Vapor pressure

WEBVTT
Kind: captions
Language: en

00:00:00.640 --> 00:00:04.150
We know that when we have some
substance in a liquid state,

00:00:04.150 --> 00:00:08.790
it has enough kinetic energy for
the molecules to move past

00:00:08.790 --> 00:00:11.530
each other, but still not
enough energy for the

00:00:11.530 --> 00:00:15.100
molecules to completely move
away from each other.

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So, for example, this
is a liquid.

00:00:16.530 --> 00:00:18.960
Maybe they're moving
in that direction.

00:00:18.960 --> 00:00:21.590
These guys are moving a little
bit slower in that direction

00:00:21.590 --> 00:00:24.490
so there's a bit of this flow
going on, but still there are

00:00:24.490 --> 00:00:25.540
bonds between them.

00:00:25.540 --> 00:00:28.060
They kind of switch between
different molecules, but they

00:00:28.060 --> 00:00:29.380
want to stay close
to each other.

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There are these little bonds
between them and they want to

00:00:32.330 --> 00:00:32.940
stay close.

00:00:32.940 --> 00:00:37.260
If you increase the average
kinetic energy enough, or

00:00:37.260 --> 00:00:39.470
essentially increase the
temperature enough and then

00:00:39.470 --> 00:00:43.810
overcome the heat of fusion, we
know that, all of a sudden,

00:00:43.810 --> 00:00:46.740
even these bonds aren't strong
enough to even keep them

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close, and the molecules
separate and they get into a

00:00:50.850 --> 00:00:52.560
gaseous phase.

00:00:52.560 --> 00:00:55.050
And there they have a lot of
kinetic energy, and they're

00:00:55.050 --> 00:00:59.320
bouncing around, and they take
the shape of their container.

00:00:59.320 --> 00:01:02.090
But there's an interesting
thing to think about.

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Temperature is average
kinetic energy.

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Which implies, and it's true,
that all of the molecules do

00:01:15.160 --> 00:01:18.940
not have the same
kinetic energy.

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Let's say even they did.

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Then these guys would bump into
this guy, and you could

00:01:23.310 --> 00:01:25.430
think of them as billiard balls,
and they transfer all

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of the momentum to this guy.

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Now this guy has a ton
of kinetic energy.

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These guys have a lot less.

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This guy has a ton.

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These guys have a lot less.

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There's a huge distribution
of kinetic energy.

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If you look at the surface
atoms or the surface

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molecules, and I care about the
surface molecules because

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those are the first ones
to vaporize or-- I

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shouldn't jump the gun.

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They're the ones capable of
leaving if they had enough

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kinetic energy.

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If I were to draw a distribution
of the surface

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molecules-- let me draw
a little graph here.

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So in this dimension, I have
kinetic energy, and on this

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dimension, this is just a
relative concentration.

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And this is just my best
estimate, but it should give

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you the idea.

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So there's some average
kinetic energy at some

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temperature, right?

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This is the average
kinetic energy.

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And then the kinetic energy of
all the parts, it's going to

00:02:23.650 --> 00:02:27.090
be a distribution around that,
so maybe it looks something

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like this: a bell curve.

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You could watch the statistics
videos to learn more about the

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normal distribution, but
I think the normal

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distribution-- this is supposed
to be a normal, so it

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just gets smaller and smaller
as you go there.

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And so at any given time,
although the average is here,

00:02:43.820 --> 00:02:44.970
there's some molecules
that have a

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very low kinetic energy.

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They're moving slowly or maybe
they have-- well, let's just

00:02:49.590 --> 00:02:50.960
say they're moving slowly.

00:02:50.960 --> 00:02:53.510
And at any given time, you have
some molecules that have

00:02:53.510 --> 00:02:55.770
a very high kinetic energy,
maybe just because of the

00:02:55.770 --> 00:02:59.950
random bumps that it gets
from other molecules.

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It's accrued a lot of velocity
or at least a lot of momentum.

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So the question arises,
are any of these

00:03:06.740 --> 00:03:08.680
molecules fast enough?

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Do they have enough kinetic
energy to escape?

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And so there is some
kinetic energy.

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I'll draw some threshold here,
where if you have more than

00:03:16.520 --> 00:03:18.710
that amount of kinetic energy,
you actually have enough to

00:03:18.710 --> 00:03:20.970
escape if you are
surface atom.

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Now, there could be a dude down
here who has a ton of

00:03:24.520 --> 00:03:26.050
kinetic energy.

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But in order for him to escape,
he'd have to bump

00:03:28.760 --> 00:03:31.760
through all these other liquid
molecules on the way out, so

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it's a very-- in fact, he
probably won't escape.

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It's the surface atoms that we
care about because those are

00:03:36.540 --> 00:03:38.360
the ones that are interfacing
directly with

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the pressure outside.

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So let's say this is
the gas outside.

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It's going to be much
less dense.

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It doesn't have to be, but
let's assume it is.

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These are the guys that kind
of can escape into the air

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above it, if we assume that
there's some air above it.

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So at any given time, there's
some fraction of the particles

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or the molecules that
can escape.

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So you're next question is, hey,
well, doesn't that mean

00:04:04.670 --> 00:04:07.470
that they will be vaporized or
they will turn into gas?

00:04:07.470 --> 00:04:09.600
And yes, it does.

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So at any given time,
you have some

00:04:11.480 --> 00:04:14.440
molecules that are escaping.

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Those molecules-- what it's
called is evaporation.

00:04:17.970 --> 00:04:19.350
This isn't a foreign
concept to you.

00:04:19.350 --> 00:04:22.510
If you leave water outside, it
will evaporate, even though

00:04:22.510 --> 00:04:25.600
outside, hopefully, in your
place, is below the boiling

00:04:25.600 --> 00:04:27.950
temperature, or the normal
boiling temperature of water.

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The normal boiling point is
just the boiling point at

00:04:30.090 --> 00:04:31.560
atmospheric pressure.

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If you just leave water out,
over time, it will evaporate.

00:04:36.070 --> 00:04:39.460
What happens is some of these
molecules that have unusually

00:04:39.460 --> 00:04:42.820
high kinetic energy do escape.

00:04:42.820 --> 00:04:45.990
They do escape, and if you have
your pot or pan outside

00:04:45.990 --> 00:04:48.606
or, even better, outside of your
house, what happens is

00:04:48.606 --> 00:04:51.840
they escape, and then
the wind blows.

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The wind will blow and then
blow these guys away.

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And then a few more will escape,
the wind blows and

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blows them all away.

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And a few more escape, and
the wind blows and blows

00:04:59.330 --> 00:05:00.440
them all the way.

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So over time, you'll end up with
an empty pan that once

00:05:03.810 --> 00:05:05.050
held water.

00:05:05.050 --> 00:05:07.020
Now, the question is
what happens if you

00:05:07.020 --> 00:05:09.210
have a closed system?

00:05:09.210 --> 00:05:13.200
Well, we've all done that
experiment, either on purpose

00:05:13.200 --> 00:05:14.980
or inadvertently, leaving
something outside and seeing

00:05:14.980 --> 00:05:19.010
that the water will evaporate.

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What happens in a closed system
where there isn't wind

00:05:21.450 --> 00:05:22.100
to blow away?

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So let me just draw--
there you go.

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Let's say a closed system, and I
have-- it doesn't have to be

00:05:31.920 --> 00:05:34.060
water, but I have some
liquid down here.

00:05:38.720 --> 00:05:42.350
And there's some pressure
from the air above it.

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Let's just say it was at
atmospheric pressure.

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It doesn't have to be.

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So there's some air and
the air has some

00:05:47.710 --> 00:05:50.990
kinetic energy over here.

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So, of course, do the
water molecules.

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And some of them start
to evaporate.

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So some of the water molecules
that are up here in the

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distribution, they have enough
energy to escape, so they

00:06:02.010 --> 00:06:06.890
start hanging out with the
air molecules, right?

00:06:06.890 --> 00:06:08.050
Now something interesting
happens.

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This is the distribution
of the molecules

00:06:10.285 --> 00:06:11.570
in the liquid state.

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Well, there's also a
distribution of the kinetic

00:06:14.350 --> 00:06:16.080
energies of the molecules
in the gaseous state.

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Just like different things are
bumping into each other and

00:06:18.650 --> 00:06:21.410
gaining and losing kinetic
energy down here, the same

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thing is happening up here.

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So maybe this guy has a lot of
kinetic energy, but he bumps

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into stuff and he loses it.

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And then he'll come back down.

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So there's some set
of molecules.

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I'll do it in another
set of blue.

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These are still the water-- or
whatever the fluid we're

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talking about-- that come back
from the vapor state back into

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the liquid state.

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And so what happens is, there's
always a bit of

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evaporation and there's always
a bit of condensation because

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you always have this

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distribution of kinetic energies.

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At any given moment in time,
out of the vapor above the

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liquid, some of the vapor loses
its kinetic energy and

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then it goes back into
the liquid state.

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Some of the surface liquid gains
kinetic energy by random

00:07:03.060 --> 00:07:07.050
bumps and whatever else and
goes into the vapor state.

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And the vapor state will
continue to happen until you

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get to some type
of equilibrium.

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And when you get that
equilibrium, we're at some

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pressure up here.

