equal to zero.

00:03:39.940 --> 00:03:43.400
And they'll say, look, the
heat absorbed by the

00:03:43.400 --> 00:03:48.760
environment is equal to the
minus of the heat absorbed by

00:03:48.760 --> 00:03:49.680
the system.

00:03:49.680 --> 00:03:50.170
Right?

00:03:50.170 --> 00:03:52.230
It's either the system is
giving energy to the

00:03:52.230 --> 00:03:56.160
environment or the environment
is giving energy or heat to

00:03:56.160 --> 00:03:56.650
the system.

00:03:56.650 --> 00:03:58.770
So they are just going to be
the minus of each other.

00:03:58.770 --> 00:04:03.170
So the argument would go, well
this thing I can rewrite.

00:04:03.170 --> 00:04:08.130
This equation is the change in
entropy of the system, instead

00:04:08.130 --> 00:04:10.220
of writing a plus Q of the
environment here, I could

00:04:10.220 --> 00:04:15.480
write a minus Q of the system
over T is greater than zero.

00:04:15.480 --> 00:04:18.279
And then they multiply both
sides of this equation by T

00:04:18.279 --> 00:04:24.230
and you get T delta S of the
system minus the heat absorbed

00:04:24.230 --> 00:04:26.230
by the system is greater
than zero.

00:04:26.230 --> 00:04:28.760
You multiply both sides of this
by negative one and you

00:04:28.760 --> 00:04:32.880
get the heat absorbed by the
system minus the temperature

00:04:32.880 --> 00:04:35.990
times the change in entropy of
the system is greater than

00:04:35.990 --> 00:04:40.120
zero-- I'm sorry, is less than
zero when you multiply both

00:04:40.120 --> 00:04:42.090
sides by a negative, you
switch the signs.

00:04:42.090 --> 00:04:44.660
And then if you assume constant
pressure, this is the

00:04:44.660 --> 00:04:46.250
change in enthalpy
of the system.

00:04:46.250 --> 00:04:49.330
So you get the change in
enthalpy minus the temperature

00:04:49.330 --> 00:04:52.485
times delta S of the system
is less than zero.

00:04:52.485 --> 00:04:56.450
And they say, see this shows
that if you have a negative

00:04:56.450 --> 00:05:00.230
Gibbs free energy or change in
Gibbs free energy, then you're

00:05:00.230 --> 00:05:01.260
spontaneous.

00:05:01.260 --> 00:05:07.400
But all of that was predicated
on the idea that this could be

00:05:07.400 --> 00:05:09.780
rewritten like this.

00:05:09.780 --> 00:05:13.500
But it can't be rewritten like
that, because this is not a

00:05:13.500 --> 00:05:14.520
reversible process.

00:05:14.520 --> 00:05:16.170
We're starting from the
assumption that this is a

00:05:16.170 --> 00:05:18.560
spontaneous irreversible
process.

00:05:18.560 --> 00:05:22.410
And so you can't make this
substitution here.

00:05:22.410 --> 00:05:24.700
And that's why in the earlier
video I was very careful not

00:05:24.700 --> 00:05:26.090
to make that substitution.

00:05:26.090 --> 00:05:29.210
I was very careful to say, oh,
you know, the change in

00:05:29.210 --> 00:05:32.450
entropy of an irreversible
system that goes from here to

00:05:32.450 --> 00:05:39.800
here is the same as the change
in entropy as an irreversible

00:05:39.800 --> 00:05:41.920
system that goes from
there to there.

00:05:41.920 --> 00:05:43.090
Or let me say this
differently.

00:05:43.090 --> 00:05:45.550
The change in entropy of a
reversible system from there

00:05:45.550 --> 00:05:47.570
to there is the same as
an irreversible system

00:05:47.570 --> 00:05:48.300
from there to there.

00:05:48.300 --> 00:05:50.920
Although you don't know what
goes on in between for the

00:05:50.920 --> 00:05:52.240
irreversible.

00:05:52.240 --> 00:05:55.040
And so that's why I made
this comparison.

00:05:55.040 --> 00:05:59.340
This thing, and this thing are
the same, but then we compared

00:05:59.340 --> 00:06:01.830
the heat absorbed by an
irreversible system, and we

00:06:01.830 --> 00:06:04.910
showed that it's less than the
heat absorbed by a reversible

00:06:04.910 --> 00:06:08.090
system because it's generating
its own friction.

00:06:08.090 --> 00:06:10.760
And from that, we got this
relation, which we were able

00:06:10.760 --> 00:06:13.250
to then go and get the Gibbs
free energy relation.

00:06:13.250 --> 00:06:16.730
So, anyway, I don't want to make
a video that's too geeky

00:06:16.730 --> 00:06:21.470
or too particular, or
kind of trying to

00:06:21.470 --> 00:06:23.330
really pick at the details.

00:06:23.330 --> 00:06:26.210
But I think it's an important
point to make because so much

00:06:26.210 --> 00:06:29.000
of what we talk about,
especially in thermodynamics,

00:06:29.000 --> 00:06:30.485
is our definition of entropy.

00:06:30.485 --> 00:06:33.090
And it's very important we use
the correct one, and we don't

00:06:33.090 --> 00:06:36.700
take what I would argue are
incorrect shortcuts, because

00:06:36.700 --> 00:06:40.320
this is not the definition
of entropy right there.


More rigorous Gibbs free energy / spontaneity relationship

WEBVTT
Kind: captions
Language: en

00:00:00.500 --> 00:00:03.510
I've hopefully given you a bit
of a gut feeling behind where

00:00:03.510 --> 00:00:06.180
the formula of Gibbs Free
Energy comes from.

00:00:06.180 --> 00:00:08.039
In this video I want to do
something a little bit more

00:00:08.039 --> 00:00:10.320
rigorous and actually,
I guess you could

00:00:10.320 --> 00:00:12.270
say derive the formula.

00:00:12.270 --> 00:00:15.620
So to do that, let's just study
two systems that have

00:00:15.620 --> 00:00:17.660
the exact same change
in entropy.

00:00:17.660 --> 00:00:22.195
To depict that, I'll get out
our handy PV diagram.

00:00:24.790 --> 00:00:26.160
What we're going to do is we're
going to compare two

00:00:26.160 --> 00:00:31.020
systems. One that's this
perfect, reversible system and

00:00:31.020 --> 00:00:33.860
one that's irreversible or
a spontaneous system.

00:00:33.860 --> 00:00:36.020
So they're both going
to start here.

00:00:36.020 --> 00:00:39.990
They're going to go from this
point on the PV diagram to

00:00:39.990 --> 00:00:42.260
this point right here.

00:00:42.260 --> 00:00:44.980
And before we go into exactly
what they're doing, I think

00:00:44.980 --> 00:00:47.490
it's a good review to kind
of talk about what an

00:00:47.490 --> 00:00:49.730
irreversible process and
what a reversible

00:00:49.730 --> 00:00:51.120
process really is.

00:00:51.120 --> 00:00:53.920
An irreversible process is this
theoretical thing where

00:00:53.920 --> 00:00:57.950
you have no friction, where
you're always so close to

00:00:57.950 --> 00:01:00.950
equilibrium that you can
always go backwards.

00:01:00.950 --> 00:01:04.004
You're always-- you can kind of
view that the reaction is

00:01:04.004 --> 00:01:06.010
never really proceeding
forward or backwards.

00:01:06.010 --> 00:01:08.960
Although obviously it is moving,
so it's a very-- it

00:01:08.960 --> 00:01:11.820
actually doesn't really exist
in nature, but it's a useful

00:01:11.820 --> 00:01:13.000
theoretical construct.

00:01:13.000 --> 00:01:14.880
So let me draw a little.

00:01:14.880 --> 00:01:19.870
So if this is a-- I'll get
the good old pistons out.

00:01:19.870 --> 00:01:22.530
So let's say this is an--
I'll do it twice.

00:01:22.530 --> 00:01:25.870
So that's my irreversible
piston-- That'll be my

00:01:25.870 --> 00:01:28.810
reversible, this is going
to be my irreversible.

00:01:28.810 --> 00:01:31.480
Let me draw them.

00:01:31.480 --> 00:01:33.820
OK, and let me label them.

00:01:33.820 --> 00:01:36.270
So this right here is going
to be reversible.

00:01:36.270 --> 00:01:40.240
And this right here is going
to be irreversible.

00:01:40.240 --> 00:01:42.305
Or it could also be considered
spontaneous.

00:01:46.260 --> 00:01:47.710
Using the key word.

00:01:47.710 --> 00:01:49.580
That's going to matter for
Gibbs Free Energy.

00:01:49.580 --> 00:01:52.740
But all spontaneous reactions
are irreversible.

00:01:52.740 --> 00:01:54.870
So they're going to go from
this state to this state.

00:01:54.870 --> 00:01:58.220
So in our reversible
world, we have this

00:01:58.220 --> 00:02:00.900
little cap to our piston.

00:02:00.900 --> 00:02:06.350
And we have our gas in here,
exerting some pressure.

00:02:06.350 --> 00:02:08.470
And what we'd have is
a bunch of pebbles.

00:02:08.470 --> 00:02:10.759
We have a bunch of
pebbles out here.

00:02:10.759 --> 00:02:14.080
And we slowly remove the
pebbles one by one.

00:02:14.080 --> 00:02:18.010
And as we remove the pebbles,
our piston-- or this movable

00:02:18.010 --> 00:02:20.990
ceiling up here-- will
move upwards.

00:02:20.990 --> 00:02:22.390
It'll move upwards.

00:02:22.390 --> 00:02:26.020
So the pressure will push up,
but as we move up, we will

00:02:26.020 --> 00:02:29.590
have lower and lower pressure
because the gases will bounce

00:02:29.590 --> 00:02:31.110
into the surface less.

00:02:31.110 --> 00:02:32.500
And we'll have a higher,
higher volume.

00:02:32.500 --> 00:02:36.150
So as we move each
infinitesimally small grain of

00:02:36.150 --> 00:02:38.730
sand, and we're going to do it
super slow, that we're always

00:02:38.730 --> 00:02:40.600
infinitely close
to equilibrium.

00:02:40.600 --> 00:02:43.270
We're going to move from this
state to this state.

00:02:43.270 --> 00:02:46.470
And even better, let's view that
this is the first stage

00:02:46.470 --> 00:02:47.530
of our Carnot cycle.

00:02:47.530 --> 00:02:52.270
Let's say in either case, we're
on top of a reservoir.

00:02:52.270 --> 00:02:55.470
So in either case, both of these
systems are on top of

00:02:55.470 --> 00:02:58.980
this infinite reservoir that
has a temperature T1.

00:02:58.980 --> 00:03:01.650
And what that does it keeps
the temperature constant.

00:03:01.650 --> 00:03:04.140
So we're going to travel
along an isotherm.

00:03:04.140 --> 00:03:07.870
Because normally if we were to
remove these things and if we

00:03:07.870 --> 00:03:10.130
just allowed it to occur
adiabatically, we would

00:03:10.130 --> 00:03:11.620
actually lose temperature.

00:03:11.620 --> 00:03:13.360
We would actually lose
average kinetic

00:03:13.360 --> 00:03:14.910
energy as work is done.

00:03:14.910 --> 00:03:16.940
But in this case we have
this reservoir.

00:03:16.940 --> 00:03:21.220
So heat is just going to be
transferred to my system.

00:03:21.220 --> 00:03:22.510
Heat is going to
be transferred.

00:03:22.510 --> 00:03:25.230
So let me call that QR.

00:03:25.230 --> 00:03:25.490
Right?

00:03:25.490 --> 00:03:30.250
If the reservoir wasn't here,
our temperature would go down.

00:03:30.250 --> 00:03:33.940
But since we do have the
reservoir, we will constantly

00:03:33.940 --> 00:03:35.220
be transferring heat.