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So let me see, some pressure.

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And the pressure is caused by
these vapor particles over

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here, and that pressure is
called the vapor pressure.

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I want to make sure you
understand this.

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So the vapor pressure is the
pressure created, and this is

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at a given temperature for
a given molecule, right?

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Every molecule or every type
of substance will have a

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different vapor pressure at
different temperatures, and

00:07:51.810 --> 00:07:53.720
obviously every different type
of substance will also have

00:07:53.720 --> 00:07:55.130
different vapor pressures.

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For a given temperature and
a given molecule, it's the

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pressure at which you have a
pressure created by the vapor

00:08:00.860 --> 00:08:03.010
molecules where you have
an equilibrium.

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Where you have just as many
things vaporizing as things

00:08:06.310 --> 00:08:08.120
going back into the
liquid state.

00:08:08.120 --> 00:08:10.310
And we learned before that the
more pressure you have, the

00:08:10.310 --> 00:08:13.780
harder it is to vaporize
even more, right?

00:08:13.780 --> 00:08:17.530
We learned in the phase state
things that if you are at 100

00:08:17.530 --> 00:08:20.190
degrees at ultra-high pressure,
and you were dealing

00:08:20.190 --> 00:08:22.410
with water, you would still
be in the liquid state.

00:08:22.410 --> 00:08:26.290
So the vapor creates some
pressure and it'll keep

00:08:26.290 --> 00:08:28.240
happening, depending
on how badly this

00:08:28.240 --> 00:08:30.320
liquid wants to evaporate.

00:08:30.320 --> 00:08:34.630
But it keeps vaporizing until
the point that you have just

00:08:34.630 --> 00:08:37.309
as much-- I guess you could kind
of view it as density up

00:08:37.309 --> 00:08:38.780
here, but I don't want to
think-- you have just as many

00:08:38.780 --> 00:08:41.919
molecules here converting into
this state as molecules here

00:08:41.919 --> 00:08:43.789
converting into this state.

00:08:43.789 --> 00:08:46.420
So just to get an intuition of
what vapor pressure is or how

00:08:46.420 --> 00:08:48.750
it goes with different
molecules, molecules that

00:08:48.750 --> 00:08:59.930
really want to evaporate-- and
so why would a molecule want

00:08:59.930 --> 00:09:00.350
to evaporate?

00:09:00.350 --> 00:09:04.350
It could have high kinetic
energy, so this would be at a

00:09:04.350 --> 00:09:06.530
high temperature.

00:09:06.530 --> 00:09:11.690
It could have low intermolecular
forces, right?

00:09:11.690 --> 00:09:14.620
It could be molecular.

00:09:14.620 --> 00:09:17.250
Obviously, the noble gases
have very low molecular

00:09:17.250 --> 00:09:22.200
forces, but in general, most
hydrocarbons or gasoline or

00:09:22.200 --> 00:09:24.480
methane or all of these things,
they really want to

00:09:24.480 --> 00:09:26.570
evaporate because they have
much lower intermolecular

00:09:26.570 --> 00:09:28.330
forces than, say, water.

00:09:28.330 --> 00:09:30.110
Or they could just be
light molecules.

00:09:32.910 --> 00:09:35.550
You could look at the physics
lectures, but kinetic energy

00:09:35.550 --> 00:09:38.320
it's a function of mass
and velocity.

00:09:38.320 --> 00:09:41.830
So you could have a pretty
respectable kinetic energy

00:09:41.830 --> 00:09:44.880
because you have a high mass
and a low velocity.

00:09:44.880 --> 00:09:48.480
So if you have a light mass and
the same kinetic energy,

00:09:48.480 --> 00:09:49.905
you're more likely to have
a higher velocity.

00:09:49.905 --> 00:09:52.150
You could watch the kinetic
energy videos for that.

00:09:52.150 --> 00:09:57.010
But something that wants to
evaporate, a lot of its

00:09:57.010 --> 00:10:00.240
molecules-- let me do it
in a different color.

00:10:00.240 --> 00:10:03.860
Something that wants to
evaporate really bad, a lot

00:10:03.860 --> 00:10:07.130
more of its molecules will have
to enter into this vapor

00:10:07.130 --> 00:10:12.890
state in order for the
equilibrium to be reached.

00:10:12.890 --> 00:10:15.370
Let me do it all in
the same color.

00:10:15.370 --> 00:10:20.810
So the pressure created by its
evaporated molecules is going

00:10:20.810 --> 00:10:23.900
to be higher for it to get to
that equilibrium state, so it

00:10:23.900 --> 00:10:25.395
has high vapor pressure.

00:10:34.020 --> 00:10:36.540
And on the other side, if you're
at a low temperature or

00:10:36.540 --> 00:10:40.160
you have strong intermolecular
forces or you have a heavy

00:10:40.160 --> 00:10:44.450
molecule, then you're going to
have a low vapor pressure.

00:10:44.450 --> 00:10:50.490
For example, iron has a very
low vapor pressure because

00:10:50.490 --> 00:10:54.220
it's not vaporizing while--
let me think of something.

00:10:54.220 --> 00:10:56.450
Carbon dioxide has
a relatively much

00:10:56.450 --> 00:10:57.620
higher vapor pressure.

00:10:57.620 --> 00:11:00.460
Much more of carbon dioxide
is going to evaporate

00:11:00.460 --> 00:11:01.300
when you have it.

00:11:01.300 --> 00:11:02.770
Well, I really shouldn't use
that because you're going

00:11:02.770 --> 00:11:05.140
straight from the liquid to the
solid state, but I think

00:11:05.140 --> 00:11:06.110
you get the idea.

00:11:06.110 --> 00:11:09.060
And something that has a high
vapor pressure, that wants to

00:11:09.060 --> 00:11:15.120
evaporate really bad, we say
it has a high volatility.

00:11:15.120 --> 00:11:16.620
You've probably heard
that word before.

00:11:23.850 --> 00:11:28.390
So, for example, gasoline has a
higher-- it's more volatile

00:11:28.390 --> 00:11:31.060
than water, and that's why it
evaporates, and it also has a

00:11:31.060 --> 00:11:32.230
higher vapor pressure.

00:11:32.230 --> 00:11:34.780
Because if you were to put it
in a closed container, more

00:11:34.780 --> 00:11:39.170
gasoline at the same temperature
and the same

00:11:39.170 --> 00:11:42.120
atmospheric pressure, will enter
into the vapor state.

00:11:42.120 --> 00:11:46.990
And so that vapor state will
generate more pressure to

00:11:46.990 --> 00:11:53.330
offset the natural inclination
of the gasoline to want to

00:11:53.330 --> 00:11:55.750
escape than in the
case with water.

00:11:55.750 --> 00:11:59.340
Now, an interesting thing
happens when this vapor

00:11:59.340 --> 00:12:02.700
pressure is equal to the
atmospheric pressure.

00:12:02.700 --> 00:12:05.990
So right now, this is our closed
container and you have

00:12:05.990 --> 00:12:08.370
the atmosphere here at
a certain pressure.

00:12:08.370 --> 00:12:11.790
Let's say until now, we've
assumed that the atmosphere

00:12:11.790 --> 00:12:14.540
was at a higher pressure, for
the most part keeping these

00:12:14.540 --> 00:12:16.010
molecules contained.

00:12:16.010 --> 00:12:18.440
Maybe some atmosphere molecules
are coming in here,

00:12:18.440 --> 00:12:21.740
and maybe some of the vapor
molecules are escaping a bit,

00:12:21.740 --> 00:12:23.820
but it's keeping it contained
because this is at a higher

00:12:23.820 --> 00:12:27.020
pressure out here than
this vapor pressure.

00:12:27.020 --> 00:12:30.490
And of course the pressure right
here, at the surface of

00:12:30.490 --> 00:12:32.700
the molecule, is going to be the
combination of the partial

00:12:32.700 --> 00:12:35.900
pressure due to the few
atmospheric molecules that

00:12:35.900 --> 00:12:38.060
come in, plus the
vapor pressure.

00:12:38.060 --> 00:12:41.480
But once that vapor pressure
becomes equal to that

00:12:41.480 --> 00:12:45.060
atmospheric pressure, so it can
press out with the same

00:12:45.060 --> 00:12:48.020
amount of force-- you can kind
of view it as force per area--

00:12:48.020 --> 00:12:51.260
so then the molecules
can start to escape.

00:12:51.260 --> 00:12:53.490
It can push the atmosphere
back.

00:12:53.490 --> 00:12:55.600
And so you start having
a gap here.

00:12:55.600 --> 00:12:59.530
You start having a vacuum.

00:12:59.530 --> 00:13:01.410
I don't want to use exactly
a vacuum, but since the

00:13:01.410 --> 00:13:04.610
molecules escaped, more and more
of these molecules can

00:13:04.610 --> 00:13:05.280
start going out.

00:13:05.280 --> 00:13:07.560
And at that point, you've
reached the boiling point of

00:13:07.560 --> 00:13:10.580
the substance when the vapor
pressure is equal to the

00:13:10.580 --> 00:13:12.250
atmospheric pressure.

00:13:12.250 --> 00:13:15.760
Just to get a sense of what all
of this means, let's look

00:13:15.760 --> 00:13:18.300
at the vapor pressure
for water.