00:03:35.220 --> 00:03:35.900
And we've seen this.

00:03:35.900 --> 00:03:38.410
This is just the first phase
of the Carnot cycle.

00:03:38.410 --> 00:03:40.500
We'll move along an isotherm
like this.

00:03:40.500 --> 00:03:42.430
This is the reversible case.

00:03:42.430 --> 00:03:45.300
And the only reason why we can
even draw the state at every

00:03:45.300 --> 00:03:48.590
point here is because reversible
processes are

00:03:48.590 --> 00:03:49.480
quasistatic.

00:03:49.480 --> 00:03:52.740
They're always infinitely
close to equilibrium.

00:03:52.740 --> 00:03:54.510
And when we say reversible,
we're also saying there's no

00:03:54.510 --> 00:03:57.840
friction between this little
piston in the cylinder.

00:03:57.840 --> 00:04:00.363
That if we put a grain of sand
back, it'll go exactly to

00:04:00.363 --> 00:04:01.260
where it was before.

00:04:01.260 --> 00:04:02.890
And no energy was lost
because there was no

00:04:02.890 --> 00:04:04.450
heat of friction there.

00:04:04.450 --> 00:04:06.650
So this is what the graph
of the reversible

00:04:06.650 --> 00:04:08.460
process would look like.

00:04:08.460 --> 00:04:10.670
Now what does the graph of the
error irreversible-- Well,

00:04:10.670 --> 00:04:11.110
actually no.

00:04:11.110 --> 00:04:13.410
I won't draw the graph, but
let's talk about what the

00:04:13.410 --> 00:04:16.050
irreversible process is
going to be like.

00:04:16.050 --> 00:04:18.600
So it's going to look similar.

00:04:18.600 --> 00:04:19.680
It's going to look like that.

00:04:19.680 --> 00:04:22.760
It's going to have
its gases there.

00:04:22.760 --> 00:04:24.830
But for the sake of an argument,
to get from that

00:04:24.830 --> 00:04:26.810
state to that state, instead of
moving the pebbles one by

00:04:26.810 --> 00:04:30.220
one, let's say I have
these big blocks.

00:04:30.220 --> 00:04:33.240
And when I remove one of these
big blocks, I go from that

00:04:33.240 --> 00:04:34.440
state to that state.

00:04:34.440 --> 00:04:36.470
But obviously all hell
breaks loose.

00:04:36.470 --> 00:04:39.280
So I'm not really defined in
this in between state.

00:04:39.280 --> 00:04:42.420
But I definitely go from that
state to that state once I go

00:04:42.420 --> 00:04:43.920
back to equilibrium.

00:04:43.920 --> 00:04:47.420
Now the other key thing in the
irreversible process-- and

00:04:47.420 --> 00:04:49.880
every real process in our world
is irreversible-- is

00:04:49.880 --> 00:04:53.210
that you're going to
have friction here.

00:04:53.210 --> 00:04:56.320
As this moves up, it's going to
rub against the side of the

00:04:56.320 --> 00:05:00.690
container and generate
heat of friction.

00:05:00.690 --> 00:05:02.980
So let me call that
heat of friction.

00:05:02.980 --> 00:05:05.100
So let me ask you a question.

00:05:05.100 --> 00:05:09.220
If, in this case, Q sub R had
to be added to the system to

00:05:09.220 --> 00:05:15.960
maintain its temperature, what's
going to be the Q sub

00:05:15.960 --> 00:05:17.200
irreversible here?

00:05:17.200 --> 00:05:21.200
How much has to be added to this
system in order to keep

00:05:21.200 --> 00:05:23.280
it at the constant
temperature T1?

00:05:23.280 --> 00:05:25.840
Will it have to be more or less
than what was added to

00:05:25.840 --> 00:05:27.870
the reversible system?

00:05:27.870 --> 00:05:32.480
Well this guy, as this piston
moves up, he's generating some

00:05:32.480 --> 00:05:33.530
of his own heat.

00:05:33.530 --> 00:05:37.410
So if this was an adiabatic
process, he wouldn't lose as

00:05:37.410 --> 00:05:39.210
much temperature as
this guy would.

00:05:39.210 --> 00:05:43.210
So he's going to need less heat
from the reservoir in

00:05:43.210 --> 00:05:45.400
order to maintain
his temperature.

00:05:45.400 --> 00:05:45.760
At T1.

00:05:45.760 --> 00:05:48.220
In order to get to this
point on the isotherm.

00:05:48.220 --> 00:05:50.310
Remember, this irreversible
process, we don't know what

00:05:50.310 --> 00:05:51.010
happens over here.

00:05:51.010 --> 00:05:52.960
He might be travelling
on some crazy path.

00:05:52.960 --> 00:05:55.570
In fact, we can't even define
the path, because it goes out

00:05:55.570 --> 00:05:56.580
of equilibrium.

00:05:56.580 --> 00:05:57.670
So it's going to be
some crazy thing.

00:05:57.670 --> 00:06:00.830
But we know it pops back on the
PV diagram right there.

00:06:00.830 --> 00:06:03.810
But because it's generating some
of its own heat from the

00:06:03.810 --> 00:06:07.255
friction, it's going to need
less heat from the reservoir.

00:06:07.255 --> 00:06:09.270
So let me write that down.

00:06:09.270 --> 00:06:12.050
The heat absorbed by the
reversible process is going to

00:06:12.050 --> 00:06:16.050
be greater than the heat
absorbed by the

00:06:16.050 --> 00:06:18.180
irreversible process.

00:06:18.180 --> 00:06:20.790
And that's because the
irreversible process is

00:06:20.790 --> 00:06:22.760
generating friction.

00:06:22.760 --> 00:06:23.960
Fair enough.

00:06:23.960 --> 00:06:26.690
Now what is the change in
entropy for both systems?

00:06:26.690 --> 00:06:28.500
Well they both started here.

00:06:28.500 --> 00:06:29.720
And they both ended here.

00:06:29.720 --> 00:06:31.520
And entropy is a
state variable.

00:06:31.520 --> 00:06:37.220
So the change in entropy for
the reversible process is

00:06:37.220 --> 00:06:47.150
going to be equal to the change
in entropy for the

00:06:47.150 --> 00:06:48.650
irreversible process.

00:06:48.650 --> 00:06:52.290
They're both going from
there to there.

00:06:52.290 --> 00:06:55.460
And obviously the entropy
has changed.

00:06:55.460 --> 00:06:57.850
We're going from one state
to another state.

00:06:57.850 --> 00:07:00.620
And the entropy, well I won't
go too much into it.

00:07:00.620 --> 00:07:01.720
But let's ask another
question.

00:07:01.720 --> 00:07:05.190
What is the total change in
entropy of the universe for

00:07:05.190 --> 00:07:07.380
the reversible process?

00:07:07.380 --> 00:07:10.640
So for the universe, that's
going to be-- Our universe

00:07:10.640 --> 00:07:12.960
here is the reservoir
in our system.

00:07:12.960 --> 00:07:14.040
So let me write here.

00:07:14.040 --> 00:07:16.240
Reversible.

00:07:16.240 --> 00:07:17.260
I don't want to run
out of space.

00:07:17.260 --> 00:07:18.670
Let me see, I'll do it
in a different color.

00:07:18.670 --> 00:07:20.700
So this is the reversible
process.

00:07:20.700 --> 00:07:23.510
So the change in entropy of the
universe is equal to the

00:07:23.510 --> 00:07:29.050
change in entropy of our
reversible process plus the

00:07:29.050 --> 00:07:33.390
change in entropy of-- oh, I
already used R for reversible,

00:07:33.390 --> 00:07:36.670
so let's call it the reserv--
well, the first three letters

00:07:36.670 --> 00:07:41.350
are the same, so let me call
it of our environment.

00:07:41.350 --> 00:07:41.900
Right?

00:07:41.900 --> 00:07:46.195
And then the reversible process,
the change in entropy

00:07:46.195 --> 00:07:49.436
of our reversible process is
the heat added for our

00:07:49.436 --> 00:07:50.370
reversible process.

00:07:50.370 --> 00:07:52.730
And we can use this definition
because it is

00:07:52.730 --> 00:07:54.890
a reversible process.

00:07:54.890 --> 00:07:57.690
It's that over T1.

00:07:57.690 --> 00:08:00.500
And then what's the change in
entropy of our environment?

00:08:00.500 --> 00:08:02.830
Well it's giving away Q sub R.

00:08:02.830 --> 00:08:03.230
Right?

00:08:03.230 --> 00:08:06.850
So its heat absorbed
is minus Q sub R.

00:08:06.850 --> 00:08:08.700
And, of course, it's at a
constant temperature.

00:08:08.700 --> 00:08:11.180
It is a heat reservoir.

00:08:11.180 --> 00:08:12.540
It's at T1.

00:08:12.540 --> 00:08:15.090
So it equals 0.

00:08:15.090 --> 00:08:16.510
It equals 0.

00:08:16.510 --> 00:08:17.440
Interesting.

00:08:17.440 --> 00:08:19.990
So actually I should take
a little side note here.

00:08:19.990 --> 00:08:24.500
That, the change in entropy of
the universe for a reversible

00:08:24.500 --> 00:08:26.440
process is 0.

00:08:26.440 --> 00:08:28.590
And actually that should make
a lot of intuitive sense

00:08:28.590 --> 00:08:31.040
because the whole point of a
reversal process is you could

00:08:31.040 --> 00:08:34.370
go in this direction, or you
could go in that direction.

00:08:34.370 --> 00:08:36.360
It's always so close people to
equilibrium you can move in

00:08:36.360 --> 00:08:37.360
either direction.

00:08:37.360 --> 00:08:39.890
And if the entropy was greater
than 0 in one direction, it

00:08:39.890 --> 00:08:42.289
would have to be less than
0 on the other direction.

00:08:42.289 --> 00:08:44.540
So it wouldn't be able to go in
the other direction by the

00:08:44.540 --> 00:08:45.550
second law of thermodynamics.

00:08:45.550 --> 00:08:49.110
So it actually makes sense
that the entropy of the

00:08:49.110 --> 00:08:51.390
universe-- the change in entropy
of the universe, not

00:08:51.390 --> 00:08:53.270
just of the system--
when a reversible

00:08:53.270 --> 00:08:56.000
process occurs, is 0.

00:08:56.000 --> 00:08:57.860
Let's see if we can relate
that to the irreversible

00:08:57.860 --> 00:09:00.490
process So if I wanted to
figure out the change in

00:09:00.490 --> 00:09:04.750
entropy of the irreversible
process-- What's the change in

00:09:04.750 --> 00:09:08.870
entropy of the irreversible
process?

00:09:08.870 --> 00:09:15.130
And then let me subtract from
that the heat that was taken

00:09:15.130 --> 00:09:19.200
away from the reservoir, from
the irreversible process, Q

00:09:19.200 --> 00:09:24.300
sub IR, and of course
all this over T1.

00:09:24.300 --> 00:09:27.870
What is this going to be equal
to in relation to 0?

00:09:27.870 --> 00:09:28.350
Remember this is an

00:09:28.350 --> 00:09:31.980
irreversible, spontaneous process.

00:09:31.980 --> 00:09:35.770
Well, this value, the
irreversible process is

00:09:35.770 --> 00:09:37.220
starting here and going there.

00:09:37.220 --> 00:09:41.010
So its change in delta S is the
exact same thing as that.

00:09:41.010 --> 00:09:44.460
Change in delta S is the same
as the reversible process.

00:09:44.460 --> 00:09:47.130
So these two things
are equivalent.

00:09:47.130 --> 00:09:49.810
Now, I just told you that since
there's some heat of

00:09:49.810 --> 00:09:53.810
friction, this guy has to take
in less heat from the

00:09:53.810 --> 00:09:55.550
reservoir than this guy.