00:13:18.300 --> 00:13:22.540
This is water right here, H2O.

00:13:22.540 --> 00:13:25.640
I should do that in black.

00:13:25.640 --> 00:13:31.190
And so you see at 760-- so
atmospheric pressure, we're in

00:13:31.190 --> 00:13:35.185
torr now, but that's just a
different-- 760 torr is equal

00:13:35.185 --> 00:13:38.310
to 1 atmosphere, so that's
about right.

00:13:38.310 --> 00:13:41.610
That's about right there,
so it's 1 atmosphere.

00:13:41.610 --> 00:13:46.140
So at atmospheric pressure,
the vapor pressure at 100

00:13:46.140 --> 00:13:50.520
degrees Celsius for water-- the
vapor is at 100 degrees

00:13:50.520 --> 00:13:51.370
Celsius for water.

00:13:51.370 --> 00:13:54.330
Or I guess another way to put
it, at 100 degrees Celsius,

00:13:54.330 --> 00:14:00.260
you have 760 torr of vapor
pressure, which is exactly the

00:14:00.260 --> 00:14:03.820
atmospheric pressure, or 1
atmosphere, at sea level.

00:14:03.820 --> 00:14:08.070
So at 100 degrees, vapor
pressure is equal to

00:14:08.070 --> 00:14:10.185
atmospheric, or sea
level atmospheric.

00:14:12.770 --> 00:14:15.500
And so you're going to boil,
which we all know is true.

00:14:15.500 --> 00:14:19.970
And then at lower temperatures,
your vapor

00:14:19.970 --> 00:14:22.850
pressure is going to
be lower than the

00:14:22.850 --> 00:14:24.370
atmospheric pressure, right?

00:14:24.370 --> 00:14:26.780
Let's see, here it looks
like 300 something.

00:14:26.780 --> 00:14:27.650
But then what happens?

00:14:27.650 --> 00:14:30.590
If you lowered the atmospheric
pressure enough, if you were

00:14:30.590 --> 00:14:34.370
to pump air out of the
container, or whatever, low

00:14:34.370 --> 00:14:37.950
enough, so if you brought the
atmospheric pressure down to

00:14:37.950 --> 00:14:40.620
this vapor pressure, then again,
you will have boiling.

00:14:40.620 --> 00:14:43.390
And we saw that in the phase
change diagrams, that you can

00:14:43.390 --> 00:14:46.480
boil something at a lower
temperature if you lower the

00:14:46.480 --> 00:14:47.710
atmospheric pressure.

00:14:47.710 --> 00:14:49.660
And that's because you're
lowering the atmospheric

00:14:49.660 --> 00:14:54.070
pressure to the vapor pressure
of the substance.

00:14:54.070 --> 00:14:56.360
And here's a comparative
chart, and this is

00:14:56.360 --> 00:14:56.790
interesting.

00:14:56.790 --> 00:14:59.670
You see this is kind of an
exponential increase with

00:14:59.670 --> 00:15:03.270
temperature of vapor pressure.

00:15:03.270 --> 00:15:05.760
And that's because, if you think
about that distribution

00:15:05.760 --> 00:15:08.850
we did before, this is at
one kinetic energy.

00:15:08.850 --> 00:15:11.660
If you increase the amount of
kinetic energy, then your

00:15:11.660 --> 00:15:13.100
distribution will
look like this.

00:15:13.100 --> 00:15:14.620
The temperature has gone up.

00:15:14.620 --> 00:15:16.770
And now you have a
lot, lot more.

00:15:16.770 --> 00:15:17.650
It's not just linear.

00:15:17.650 --> 00:15:20.890
You have a lot more particles
that can now escape and have

00:15:20.890 --> 00:15:24.620
the kinetic energy
to evaporate.

00:15:24.620 --> 00:15:26.720
And you can see it's this
exponential increase as you

00:15:26.720 --> 00:15:28.030
increase the temperature.

00:15:28.030 --> 00:15:29.060
Now, here's another chart.

00:15:29.060 --> 00:15:30.990
You say, hey, where's that
exponential increase going?

00:15:30.990 --> 00:15:32.990
That's because this is
a logarithmic chart.

00:15:32.990 --> 00:15:35.880
You can see the scale.

00:15:35.880 --> 00:15:41.110
It increases exponentially as
opposed to linearly, so it

00:15:41.110 --> 00:15:44.530
goes from 0.1 to 10, so equal
distances are actually up by a

00:15:44.530 --> 00:15:46.010
factor of 10, so that's
why you don't see

00:15:46.010 --> 00:15:47.600
that logarithmic move.

00:15:47.600 --> 00:15:49.860
But these are just for
different substances.

00:15:49.860 --> 00:15:53.390
Propane, you see at any given--
so let's go at like a

00:15:53.390 --> 00:15:54.160
decent temperature.

00:15:54.160 --> 00:15:56.472
Let's go 20 degrees Celsius.

00:15:56.472 --> 00:16:02.940
At 20 Celsius, propane has the
highest vapor pressure.

00:16:02.940 --> 00:16:08.310
So this is 1 atmosphere, so
propane will actually

00:16:08.310 --> 00:16:11.615
evaporate, will actually boil
at 20 degrees Celsius.

00:16:11.615 --> 00:16:13.440
It will actually completely
boil and go

00:16:13.440 --> 00:16:14.520
into the gaseous state.

00:16:14.520 --> 00:16:17.410
Because its vapor pressure
is so much higher than

00:16:17.410 --> 00:16:20.470
atmospheric pressure, if we're
assuming we're at sea level.

00:16:20.470 --> 00:16:22.910
And you could do that for
different molecules.

00:16:22.910 --> 00:16:24.730
Methyl chloride is
the next one.

00:16:24.730 --> 00:16:26.430
It's a slightly lower
vapor pressure,

00:16:26.430 --> 00:16:28.250
but still very volatile.

00:16:28.250 --> 00:16:31.660
It would still definitely boil
and turn into the gaseous

00:16:31.660 --> 00:16:34.390
state at 20 degrees Celsius if
we're at sea level because sea

00:16:34.390 --> 00:16:36.330
level is right there.

00:16:36.330 --> 00:16:39.150
Let's see, at sea level, if you
wanted to keep something--

00:16:39.150 --> 00:16:41.750
so sea level is this pressure--
if you wanted to

00:16:41.750 --> 00:16:46.010
keep let's say, methyl
chloride.

00:16:46.010 --> 00:16:49.980
If you wanted to keep methyl
chloride in the liquid state,

00:16:49.980 --> 00:16:52.170
or in equilibrium with the
liquid state instead of

00:16:52.170 --> 00:16:53.580
boiling, you would have
to be at least at

00:16:53.580 --> 00:16:54.240
around-- what is this?

00:16:54.240 --> 00:16:58.010
Minus 25 degrees Celsius
in order for that.

00:16:58.010 --> 00:17:00.430
Propane, even at minus 25
degrees is still in the

00:17:00.430 --> 00:17:03.290
gaseous state because its vapor

00:17:03.290 --> 00:17:05.480
pressure is still higher.

00:17:05.480 --> 00:17:10.140
And then, of course, if you
have butane, for example.

00:17:10.140 --> 00:17:17.720
Butane I think is what they put
in lighters, but butane

00:17:17.720 --> 00:17:21.550
will be in the liquid state as
long as you're at around

00:17:21.550 --> 00:17:22.720
roughly 0 degrees.

00:17:22.720 --> 00:17:24.560
In a lighter, you might say,
oh, it's in a liquid state.

00:17:24.560 --> 00:17:27.140
They probably increase the
pressure so the pressure in

00:17:27.140 --> 00:17:28.680
the lighter is probably
something higher.

00:17:28.680 --> 00:17:33.930
Maybe it's at 2 atmospheres or
something, so that the butane

00:17:33.930 --> 00:17:35.940
at room temperature will stay
in the liquid state.

00:17:35.940 --> 00:17:36.220
Who knows?

00:17:36.220 --> 00:17:38.160
I don't know what the pressure
is in there.

00:17:38.160 --> 00:17:39.930
This is just an interesting
chart to look at, that there's

00:17:39.930 --> 00:17:41.690
actually a bunch of different
vapor pressures.

00:17:41.690 --> 00:17:44.870
You can see at atmospheric
pressure what's likely to be a

00:17:44.870 --> 00:17:47.060
gas or a liquid at different
temperatures, and then you

00:17:47.060 --> 00:17:50.310
could see at different
temperatures, which are the

00:17:50.310 --> 00:17:52.440
things that are most volatile
and how much do you have to

00:17:52.440 --> 00:17:56.000
increase or decrease the
pressure to evaporate

00:17:56.000 --> 00:17:57.280
something or to boil it.

00:17:57.280 --> 00:17:58.820
Anyway, hopefully you
found that useful.

00:17:58.820 --> 00:18:01.260
Vapor pressure is something that
we encounter every day,

00:18:01.260 --> 00:18:03.660
and I'll see you in
the next video.