00:09:55.550 --> 00:09:57.380
So if this-- and I
wrote it here.

00:09:57.380 --> 00:09:58.940
I mean, let me clean this
thing up a little bit.

00:09:58.940 --> 00:10:00.670
I wrote it right here.

00:10:00.670 --> 00:10:03.530
Q sub IR, the heat that the
irreversible process has to

00:10:03.530 --> 00:10:05.570
take from the reservoir, because
generating its own

00:10:05.570 --> 00:10:08.160
heat from friction, is less
than the heat from the

00:10:08.160 --> 00:10:09.610
reversal process.

00:10:09.610 --> 00:10:14.150
So this number, right here, is
less than this number here.

00:10:14.150 --> 00:10:16.360
Or you could view it this way.

00:10:16.360 --> 00:10:18.560
This number here was
equal to this.

00:10:18.560 --> 00:10:21.560
So this number here is going
to be less than this.

00:10:21.560 --> 00:10:31.870
So this has to be greater than
0 for the irreversible,

00:10:31.870 --> 00:10:38.150
spontaneous process.

00:10:38.150 --> 00:10:42.130
Now let's just do a little
bit of mathematics.

00:10:42.130 --> 00:10:45.340
So this is the heat that was
essentially given to the

00:10:45.340 --> 00:10:46.910
irreversible system.

00:10:46.910 --> 00:10:48.600
It's a minus here because
this is the term.

00:10:48.600 --> 00:10:51.220
It's kind of taken away from
the actual reservoir.

00:10:51.220 --> 00:10:54.650
So let's just do a little bit
of-- let's just multiply all

00:10:54.650 --> 00:10:56.825
sides of this equation by T1.

00:10:56.825 --> 00:11:04.980
And we get T1 times delta S of
the irreversible process minus

00:11:04.980 --> 00:11:10.000
Q of the irreversible process
is greater than 0.

00:11:10.000 --> 00:11:13.550
Now, well, let's just--
So what is this?

00:11:13.550 --> 00:11:16.220
How can we say this?

00:11:16.220 --> 00:11:18.680
But let's actually just multiply
both sides of this by

00:11:18.680 --> 00:11:19.420
negative 1.

00:11:19.420 --> 00:11:20.590
And remember, this
is true for any

00:11:20.590 --> 00:11:22.090
irreversible, spontaneous process.

00:11:22.090 --> 00:11:23.450
If you multiply both
sides of this by

00:11:23.450 --> 00:11:25.680
negative 1, you get this.

00:11:25.680 --> 00:11:30.970
The heat added to the
irreversible process minus T

00:11:30.970 --> 00:11:34.990
times delta S of the
irreversible process is going

00:11:34.990 --> 00:11:37.200
to be less than 0.

00:11:37.200 --> 00:11:38.840
This is true for any

00:11:38.840 --> 00:11:42.230
irreversible, spontaneous process.

00:11:42.230 --> 00:11:44.080
And at this point,
this should look

00:11:44.080 --> 00:11:46.320
reasonably familiar to you.

00:11:46.320 --> 00:11:49.240
When we wrote the Gibbs Free
Energy formula, we said change

00:11:49.240 --> 00:11:55.950
in G is equal to delta H
minus T times delta S.

00:11:55.950 --> 00:11:59.310
And we said that if this is less
than 0, then we have a

00:11:59.310 --> 00:12:00.560
spontaneous process.

00:12:03.500 --> 00:12:04.510
And this all makes sense.

00:12:04.510 --> 00:12:06.590
Because these two are equivalent
to each other.

00:12:06.590 --> 00:12:07.750
What's the only difference
here?

00:12:07.750 --> 00:12:09.710
Here we wrote heat added
to the system.

00:12:09.710 --> 00:12:11.260
Here we wrote change
in enthalpy.

00:12:11.260 --> 00:12:14.400
And I've done three or four
videos right now, where I say

00:12:14.400 --> 00:12:18.860
that change in enthalpy is equal
to the heat added to a

00:12:18.860 --> 00:12:23.560
system, as long as we're
dealing with a constant

00:12:23.560 --> 00:12:26.270
pressure system.

00:12:26.270 --> 00:12:29.750
So we get this result just by
comparing a irreversible to a

00:12:29.750 --> 00:12:30.560
reversible system.

00:12:30.560 --> 00:12:31.750
And this is true for all

00:12:31.750 --> 00:12:34.790
irreversible, spontaneous processes.

00:12:34.790 --> 00:12:37.100
And then if we assume that we're
dealing with a constant

00:12:37.100 --> 00:12:39.130
pressure system-- so you can
forget a little bit of what I

00:12:39.130 --> 00:12:42.072
just drew, because we know
that this is true, and we

00:12:42.072 --> 00:12:44.420
assume constant pressure--
then we get to this.

00:12:44.420 --> 00:12:46.720
And then we know that if
something is spontaneous, then

00:12:46.720 --> 00:12:50.590
this right here must
be less than 0.

00:12:50.590 --> 00:12:53.590
So hopefully you found that
a little bit interesting.

00:12:53.590 --> 00:12:56.320
Actually I'll do one
more point here.

00:12:56.320 --> 00:13:01.390
This kind of gels with the
idea that second law of

00:13:01.390 --> 00:13:04.810
thermodynamics tells us that for
any spontaneous process,

00:13:04.810 --> 00:13:10.400
delta S is going to be greater
than or equal-- or well for

00:13:10.400 --> 00:13:13.330
any spontaneous process, is
going to be greater than 0.

00:13:13.330 --> 00:13:16.090
Because although this right
here isn't the formal

00:13:16.090 --> 00:13:20.390
definition of entropy, because
we're not dealing with a

00:13:20.390 --> 00:13:22.510
reversible process here,
you can kind of

00:13:22.510 --> 00:13:23.500
think of it that way.

00:13:23.500 --> 00:13:26.100
And so, at least, on an
intuitive level it gets you

00:13:26.100 --> 00:13:29.350
there, that we have delta
S greater than 0.

00:13:29.350 --> 00:13:32.270
And I won't fixate on that too
much, because what I did

00:13:32.270 --> 00:13:34.890
earlier in the video is more
rigorous than what I'm heading

00:13:34.890 --> 00:13:35.560
to right now.

00:13:35.560 --> 00:13:40.820
So hopefully that gives you a
sense of where you can get to

00:13:40.820 --> 00:13:44.140
the Gibbs Free Energy formula,
and how it drives spontaneous

00:13:44.140 --> 00:13:46.900
reactions from just our basic
understanding of what

00:13:46.900 --> 00:13:49.790
reversible and irreversible
processes are, and how they

00:13:49.790 --> 00:13:53.830
relate to entropy and heat
exchange and enthalpy.


Gibbs free energy example

WEBVTT
Kind: captions
Language: en

00:00:00.410 --> 00:00:02.730
I have this reaction here
where if I had a mole of

00:00:02.730 --> 00:00:05.970
methane, and I react that with
two moles of oxygen, I'll

00:00:05.970 --> 00:00:08.045
produce a mole of carbon
dioxide and

00:00:08.045 --> 00:00:09.680
two moles of water.

00:00:09.680 --> 00:00:12.380
And what we want to answer in
this video is whether this

00:00:12.380 --> 00:00:14.760
reaction is spontaneous.

00:00:14.760 --> 00:00:17.290
And we learned in the last
video that to answer that

00:00:17.290 --> 00:00:19.810
question, we have to turn to
Gibbs free energy, or the

00:00:19.810 --> 00:00:21.620
change in Gibbs free energy.

00:00:21.620 --> 00:00:25.320
And the change in Gibbs free
energy is equal to the

00:00:25.320 --> 00:00:29.300
enthalpy change for the reaction
minus the temperature

00:00:29.300 --> 00:00:32.820
at which it is occurring, times
the change in entropy.

00:00:32.820 --> 00:00:35.840
And if this is less than
zero, then it's

00:00:35.840 --> 00:00:39.240
a spontaneous reaction.

00:00:39.240 --> 00:00:41.860
So I gave us a little
bit of a head start.

00:00:41.860 --> 00:00:46.070
I just calculated the change in
enthalpy for this reaction,

00:00:46.070 --> 00:00:47.530
and that's right here.

00:00:47.530 --> 00:00:48.460
And we know how to do that.

00:00:48.460 --> 00:00:50.230
We've done that several
videos ago.

00:00:50.230 --> 00:00:52.900
You could just look up the heats
of formation of each of

00:00:52.900 --> 00:00:54.880
these products.

00:00:54.880 --> 00:00:56.950
For water you'll multiply
it by 2, since you

00:00:56.950 --> 00:00:58.180
have 2 moles of it.

00:00:58.180 --> 00:01:00.510
And so you have the heats of
formation of all the products,

00:01:00.510 --> 00:01:02.500
and then you subtract
out the heats of

00:01:02.500 --> 00:01:03.780
formation of all the reactants.

00:01:03.780 --> 00:01:07.270
And of course the heat of
formation of O2 is O, so this

00:01:07.270 --> 00:01:11.040
won't even show up in it, and
you'll get minus 890.3

00:01:11.040 --> 00:01:11.590
kilojoules.

00:01:11.590 --> 00:01:15.090
Well, this tells us that this
is an exothermic reaction.

00:01:15.090 --> 00:01:18.490
That this side of the equation
has less energy in it-- you

00:01:18.490 --> 00:01:20.450
could kind of think of it
that way-- is that side.

00:01:20.450 --> 00:01:22.450
So some energy must have
been released.

00:01:22.450 --> 00:01:25.400
We could even put here, you
know, plus e for energy.

00:01:25.400 --> 00:01:27.980
Let me write, plus some energy
is going to be released.

00:01:27.980 --> 00:01:29.750
So that's why it's exothermic.

00:01:29.750 --> 00:01:32.010
But our question is, is
this spontaneous?

00:01:32.010 --> 00:01:34.100
So to figure out if it's
spontaneous, we also have to

00:01:34.100 --> 00:01:36.140
figure out our delta s.

00:01:39.450 --> 00:01:42.690
And to help figure out the
delta s I, ahead of time,

00:01:42.690 --> 00:01:46.090
looked up the standard
molar entropies for

00:01:46.090 --> 00:01:48.130
each of these molecules.

00:01:48.130 --> 00:01:50.460
So for example, the standard--
I'll write it here in a

00:01:50.460 --> 00:01:51.710
different color.

00:02:00.510 --> 00:02:04.980
The standard-- you put a little
naught symbol there--

00:02:04.980 --> 00:02:08.389
the standard molar entropy-- so
when we say standard, it's

00:02:08.389 --> 00:02:11.039
at 298 degrees Kelvin.

00:02:11.039 --> 00:02:12.730
Actually, I shouldn't
say degrees Kelvin.

00:02:12.730 --> 00:02:15.680
It's at 298 Kelvin You don't
use the word degrees,

00:02:15.680 --> 00:02:17.440
necessarily, when you
talk about Kelvin.

00:02:17.440 --> 00:02:21.020
So it's at 298 Kelvin, which is
25 degrees Celsius, so it's

00:02:21.020 --> 00:02:21.880
at room temperature.

00:02:21.880 --> 00:02:24.690
So that's why it's considered
standard temperature.

00:02:24.690 --> 00:02:29.700
So the standard entropy of
methane at room temperature is

00:02:29.700 --> 00:02:30.980
equal to this number
right here.

00:02:30.980 --> 00:02:37.880
186 joules per Kelvin mole.

00:02:37.880 --> 00:02:42.320
So if I have 1 mole of methane,
I have 186 joules per

00:02:42.320 --> 00:02:43.930
Kelvin of entropy.

00:02:43.930 --> 00:02:46.050
If I have 2 moles, I
multiply that by 2.

00:02:46.050 --> 00:02:48.780
If I have 3 moles, I
multiply that by 3.