Phase diagrams

WEBVTT
Kind: captions
Language: en

00:00:00.830 --> 00:00:03.670
All of the phase changes we've
been doing so far have been

00:00:03.670 --> 00:00:05.980
under constant pressure
conditions, and, in

00:00:05.980 --> 00:00:07.940
particular, with the problems
that I've been doing with

00:00:07.940 --> 00:00:11.480
water phase changes in the last
couple of videos, it was

00:00:11.480 --> 00:00:14.330
at atmospheric pressure, at
least at sea level atmospheric

00:00:14.330 --> 00:00:15.860
pressure, or at 1 atmosphere.

00:00:15.860 --> 00:00:17.290
So it was done-- well,
I'll explain this

00:00:17.290 --> 00:00:18.450
diagram in a second.

00:00:18.450 --> 00:00:21.140
But we all know that in the
universe, pressure isn't

00:00:21.140 --> 00:00:23.190
always constant and it
definitely isn't always

00:00:23.190 --> 00:00:24.460
constant at 1 atmosphere.

00:00:24.460 --> 00:00:27.060
1 atmosphere was defined
as the pressure at

00:00:27.060 --> 00:00:28.080
sea level on Earth.

00:00:28.080 --> 00:00:31.320
Obviously, pressure will vary
wildly if you go to smaller

00:00:31.320 --> 00:00:35.460
planets or larger planets, or
have thicker atmospheres, or

00:00:35.460 --> 00:00:38.640
if we're just doing different
types of applications dealing

00:00:38.640 --> 00:00:40.660
with gases and liquids
and solids.

00:00:40.660 --> 00:00:45.460
So what I've drawn here
is a phase diagram.

00:00:45.460 --> 00:00:46.710
Let me write that down.

00:00:50.480 --> 00:00:53.930
And there are many forms of
phase diagrams. This is the

00:00:53.930 --> 00:00:56.480
most common form that you might
see in your chemistry

00:00:56.480 --> 00:01:00.200
class or on some standardized
test, but what it captures is

00:01:00.200 --> 00:01:03.240
the different states of matter
and when they transition

00:01:03.240 --> 00:01:05.590
according to temperature
and pressure.

00:01:05.590 --> 00:01:08.010
This is the phase diagram
for water.

00:01:08.010 --> 00:01:11.870
So just to understand what's
going on here, is that on this

00:01:11.870 --> 00:01:13.485
axis, I have pressure.

00:01:16.520 --> 00:01:19.630
On the x-axis, I have
temperature, and at any given

00:01:19.630 --> 00:01:21.650
point, this diagram will tell
you whether you're dealing

00:01:21.650 --> 00:01:27.690
with a solid, so solid will
be here, a liquid will

00:01:27.690 --> 00:01:34.160
be here, or a gas.

00:01:34.160 --> 00:01:42.160
For example, if I told you that
I was at 0 degrees, let's

00:01:42.160 --> 00:01:47.340
say 0 degrees is right there,
if I'm at 0 degrees Celsius

00:01:47.340 --> 00:01:49.820
and 1 atmosphere, where am I?

00:01:49.820 --> 00:01:52.400
So 0 degrees, 1 atmosphere,
I'm right at

00:01:52.400 --> 00:01:53.710
that point right there.

00:01:53.710 --> 00:01:58.000
So I'm at a boundary point
between solids and liquids at

00:01:58.000 --> 00:02:00.770
1 atmosphere of pressure,
right?

00:02:00.770 --> 00:02:04.550
This is when we're at 1
atmosphere of pressure.

00:02:04.550 --> 00:02:08.350
So this coincides with our
traditional notion of when ice

00:02:08.350 --> 00:02:10.979
freezes or when it melts
at 0 degrees.

00:02:10.979 --> 00:02:16.290
If we made the pressure
higher, what happens?

00:02:16.290 --> 00:02:20.340
Well, then ice starts melting at
a lower temperature, right?

00:02:20.340 --> 00:02:22.990
So this is pressure going up,
so pressure going up, let's

00:02:22.990 --> 00:02:24.400
say-- I don't know
what this is.

00:02:24.400 --> 00:02:29.290
This is maybe 10 atmospheres,
ten times Earth's atmospheric

00:02:29.290 --> 00:02:31.550
pressure at sea level, then
all of a sudden, the

00:02:31.550 --> 00:02:34.670
temperature at which solid
turns into liquid-- this

00:02:34.670 --> 00:02:37.750
transition is solid to liquid
--the temperature at which

00:02:37.750 --> 00:02:39.790
that happens will go down.

00:02:39.790 --> 00:02:42.480
Likewise, if we lower the
pressure, if we go to Denver

00:02:42.480 --> 00:02:45.820
and it's a mile high, pressure
is lower because we have less

00:02:45.820 --> 00:02:51.080
of the atmosphere above us,
then all of a sudden, the

00:02:51.080 --> 00:02:54.990
freezing point increases, so
the freezing point will be

00:02:54.990 --> 00:02:57.020
something above 1 degree.

00:02:57.020 --> 00:03:00.520
This isn't drawn completely to
scale, but the idea is your

00:03:00.520 --> 00:03:03.610
ice would actually freeze a
little bit faster and would

00:03:03.610 --> 00:03:08.740
freeze at a higher temperature
in Denver than it would at the

00:03:08.740 --> 00:03:15.840
bottom of the Dead Sea or in
Death Valley at some below sea

00:03:15.840 --> 00:03:18.210
level point on the planet.

00:03:18.210 --> 00:03:21.550
Now, this transition is
the transition between

00:03:21.550 --> 00:03:23.230
anything and gas.

00:03:23.230 --> 00:03:24.820
And we're very familiar,
this is 1 atmosphere.

00:03:24.820 --> 00:03:26.790
And remember, this is water
we're dealing with.

00:03:26.790 --> 00:03:29.520
This is the diagram for water,
so at 1 atmosphere, this is

00:03:29.520 --> 00:03:31.530
kind of the stuff that
we're used to seeing.

00:03:31.530 --> 00:03:33.910
Let me draw a line here.

00:03:33.910 --> 00:03:41.430
So at 1 atmosphere, 0 degrees is
where solid, or ice, turns

00:03:41.430 --> 00:03:42.780
into liquid water.

00:03:42.780 --> 00:03:45.670
And then we go up here, so we
keep going at a higher,

00:03:45.670 --> 00:03:48.680
higher, higher temperature, and
then here, this would be,

00:03:48.680 --> 00:03:54.550
since we're at 1 atmosphere,
this is 100 degrees Celsius

00:03:54.550 --> 00:03:55.480
right there.

00:03:55.480 --> 00:03:59.500
And that's the point at 1
atmosphere of pressure where

00:03:59.500 --> 00:04:02.850
liquid turns into gas,
or water vaporizes,

00:04:02.850 --> 00:04:04.030
or the liquid boils.

00:04:04.030 --> 00:04:07.020
All of those are acceptable
ways to think about that.

00:04:07.020 --> 00:04:08.760
But what happens when we
go to low pressure?

00:04:08.760 --> 00:04:11.680
Once again, let's take our
little trip to Denver.

00:04:11.680 --> 00:04:14.740
So that's Denver right there.

00:04:14.740 --> 00:04:15.970
It's not that drastic.

00:04:15.970 --> 00:04:19.500
I'm just doing that for
education purposes.

00:04:19.500 --> 00:04:25.030
Or even better, let's say Mount
Everest. Mount Everest,

00:04:25.030 --> 00:04:26.400
very low pressure there.

00:04:26.400 --> 00:04:29.120
Then our freezing point, we
already said that goes up when

00:04:29.120 --> 00:04:31.840
you lower the pressure, and your
boiling point goes down,

00:04:31.840 --> 00:04:36.040
so it's much easier to boil
something on the top of Mount

00:04:36.040 --> 00:04:39.870
Everest than it is to boil it at
the bottom or at the lowest

00:04:39.870 --> 00:04:43.740
point in Death Valley
or the Dead Sea.

00:04:43.740 --> 00:04:50.750
The intuition behind that is if
I have a liquid, a bunch of

00:04:50.750 --> 00:04:55.770
molecules in liquid form, and
they're touching each other,

00:04:55.770 --> 00:04:58.320
but they have enough kinetic
energy to move past each

00:04:58.320 --> 00:05:02.660
other, so they're flowing past
each other, they're kind of

00:05:02.660 --> 00:05:06.170
rubbing up against each other,
one of the reasons why they

00:05:06.170 --> 00:05:09.620
don't just evaporate, why this
guy doesn't just jump up

00:05:09.620 --> 00:05:10.910
there, is that there's
air above him.

00:05:10.910 --> 00:05:12.500
There's air pressure.

00:05:12.500 --> 00:05:14.570
And air pressure, we've
learned about this

00:05:14.570 --> 00:05:15.980
when we did PV nRT.

00:05:15.980 --> 00:05:19.430
That's a bunch of gas molecules,
and the pressure

00:05:19.430 --> 00:05:21.130
they're creating is essentially
caused by their

00:05:21.130 --> 00:05:22.660
temperature and their
kinetic energy.

00:05:22.660 --> 00:05:27.290
And they sit there, and they
bounce, and they essentially

00:05:27.290 --> 00:05:30.570
keep these heavier molecules
from going up.

00:05:30.570 --> 00:05:34.260
They keep them from essentially
separating from

00:05:34.260 --> 00:05:35.610
each other and turning
into a gas.

00:05:35.610 --> 00:05:39.380
So the more pressure you have,
the harder it is for these

00:05:39.380 --> 00:05:40.250
guys to escape.

00:05:40.250 --> 00:05:43.280
On the other hand, if we're in
a vacuum, if we're doing this

00:05:43.280 --> 00:05:46.120
on the surface of the moon and
there's none of these guys

00:05:46.120 --> 00:05:47.890
there, then just a little
slight bump.

00:05:47.890 --> 00:05:50.710
Even though this guy's still a
little bit attracted to over

00:05:50.710 --> 00:05:52.750
here, they're still attracted
to each other.

00:05:52.750 --> 00:05:54.980
But just a little bit of bump,
since there's no pressure up

00:05:54.980 --> 00:05:58.260
here on the surface of the moon,
might allow this guy to

00:05:58.260 --> 00:06:01.840
escape and go straight
to a gas.

00:06:01.840 --> 00:06:04.670
So when you lower the pressure,
it's just that much

00:06:04.670 --> 00:06:08.190
easier to go from liquid to gas
or even from solid to gas.

00:06:08.190 --> 00:06:09.670
And you might say, Sal,
that's a bizarre

00:06:09.670 --> 00:06:10.960
concept, solid to gas.

00:06:10.960 --> 00:06:14.260
It turns out, if you get to low
enough pressures here, I

00:06:14.260 --> 00:06:16.650
mean, let's say this is--
Actually, there's probably not

00:06:16.650 --> 00:06:17.020
stuff here.

00:06:17.020 --> 00:06:19.980
This is probably close to
a vacuum right here.

00:06:19.980 --> 00:06:23.000
You could go from ice-- So if
you took ice and you were on

00:06:23.000 --> 00:06:26.120
the moon and you were at the
right temperature-- this is

00:06:26.120 --> 00:06:29.800
maybe some negative degrees
Celsius temperature; I don't

00:06:29.800 --> 00:06:32.210
know what the exact temperature
is --your ice on

00:06:32.210 --> 00:06:36.280
the moon would go directly
from ice to a gas.

00:06:36.280 --> 00:06:38.850
Because there's this huge
vacuum here, so these

00:06:38.850 --> 00:06:41.520
molecules would say, hey,
there's all this space to fill

00:06:41.520 --> 00:06:43.290
and if they just get bumped a
little bit, they're just going

00:06:43.290 --> 00:06:45.230
to escape and turn into a gas.

00:06:45.230 --> 00:06:47.880
You might say, oh, Sal, that's
a strange phenomenon.

00:06:47.880 --> 00:06:49.380
It only exists on the moon.

00:06:49.380 --> 00:06:53.450
And to rebut that comment, I've
drawn the phase diagram

00:06:53.450 --> 00:06:54.700
for carbon dioxide.

00:06:58.260 --> 00:06:59.150
It's all around you.

00:06:59.150 --> 00:07:00.590
You're exhaling it
as we speak.

00:07:00.590 --> 00:07:03.950
Your plants in the room are
hopefully inhaling it, but

00:07:03.950 --> 00:07:06.900
carbon dioxide at 1 atmosphere
has a very different behavior

00:07:06.900 --> 00:07:07.930
than water.

00:07:07.930 --> 00:07:09.600
This is carbon dioxide
at 1 atmosphere.

00:07:09.600 --> 00:07:12.050
Just so you know, this
scale is definitely

00:07:12.050 --> 00:07:13.020
not drawn to scale.

00:07:13.020 --> 00:07:15.230
The difference between 1
atmosphere and 5 atmospheres

00:07:15.230 --> 00:07:18.170
is not the same as between
5 atmospheres and 73.

00:07:18.170 --> 00:07:21.530
Likewise, this is not
drawn to scale here.

00:07:21.530 --> 00:07:23.680
This is a much larger
distance than this.

00:07:23.680 --> 00:07:25.650
If I had to really draw it to
scale, I'd have to stretch

00:07:25.650 --> 00:07:27.180
this chart out or do a

00:07:27.180 --> 00:07:29.100
logarithmic chart or something.

00:07:29.100 --> 00:07:32.030
But anyway, I was talking
about carbon dioxide.

00:07:32.030 --> 00:07:36.340
So this is carbon dioxide solid,
and this is gas, and

00:07:36.340 --> 00:07:39.880
this is liquid carbon dioxide.

00:07:39.880 --> 00:07:46.120
So at 1 atmosphere, let's say
you live at sea level, like

00:07:46.120 --> 00:07:48.605
you're in New Orleans, I guess
that's a little bit below sea

00:07:48.605 --> 00:07:51.390
level-- that's where I grew up
--if you were able to get your

00:07:51.390 --> 00:07:55.560
fridge down to minus 80 degrees
Celsius, the carbon

00:07:55.560 --> 00:07:57.530
dioxide would actually freeze.

00:07:57.530 --> 00:07:59.820
And you're actually not too
unfamiliar with that, or at

00:07:59.820 --> 00:08:02.320
least you haven't been if you've
gone to some-- I don't

00:08:02.320 --> 00:08:05.870
know if they still use it for
smoke machines or for visual

00:08:05.870 --> 00:08:10.730
effects on stage, but
this is dry ice.

00:08:10.730 --> 00:08:14.820
It's frozen carbon dioxide.

00:08:14.820 --> 00:08:19.180
If you're at sea level
atmospheric pressure, as soon

00:08:19.180 --> 00:08:22.890
as you get above this minus 78
and 1/2 degrees Celsius, it

00:08:22.890 --> 00:08:24.990
sublimates to gas.

00:08:24.990 --> 00:08:28.560
So that process, where you go
straight from a solid to a

00:08:28.560 --> 00:08:29.810
gas, is sublimation.

00:08:33.260 --> 00:08:35.929
And that's why dry ice, when
you see it, you don't see

00:08:35.929 --> 00:08:39.000
liquid dry ice or you don't see
it at standard pressures.

00:08:39.000 --> 00:08:42.110
I've never seen liquid
carbon dioxide.

00:08:42.110 --> 00:08:45.590
In fact, to get liquid carbon
dioxide, you have to get above

00:08:45.590 --> 00:08:49.030
5 atmospheres so you have to get
above five times the sea

00:08:49.030 --> 00:08:50.900
level pressure on Earth, and
you're really not going to see

00:08:50.900 --> 00:08:52.670
that in natural conditions
on Earth.

00:08:52.670 --> 00:08:54.740
You might see that on Jupiter
or Saturn where you have

00:08:54.740 --> 00:08:57.330
tremendous pressures because of
the gravity and all of the

00:08:57.330 --> 00:08:59.710
atmosphere above you.

00:08:59.710 --> 00:09:01.680
Liquid carbon dioxide, you might
see-- I don't know if

00:09:01.680 --> 00:09:03.630
Jupiter actually has carbon, but
you'll probably see it on

00:09:03.630 --> 00:09:06.960
other huge massive planets
that are gas giants.

00:09:06.960 --> 00:09:10.380
But on Earth, this process is
just called sublimation.

00:09:10.380 --> 00:09:11.250
It's just a neat word.

00:09:11.250 --> 00:09:12.740
Or it's sublimating.

00:09:12.740 --> 00:09:15.460
It's going straight from solid
to gas and it's something

00:09:15.460 --> 00:09:16.920
you've seen with dry ice.

00:09:16.920 --> 00:09:18.820
Now, there's a couple other
interesting points here and

00:09:18.820 --> 00:09:20.920
you're probably already
noticing them.

00:09:20.920 --> 00:09:24.000
This right here is called the
triple point, because right

00:09:24.000 --> 00:09:27.480
here at this-- Well, in the case
of carbon dioxide, at 5

00:09:27.480 --> 00:09:32.130
atmospheres and minus 56 degrees
Celsius, the carbon

00:09:32.130 --> 00:09:36.960
dioxide is in a state of
equilibrium between the ice,

00:09:36.960 --> 00:09:38.540
the liquid and the gas.

00:09:38.540 --> 00:09:40.330
It's a little bit of
all of the three.

00:09:40.330 --> 00:09:43.030
And if you just nudge it in one
direction or another by

00:09:43.030 --> 00:09:44.550
nudging the pressure
or the temperature,

00:09:44.550 --> 00:09:46.450
it'll go in that direction.

00:09:46.450 --> 00:09:50.600
Similarly, water's triple
point is right here.

00:09:50.600 --> 00:09:52.380
It's at a much lower
pressure than we're

00:09:52.380 --> 00:09:53.270
used to dealing with.

00:09:53.270 --> 00:10:01.040
This is 0.611 kilopascals, or
just 611 pascals, which is

00:10:01.040 --> 00:10:03.500
5/1000 of an atmosphere.

00:10:03.500 --> 00:10:06.430
So if you go down to 5/1000 of
an atmosphere and you go a

00:10:06.430 --> 00:10:10.750
little bit above 0 degrees
Celsius, you're at the triple

00:10:10.750 --> 00:10:11.700
point of water.

00:10:11.700 --> 00:10:15.210
where water can take on any of
these states if you just nudge

00:10:15.210 --> 00:10:16.790
it in one direction
or another.

00:10:16.790 --> 00:10:18.730
Now, the other interesting
point on these

00:10:18.730 --> 00:10:20.680
charts is up here.