00:02:48.780 --> 00:02:54.870
So the total change in entropy
of this reaction is the total

00:02:54.870 --> 00:02:58.950
standard entropies of the
products minus the total

00:02:58.950 --> 00:03:00.610
standard entropies
of the reactants.

00:03:00.610 --> 00:03:02.450
Just like what we did
with enthalpy.

00:03:02.450 --> 00:03:11.650
So that's going to be equal to
213.6 plus-- I have 2 moles of

00:03:11.650 --> 00:03:12.190
water here.

00:03:12.190 --> 00:03:17.810
So it's plus 2 times-- let's
just write 70 there.

00:03:17.810 --> 00:03:20.090
69.9, almost 70.

00:03:20.090 --> 00:03:24.720
Plus 2 times 70, and then I
want to subtract out the

00:03:24.720 --> 00:03:28.920
entropy of the reactants, or
this side of the reaction.

00:03:28.920 --> 00:03:42.900
So the entropy of 1 mole of CH4
is 186 plus 2 times 205.

00:03:42.900 --> 00:03:45.430
So just eyeballing it already,
this number is close to this

00:03:45.430 --> 00:03:48.220
number, but this number is much
larger than this number.

00:03:48.220 --> 00:03:50.620
Liquid water has a much
lower-- this is

00:03:50.620 --> 00:03:51.650
liquid water's entropy.

00:03:51.650 --> 00:03:54.970
It has a much lower entropy
than oxygen gas.

00:03:54.970 --> 00:03:55.730
And that makes sense.

00:03:55.730 --> 00:04:00.150
Because liquid formed, there's
a lot fewer states.

00:04:00.150 --> 00:04:02.630
It all falls to the bottom of
the container, as opposed to

00:04:02.630 --> 00:04:04.680
kind of taking the shape of
the room and expanding.

00:04:04.680 --> 00:04:06.600
So a gas is naturally going
to have much higher

00:04:06.600 --> 00:04:08.230
entropy than a liquid.

00:04:08.230 --> 00:04:11.830
So just eyeballing it, we can
already see that our products

00:04:11.830 --> 00:04:13.930
are going to have a lower
entropy than our reactants.

00:04:13.930 --> 00:04:15.400
So this is probably going
to be a negative number.

00:04:15.400 --> 00:04:19.430
But let's confirm that.

00:04:19.430 --> 00:04:30.610
So I have 200, 213.6 plus--
well, plus 140, right?

00:04:30.610 --> 00:04:31.270
2 times 70.

00:04:31.270 --> 00:04:35.540
Plus 140 is equal to 353.6.

00:04:35.540 --> 00:04:39.930
So this is 353.6.

00:04:39.930 --> 00:04:47.580
And then from that, I'm going to
subtract out-- so 186 plus

00:04:47.580 --> 00:04:54.790
2 times 205 is equal to 596.

00:04:54.790 --> 00:04:58.900
So minus 596, and what
is that equal to?

00:04:58.900 --> 00:05:06.780
So we put the minus 596, and
then plus the 353.6, and we

00:05:06.780 --> 00:05:10.910
have minus 242.4.

00:05:10.910 --> 00:05:18.220
So this is equal to minus 242.4
joules per Kelvin is our

00:05:18.220 --> 00:05:21.820
delta s minus.

00:05:21.820 --> 00:05:23.800
So we lose that much entropy.

00:05:23.800 --> 00:05:26.020
And those units might not make
sense to you right now, and

00:05:26.020 --> 00:05:28.780
actually you know these are
but of arbitrary units.

00:05:28.780 --> 00:05:30.750
But you can just say, hey, this
is getting more ordered.

00:05:30.750 --> 00:05:33.710
And it makes sense, because
we have a ton of gas.

00:05:33.710 --> 00:05:36.080
We have 3 separate molecules,
1 here and 2

00:05:36.080 --> 00:05:38.230
molecules of oxygen.

00:05:38.230 --> 00:05:40.840
And then we go to 3 molecules
again, but the

00:05:40.840 --> 00:05:42.310
water is now liquid.

00:05:42.310 --> 00:05:45.770
So it makes sense to me
that we lose entropy.

00:05:45.770 --> 00:05:47.330
There's fewer states
that the liquid,

00:05:47.330 --> 00:05:48.790
especially, can take on.

00:05:48.790 --> 00:05:51.650
But let's figure out whether
this reaction is spontaneous.

00:05:51.650 --> 00:05:57.440
So our delta g is equal
to our delta h.

00:05:57.440 --> 00:06:01.140
We're releasing energy,
so it's minus 890.

00:06:01.140 --> 00:06:02.510
I'll just get rid
of the decimals.

00:06:02.510 --> 00:06:04.490
We don't have to be
that precise.

00:06:04.490 --> 00:06:06.350
Minus our temperature.

00:06:06.350 --> 00:06:09.220
We're assuming that we're at
room temperature, or 298

00:06:09.220 --> 00:06:10.340
degrees Kelvin.

00:06:10.340 --> 00:06:13.400
That's 28-- I should just
say, 298 Kelvin.

00:06:13.400 --> 00:06:14.590
I should get in the habit
of not saying

00:06:14.590 --> 00:06:15.960
degrees when I say Kelvin.

00:06:15.960 --> 00:06:22.750
Which is 25 degrees Celsius,
times our change in entropy.

00:06:22.750 --> 00:06:25.050
Now, this is going
to be a minus.

00:06:25.050 --> 00:06:27.760
Now you might say, OK, minus
242, you might want to put

00:06:27.760 --> 00:06:28.530
that there.

00:06:28.530 --> 00:06:30.280
But you have to be very,
very, very careful.

00:06:30.280 --> 00:06:33.160
This right here is
in kilojoules.

00:06:33.160 --> 00:06:35.190
This right here is in joules.

00:06:35.190 --> 00:06:37.540
So if we want to write
everything in kilojoules,

00:06:37.540 --> 00:06:39.660
since we already wrote that
down, let's write this in

00:06:39.660 --> 00:06:40.370
kilojoules.