00:10:20.680 --> 00:10:22.710
This is the critical point.

00:10:22.710 --> 00:10:24.390
Sounds very important.

00:10:24.390 --> 00:10:25.440
Critical point.

00:10:25.440 --> 00:10:27.730
And that's the point at which
if you increase the

00:10:27.730 --> 00:10:31.190
temperature beyond that or the
pressure beyond that, you're

00:10:31.190 --> 00:10:35.140
dealing with a supercritical
fluid.

00:10:35.140 --> 00:10:37.030
It sounds very exciting.

00:10:37.030 --> 00:10:41.600
So above here, you have
a supercritical fluid.

00:10:41.600 --> 00:10:45.600
So very high temperature,
very high pressure.

00:10:45.600 --> 00:10:48.290
It's so high temperature that
it wants to be a gas, but

00:10:48.290 --> 00:10:49.930
you're putting so much pressure
on it that it wants

00:10:49.930 --> 00:10:52.060
to be a fluid, so it's
a little bit of both.

00:10:52.060 --> 00:10:55.270
And actually, in the case of
water, supercritical water is

00:10:55.270 --> 00:10:56.930
actually used as a solvent.

00:10:56.930 --> 00:10:59.800
Because you can imagine, it's
kind of like liquid water in

00:10:59.800 --> 00:11:02.210
that things can dissolve
in it, but it's so high

00:11:02.210 --> 00:11:05.300
temperature and it can diffuse
into solids that it's really

00:11:05.300 --> 00:11:08.440
good at just getting whatever
you want out of whatever

00:11:08.440 --> 00:11:15.490
you're trying to clean or
somehow get into or get salt

00:11:15.490 --> 00:11:16.850
put into the water.

00:11:16.850 --> 00:11:19.450
So this is supercritical
fluid and it's a fun

00:11:19.450 --> 00:11:20.190
thing to think about.

00:11:20.190 --> 00:11:24.150
But anyway, I just wanted to
expose you to these phase

00:11:24.150 --> 00:11:28.230
diagrams. Everything I've done
so far was at a constant

00:11:28.230 --> 00:11:30.140
pressure and I changed the
temperature, but you can also

00:11:30.140 --> 00:11:31.320
read them the other way.

00:11:31.320 --> 00:11:35.530
If I'm at 100 degrees, and I go
from-- Well, let's say I'm

00:11:35.530 --> 00:11:40.730
at 110 degrees, where at sea
level is comfortably in the

00:11:40.730 --> 00:11:44.590
gaseous phase for-- So this
is 110 degrees for water.

00:11:44.590 --> 00:11:45.650
It's water vapor.

00:11:45.650 --> 00:11:48.890
But if I were to increase the
pressure and I keep increasing

00:11:48.890 --> 00:11:51.730
the pressure and maybe I dig a
hole or something or I go into

00:11:51.730 --> 00:11:58.120
the ocean, then it's going to
condense into water or it's

00:11:58.120 --> 00:11:59.260
going to condense
into a liquid.

00:11:59.260 --> 00:12:06.550
If I did that experiment here,
when I increase the pressure,

00:12:06.550 --> 00:12:09.500
I'm going to reverse
sublimate.

00:12:09.500 --> 00:12:11.710
And I think I wrote down a
word for what that is.

00:12:11.710 --> 00:12:12.980
Let me see if I wrote
it down someplace.

00:12:12.980 --> 00:12:13.840
Oh, no, I didn't.

00:12:13.840 --> 00:12:14.980
I didn't write it down.

00:12:14.980 --> 00:12:19.210
But essentially it's something
like condense, but the word is

00:12:19.210 --> 00:12:20.480
escaping me at the second.

00:12:20.480 --> 00:12:21.770
It's something on the word of

00:12:21.770 --> 00:12:23.520
condensing or falling together.

00:12:23.520 --> 00:12:27.290
Anyway, I forget the word, but
it'll go straight from a gas

00:12:27.290 --> 00:12:28.270
to a solid.

00:12:28.270 --> 00:12:30.110
So these are pretty neat
diagrams. They actually tell a

00:12:30.110 --> 00:12:32.830
lot about different substances
and then tell you what happens

00:12:32.830 --> 00:12:35.450
when the pressure or the
temperature changes.


Chilling water problem

WEBVTT
Kind: captions
Language: en

00:00:00.510 --> 00:00:03.990
Let's do another states of
matter phase change problem.

00:00:03.990 --> 00:00:05.280
And we'll deal with
water again.

00:00:05.280 --> 00:00:08.340
But this one hopefully will
stretch our neurons a little

00:00:08.340 --> 00:00:09.360
bit further.

00:00:09.360 --> 00:00:12.205
So let's say I have 500
grams of water.

00:00:14.990 --> 00:00:20.710
Of liquid water.

00:00:20.710 --> 00:00:25.420
At 60 degrees Celsius.

00:00:25.420 --> 00:00:29.170
Now my goal is to get it to
zero degrees Celsius.

00:00:29.170 --> 00:00:32.670
And the way I'm going to do it
is, I'm going to put ice into

00:00:32.670 --> 00:00:34.480
this 500 grams of water.

00:00:34.480 --> 00:00:39.070
And my ice machine at home makes
ice that comes out of

00:00:39.070 --> 00:00:44.480
the machine at minus 10
degrees Celsius ice.

00:00:44.480 --> 00:00:48.710
And my question is, exactly
how much ice do I need?

00:00:48.710 --> 00:00:51.690
So how much, or how
many grams of ice?

00:00:57.820 --> 00:01:00.140
And I'm going to take the ice
out of the freezer and just

00:01:00.140 --> 00:01:01.490
plop it into my liquid.

00:01:01.490 --> 00:01:05.890
How much do I need to bring this
liquid, this 500 grams of

00:01:05.890 --> 00:01:10.870
liquid water, down
to zero degrees?

00:01:10.870 --> 00:01:13.970
So the idea, if we just
imagine a cup here.

00:01:13.970 --> 00:01:15.800
Let me draw a cup.

00:01:15.800 --> 00:01:17.270
This is a cup.

00:01:17.270 --> 00:01:21.130
I have some 60 degree
water in there.

00:01:21.130 --> 00:01:24.580
I'm going to plunk a big
chunk of ice in there.

00:01:27.460 --> 00:01:31.350
And what's going to happen is
that heat from the water is

00:01:31.350 --> 00:01:32.250
going to go into the ice.

00:01:32.250 --> 00:01:38.140
So the ice is going to absorb
heat from the water.

00:01:38.140 --> 00:01:40.890
So in order for water to go
from 60 degrees to zero

00:01:40.890 --> 00:01:43.040
degrees, I have to extract
heat out of it.

00:01:43.040 --> 00:01:45.260
And we're about to figure
out just how much heat.

00:01:45.260 --> 00:01:47.620
And so we have to say, whatever
was extracted out of

00:01:47.620 --> 00:01:50.760
the water, essentially has to
be contained by the ice.

00:01:50.760 --> 00:01:53.320
And the ice can't get
above zero degrees.

00:01:53.320 --> 00:01:56.150
Essentially, that amount of
ice has to absorb all that

00:01:56.150 --> 00:01:58.180
heat to go from minus
10 to zero.

00:01:58.180 --> 00:02:01.780
And then also, that energy will
be used to melt it a bit.

00:02:01.780 --> 00:02:04.230
But if we don't have enough ice,
then the ice is going to

00:02:04.230 --> 00:02:06.310
go beyond that and then
warm up even more.

00:02:06.310 --> 00:02:08.009
So let's see how we do this.

00:02:08.009 --> 00:02:11.380
So how much energy do we have
to take out of the 500 grams

00:02:11.380 --> 00:02:12.680
of liquid water?

00:02:12.680 --> 00:02:14.570
Well, it's the same amount of
energy that it would take to

00:02:14.570 --> 00:02:16.540
put into zero degrees
liquid water and

00:02:16.540 --> 00:02:18.150
get it to 60 degrees.

00:02:18.150 --> 00:02:21.180
So we're talking about
a 50 degree change.

00:02:21.180 --> 00:02:29.150
So the energy or the heat out
of the water is going to be

00:02:29.150 --> 00:02:46.060
the specific heat of water,
4.178 joules per grams Kelvin.

00:02:46.060 --> 00:02:49.330
And I have to multiply that
times the number of grams of

00:02:49.330 --> 00:02:52.090
water I have to cool down, I
have to take the heat out of.

00:02:52.090 --> 00:02:57.330
And we know that's 500 grams.
And then I multiply that times

00:02:57.330 --> 00:02:59.680
the temperature differential
that we care about.

00:02:59.680 --> 00:03:02.260
And just a side note, I use
this specific heat because

00:03:02.260 --> 00:03:03.560
we're dealing with
liquid water.

00:03:06.680 --> 00:03:08.540
Liquid water going
from 60 to zero.

00:03:08.540 --> 00:03:10.590
So the final thing, I have to
multiply it by the change in

00:03:10.590 --> 00:03:11.050
temperature.

00:03:11.050 --> 00:03:13.350
The change in temperature
is 60 degrees.

00:03:13.350 --> 00:03:18.450
Times 60 degrees.

00:03:18.450 --> 00:03:21.410
There's a little button on the
side of my pen, when I press

00:03:21.410 --> 00:03:23.900
it by accident sometimes it
does that weird thing.

00:03:23.900 --> 00:03:26.110
So let's see what this is.

00:03:26.110 --> 00:03:37.780
So this is 4.178 times 500 times
change of 60 degrees.

00:03:37.780 --> 00:03:40.040
It could be a change of 60
degrees Kelvin or a change of

00:03:40.040 --> 00:03:40.960
60 degrees Celsius.

00:03:40.960 --> 00:03:41.600
It doesn't matter.

00:03:41.600 --> 00:03:44.100
The actual difference is the
same, whether we're doing

00:03:44.100 --> 00:03:45.840
Kelvin or Celsius.

00:03:45.840 --> 00:03:57.130
And it's 125,340 joules.

00:03:57.130 --> 00:03:59.340
So this is the amount of heat
that you have to take out of

00:03:59.340 --> 00:04:02.450
60 degree water in order to get
it down to zero degrees.

00:04:02.450 --> 00:04:06.110
Or the amount of heat you have
to add to zero degree water to

00:04:06.110 --> 00:04:07.920
get it to 60 degrees.

00:04:07.920 --> 00:04:14.300
So essentially, our ice has
to absorb this much energy

00:04:14.300 --> 00:04:16.779
without going above
zero degrees.

00:04:16.779 --> 00:04:20.060
So how much energy can
the ice absorb?

00:04:20.060 --> 00:04:21.149
Well let's set a variable.

00:04:21.149 --> 00:04:22.940
The question is how much ice.

00:04:22.940 --> 00:04:27.350
So let's set our variable,
maybe we'll call it I.

00:04:27.350 --> 00:04:30.370
Let's do x. x is always
the unknown variable.

00:04:30.370 --> 00:04:37.030
So we're going to have
x grams of ice.

00:04:37.030 --> 00:04:39.960
OK, and it starts at
minus 10 degrees.

00:04:39.960 --> 00:04:45.530
So when this x grams of ice
warms from minus 10 degrees to

00:04:45.530 --> 00:04:49.405
zero degrees Celsius, how much
energy will it be absorbing?

00:04:52.040 --> 00:04:58.140
So to go from minus 10 degrees
Celsius to zero degrees

00:04:58.140 --> 00:05:02.450
Celsius, the heat that's
absorbed by the ice is equal

00:05:02.450 --> 00:05:11.420
to-- is equal to the specific
heat of ice, ice water, 2.05

00:05:11.420 --> 00:05:19.690
joules per gram Kelvin, times
the amount of ice.

00:05:19.690 --> 00:05:20.830
That's what we're solving for.

00:05:20.830 --> 00:05:23.050
So times x.

00:05:23.050 --> 00:05:25.150
Times the change
in temperature.

00:05:25.150 --> 00:05:28.230
So this is a 10 degree change
in Celsius degrees, which is

00:05:28.230 --> 00:05:31.090
also a 10 degree change
in Kelvin degrees.

00:05:31.090 --> 00:05:32.730
We can just do 10 degrees.

00:05:32.730 --> 00:05:35.850
I could write Kelvin here, just
because at least when I

00:05:35.850 --> 00:05:38.670
wrote the specific heat units,
I have a Kelvin in the

00:05:38.670 --> 00:05:38.840
denominator.

00:05:38.840 --> 00:05:40.760
It could have been a Celsius,
but just to

00:05:40.760 --> 00:05:41.960
make them cancel out.

00:05:41.960 --> 00:05:44.880
This is, of course, x grams.
So the grams cancel out.

00:05:44.880 --> 00:05:48.440
So that heat absorbed to go from
minus 10 degree ice to

00:05:48.440 --> 00:05:55.220
zero degree ice is 2.05
times 10 is 20.5.

00:05:55.220 --> 00:06:03.890
So it's 20.5 times x joules.

00:06:03.890 --> 00:06:06.550
This is to go from minus 10
degrees to zero degrees.

00:06:06.550 --> 00:06:08.780
Now, once we're at zero degrees,
the ice can even

00:06:08.780 --> 00:06:12.120
absorb more energy before
increasing in

00:06:12.120 --> 00:06:13.980
temperature as it melts.

00:06:13.980 --> 00:06:17.950
Remember, when I drew that
phase change diagram.

00:06:17.950 --> 00:06:20.250
The ice gains some energy
and then it

00:06:20.250 --> 00:06:22.260
levels out as it melts.

00:06:22.260 --> 00:06:26.720
As the the bonds, the hydrogen
bonds start sliding past each

00:06:26.720 --> 00:06:29.360
other, and the crystalline
structure breaks down.

00:06:29.360 --> 00:06:30.540
So this is the amount
of energy the

00:06:30.540 --> 00:06:31.790
ice can also absorb.

00:06:34.815 --> 00:06:36.880
Let me do it in a
different color.

00:06:36.880 --> 00:06:42.430
Zero degree ice to zero--
I did it again--

00:06:42.430 --> 00:06:43.983
to zero degree water.

00:06:46.960 --> 00:06:51.680
Well the heat absorbed now
is going to be the heat

00:06:51.680 --> 00:06:53.300
of fusion of ice.

00:06:53.300 --> 00:06:55.510
Or the melting heat,
either one.

00:06:55.510 --> 00:06:59.730
That's 333 joules per gram.

00:06:59.730 --> 00:07:05.760
It's equal to 333.55 joules per
gram times the number of

00:07:05.760 --> 00:07:08.090
grams we have. Once
again, that's x

00:07:08.090 --> 00:07:09.770
grams. They cancel out.

00:07:09.770 --> 00:07:18.580
So the ice will absorb 333.55
joules as it goes from zero

00:07:18.580 --> 00:07:22.510
degree ice to zero
degree water.

00:07:22.510 --> 00:07:25.453
Or 333.55x joules.

00:07:25.453 --> 00:07:27.690
Let me put the x there,
that's key.

00:07:27.690 --> 00:07:30.970
So the total amount of heat
that the ice can absorb

00:07:30.970 --> 00:07:32.660
without going above
zero degrees.

00:07:32.660 --> 00:07:35.100
Because once it's at zero degree
water, as you put more

00:07:35.100 --> 00:07:38.800
heat into it, it's going to
start getting warmer again.

00:07:38.800 --> 00:07:41.080
If the ice gets above zero
degrees, there's no way it's

00:07:41.080 --> 00:07:43.020
going to bring the water
down to zero degrees.

00:07:46.040 --> 00:07:48.340
The water can't get above
zero degrees.

00:07:48.340 --> 00:07:51.280
So how much total heat
can our ice absorb?

00:07:51.280 --> 00:07:56.440
So heat absorbed is equal to the
heat it can absorb when it

00:07:56.440 --> 00:07:59.400
goes from minus 10 to
zero degrees ice.

00:07:59.400 --> 00:08:02.950
And that's 20.5x.

00:08:02.950 --> 00:08:06.950
Where x is the number of grams
of ice we have. Plus the

00:08:06.950 --> 00:08:09.970
amount of heat we can absorb as
we go from zero degree ice

00:08:09.970 --> 00:08:11.600
to zero degree water.

00:08:11.600 --> 00:08:16.155
And that's 333.55x.

00:08:16.155 --> 00:08:17.500
And of course, all of
this is joules.

00:08:17.500 --> 00:08:20.860
So this is the total amount of
heat that the ice can absorb

00:08:20.860 --> 00:08:24.270
without going above
zero degrees.

00:08:24.270 --> 00:08:26.520
Now, how much real energy
does it have to absorb?

00:08:26.520 --> 00:08:32.289
Well it has to absorb all of
this 125,340 joules of energy

00:08:32.289 --> 00:08:33.070
out of the water.

00:08:33.070 --> 00:08:35.360
Because that's the amount of
energy we have to extract from

00:08:35.360 --> 00:08:38.120
the water to bring it down
to zero degrees.

00:08:38.120 --> 00:08:42.820
So the amount of energy
the ice absorbs

00:08:42.820 --> 00:08:46.690
has to be this 125,340.

00:08:46.690 --> 00:08:53.200
So that has to be equal
to 125,340 joules.

00:08:53.200 --> 00:08:55.380
We can do a little bit
of algebra here.

00:08:55.380 --> 00:08:56.640
Add these two things.

00:08:56.640 --> 00:09:10.670
20.5x plus 333.55x is 354.05x.

00:09:10.670 --> 00:09:11.470
Is that right?

00:09:11.470 --> 00:09:14.370
Yeah, 330 plus 30 is 350.

00:09:14.370 --> 00:09:16.310
Then you have a 3 with
a 0.5 there.

00:09:16.310 --> 00:09:20.960
354.05x and that is equal to the
amount of energy we take

00:09:20.960 --> 00:09:22.500
out of the water.

00:09:22.500 --> 00:09:23.750
You divide both sides.

00:09:23.750 --> 00:09:31.590
So x is equal to 125,340
divided by 354.05.

00:09:31.590 --> 00:09:33.210
I'll take out the calculator
for this.

00:09:37.210 --> 00:09:43.010
The calculator tells me 125,340,
the amount of energy

00:09:43.010 --> 00:09:53.770
that has to be absorbed by the
ice, divided by 354.05 is

00:09:53.770 --> 00:09:58.960
equal to 354 grams. Roughly;
there's a little bit extra.