00:06:40.370 --> 00:06:46.620
So it's 0.242 kilojoules
per Kelvin.

00:06:52.370 --> 00:06:55.790
And so now our Gibbs free energy
right here is going to

00:06:55.790 --> 00:07:00.880
be minus 890 kilojoules minus
290-- so the minus and the

00:07:00.880 --> 00:07:02.760
minus, you get a plus.

00:07:02.760 --> 00:07:05.770
And that makes sense, that the
entropy term is going to make

00:07:05.770 --> 00:07:08.480
our Gibbs free energy
more positive.

00:07:08.480 --> 00:07:11.480
Which, as we know, since we want
to get this thing below

00:07:11.480 --> 00:07:13.980
0, this is going to fight
the spontaneity.

00:07:13.980 --> 00:07:18.840
But let's see if it can
overwhelm the actual enthalpy,

00:07:18.840 --> 00:07:20.470
the exothermic nature of it.

00:07:20.470 --> 00:07:22.480
And it seems like it will,
because you multiply a

00:07:22.480 --> 00:07:24.010
fraction times this,
it's going to be a

00:07:24.010 --> 00:07:25.090
smaller number than that.

00:07:25.090 --> 00:07:27.560
But let's just figure it out.

00:07:27.560 --> 00:07:31.830
So divided by 1, 2, 3.

00:07:31.830 --> 00:07:37.170
That's our change in entropy
times 298, that's our

00:07:37.170 --> 00:07:40.410
temperature, is minus 72.

00:07:40.410 --> 00:07:43.710
So this term becomes-- and then
we put a minus there-- so

00:07:43.710 --> 00:07:47.360
it's plus 72.2.

00:07:47.360 --> 00:07:50.300
So this is the entropy term
at standard temperature.

00:07:50.300 --> 00:07:51.370
It turns into that.

00:07:51.370 --> 00:07:52.970
And this is our enthalpy term.

00:07:52.970 --> 00:07:55.900
So we can already see that the
enthalpy is a much more

00:07:55.900 --> 00:07:58.320
negative number than our
positive term from our

00:07:58.320 --> 00:08:00.480
temperature times our
change in entropy.

00:08:00.480 --> 00:08:04.530
So this term is going
to win out.

00:08:04.530 --> 00:08:08.330
Even though we lose entropy in
this reaction, it releases so

00:08:08.330 --> 00:08:10.840
much energy that's going
to be spontaneous.

00:08:10.840 --> 00:08:14.340
This is definitely less than
0, so this is going to be a

00:08:14.340 --> 00:08:17.360
spontaneous reaction.

00:08:17.360 --> 00:08:19.520
As you can see, these Gibbs free
energy problems, they're

00:08:19.520 --> 00:08:20.630
really not too difficult.

00:08:20.630 --> 00:08:23.900
You just really need to
find these values.

00:08:23.900 --> 00:08:27.230
And to find these values, it'll
either be given, the

00:08:27.230 --> 00:08:29.670
delta h, but we know how to
solve for the delta h.

00:08:29.670 --> 00:08:31.720
You just look up the heats
of formations of all the

00:08:31.720 --> 00:08:35.210
products, subtract out the
reactants, and of course you

00:08:35.210 --> 00:08:38.110
wait by the coefficients.

00:08:38.110 --> 00:08:40.490
And then, to figure out the
change in entropy, you do the

00:08:40.490 --> 00:08:40.909
same thing.

00:08:40.909 --> 00:08:44.020
You have to look up the standard
molar entropies of

00:08:44.020 --> 00:08:46.840
the products' weight by the
coefficients, subtract out the

00:08:46.840 --> 00:08:50.110
reactants, and then just
substitute in here, and then

00:08:50.110 --> 00:08:51.850
you essentially have the
Gibbs free energy.

00:08:51.850 --> 00:08:54.640
And in this case,
it was negative.

00:08:54.640 --> 00:08:56.570
Now, you could imagine a
situation where we're at a

00:08:56.570 --> 00:08:57.720
much higher temperature.

00:08:57.720 --> 00:09:00.890
Like the surface of the sun or
something, where all of a

00:09:00.890 --> 00:09:06.380
sudden, instead of a 298 here,
if you had like a 2,000 or a

00:09:06.380 --> 00:09:08.140
4,000 there.

00:09:08.140 --> 00:09:10.700
Then all of a sudden, things
become interesting.

00:09:10.700 --> 00:09:14.710
If you could imagine, if
you had a 40,000 Kelvin

00:09:14.710 --> 00:09:17.530
temperature here, then all of a
sudden the entropy term, the

00:09:17.530 --> 00:09:20.150
loss of entropy, is going
to matter a lot more.

00:09:20.150 --> 00:09:22.480
And so this term, this positive
term, is going to

00:09:22.480 --> 00:09:25.870
outweigh this, and maybe it
wouldn't be spontaneous at a

00:09:25.870 --> 00:09:27.960
very, very, very, very
high temperature.

00:09:27.960 --> 00:09:29.160
Another way to think about it.

00:09:29.160 --> 00:09:34.560
A reaction that generates heat
that lets out heat-- the heat

00:09:34.560 --> 00:09:37.090
being released doesn't matter so
much when there's already a

00:09:37.090 --> 00:09:39.980
lot of heat or kinetic energy
in the environment.

00:09:39.980 --> 00:09:42.920
If the temperature was high
enough, this reaction would

00:09:42.920 --> 00:09:46.050
not be spontaneous, because
maybe then the entropy term

00:09:46.050 --> 00:09:46.980
would win out.

00:09:46.980 --> 00:09:49.130
But anyway, I just wanted to do
this calculation for you to

00:09:49.130 --> 00:09:51.360
show you that there's nothing
too abstract here.

00:09:51.360 --> 00:09:53.950
You can look up everything on
the web, and then figure out

00:09:53.950 --> 00:09:56.320
if something is going
to be spontaneous.