00:09:58.960 --> 00:10:01.700
So actually, just to be careful
maybe I'll take 355

00:10:01.700 --> 00:10:02.360
grams of ice.

00:10:02.360 --> 00:10:05.020
Because I definitely want
my water to be chilled.

00:10:05.020 --> 00:10:12.980
So our answer is x is equal
to 354.02 grams of ice.

00:10:12.980 --> 00:10:13.900
So this is interesting.

00:10:13.900 --> 00:10:16.860
I had 500 grams of liquid.

00:10:16.860 --> 00:10:19.120
And you know, intuitively I
said, well if I have to bring

00:10:19.120 --> 00:10:22.660
that down to zero degrees, I'd
have to have a ton of ice.

00:10:22.660 --> 00:10:27.220
But it turns out, I only need,
what was the exact number?

00:10:27.220 --> 00:10:31.960
So the liquid is 500 grams.
About, roughly half a pound,

00:10:31.960 --> 00:10:33.930
if you want to get a sense for
how much 500 grams is.

00:10:33.930 --> 00:10:36.920
A kilogram is 2.2 pounds.

00:10:36.920 --> 00:10:39.080
So this ice is 354.

00:10:39.080 --> 00:10:42.010
So you actually have to have
less ice than water.

00:10:42.010 --> 00:10:44.220
Which is interesting, because
it seems like the ice isn't

00:10:44.220 --> 00:10:45.760
making that big of a
temperature change.

00:10:45.760 --> 00:10:48.650
The ice is only going from
minus 10 to zero degrees.

00:10:48.650 --> 00:10:51.870
While the water is going all
the way from 60 degrees to

00:10:51.870 --> 00:10:52.570
zero degrees.

00:10:52.570 --> 00:10:54.130
So you're like, how does
that work out?

00:10:54.130 --> 00:10:57.340
And the reason is because so
much energy can be absorbed by

00:10:57.340 --> 00:11:02.410
the ice in the form of potential
energy as it melts.

00:11:02.410 --> 00:11:04.740
So if you talk about all the
energy that the ice is

00:11:04.740 --> 00:11:06.910
asborbing, most of it is
due to the heat of

00:11:06.910 --> 00:11:09.920
fusion right there.

00:11:09.920 --> 00:11:12.630
You can actually have zero
degree ice and it can still

00:11:12.630 --> 00:11:17.020
absorb this huge amount of
energy just by melting it.

00:11:17.020 --> 00:11:19.140
Without even changing
its temperature.

00:11:19.140 --> 00:11:22.700
Anyway, hopefully you found
that reasonably useful.


Specific heat, heat of fusion and vaporization example

WEBVTT
Kind: captions
Language: en

00:00:00.410 --> 00:00:02.970
A couple of videos ago, we
learned that if we started

00:00:02.970 --> 00:00:06.850
with solid water or ice at a
reasonably low temperature--

00:00:06.850 --> 00:00:08.160
maybe this temperature
right here is

00:00:08.160 --> 00:00:10.380
minus 10 degrees Celsius.

00:00:10.380 --> 00:00:12.670
And we can deal with Celsius
when we're dealing with these

00:00:12.670 --> 00:00:14.610
phase changes, because we really
just care about the

00:00:14.610 --> 00:00:16.930
difference in temperature, and
not necessarily the absolute

00:00:16.930 --> 00:00:17.670
temperature.

00:00:17.670 --> 00:00:22.450
So one degree in Celsius is the
same thing is one degree

00:00:22.450 --> 00:00:24.680
in Kelvin so the differences
are the same whether you're

00:00:24.680 --> 00:00:26.300
dealing with Celsius
or Kelvin.

00:00:26.300 --> 00:00:29.640
So we're starting with minus
10 degree Celsius

00:00:29.640 --> 00:00:32.770
ice or solid water.

00:00:32.770 --> 00:00:35.420
And we learned that as you heat
it up, as you add heat

00:00:35.420 --> 00:00:38.170
energy to the water, the
temperature goes up.

00:00:38.170 --> 00:00:40.940
The molecules, at least while
they're in that ice lattice

00:00:40.940 --> 00:00:42.840
network, they just
start vibrating.

00:00:42.840 --> 00:00:46.510
And their average kinetic energy
goes up until we get to

00:00:46.510 --> 00:00:47.980
zero degrees.

00:00:47.980 --> 00:00:50.670
Which is the melting
point of water.

00:00:50.670 --> 00:00:52.620
And at zero degrees, we already
learned something

00:00:52.620 --> 00:00:53.910
interesting happens.

00:00:53.910 --> 00:00:56.990
The added heat in the system
does not increase the

00:00:56.990 --> 00:00:59.440
temperature of the
ice anymore.

00:00:59.440 --> 00:01:01.720
At least over that little
period right here.

00:01:01.720 --> 00:01:05.019
What's happening is that heat
energy is being used to kind

00:01:05.019 --> 00:01:06.620
of break the lattice
structure.

00:01:06.620 --> 00:01:08.440
To add potential energy
to the ice.

00:01:08.440 --> 00:01:10.080
Or essentially melt it.

00:01:10.080 --> 00:01:14.350
So for it here, right
here, we're ice.

00:01:14.350 --> 00:01:17.010
Right at this point, we're
zero degree ice.

00:01:17.010 --> 00:01:20.110
And then as we add more and
more heat we get to zero

00:01:20.110 --> 00:01:21.270
degree water.

00:01:21.270 --> 00:01:24.590
So at zero degrees, you can
either have water or ice.

00:01:24.590 --> 00:01:26.960
And if you have water, to turn
it into ice, you have to take

00:01:26.960 --> 00:01:28.090
heat out of it.

00:01:28.090 --> 00:01:30.470
And if you have ice, and you
want to turn it into water,

00:01:30.470 --> 00:01:31.830
you have to put heat into it.

00:01:31.830 --> 00:01:34.910
And then the heat is used
again to warm up the

00:01:34.910 --> 00:01:36.490
water at some rate.

00:01:36.490 --> 00:01:40.310
And then at 100 degrees, which
is the boiling point of water,

00:01:40.310 --> 00:01:44.480
right here, a similar phase
change happens.

00:01:44.480 --> 00:01:47.200
Where the increased heat is
not used to increase the

00:01:47.200 --> 00:01:51.150
temperature of the water, it's
used to put potential energy

00:01:51.150 --> 00:01:52.150
into the system.

00:01:52.150 --> 00:01:55.900
So the water molecules are
forced away from each other.

00:01:55.900 --> 00:01:58.260
The same way that if I'm forced
away from the planet

00:01:58.260 --> 00:02:00.280
Earth, I have potential
energy because I can

00:02:00.280 --> 00:02:01.770
fall back to the earth.

00:02:01.770 --> 00:02:03.820
Similarly, they have the
potential energy of falling

00:02:03.820 --> 00:02:05.100
back to each other.

00:02:05.100 --> 00:02:07.970
But this energy, right here
is the energy necessary to

00:02:07.970 --> 00:02:09.169
vaporize the water.

00:02:09.169 --> 00:02:13.800
Right here you have 100 degree
water, 100 degree liquid.

00:02:13.800 --> 00:02:17.150
And here you have 100 degree
vapor, water vapor.

00:02:17.150 --> 00:02:19.970
And then as you add more and
more heat, once again it

00:02:19.970 --> 00:02:21.120
increases the temperature.

00:02:21.120 --> 00:02:24.560
But you, Sal, I already learned
this a few videos ago,

00:02:24.560 --> 00:02:26.030
I have the intuition.

00:02:26.030 --> 00:02:27.710
But I want to deal with
real numbers.

00:02:27.710 --> 00:02:30.310
I want to know exactly how
much heat is required for

00:02:30.310 --> 00:02:32.090
these different things
to happen.

00:02:32.090 --> 00:02:35.900
And for that, we can
get these numbers.

00:02:35.900 --> 00:02:39.120
And these are specific to the
different states of water.

00:02:39.120 --> 00:02:42.460
If you looked up any other
element or molecule, you would

00:02:42.460 --> 00:02:45.100
have different values for these
numbers we're going to

00:02:45.100 --> 00:02:46.510
be dealing with right now.

00:02:46.510 --> 00:02:49.400
But this first number right here
is the heat of fusion.

00:02:49.400 --> 00:02:53.000
And this is the amount of heat
that's required to fuse 100

00:02:53.000 --> 00:02:57.250
degree water into
100 degree ice.

00:02:57.250 --> 00:02:59.160
Or the amount of energy you have
to take out of the water.

00:02:59.160 --> 00:03:02.130
So this distance right
here, or along this

00:03:02.130 --> 00:03:06.140
axis, is 333 joules.

00:03:06.140 --> 00:03:08.320
If you're going in the the
leftward direction, you have

00:03:08.320 --> 00:03:11.000
to take that much out of the
system to turn into ice.

00:03:11.000 --> 00:03:12.850
If you're going in the rightward
direction, you have

00:03:12.850 --> 00:03:14.600
to add that much to
turn into water.

00:03:14.600 --> 00:03:15.910
So heat of fusion.

00:03:15.910 --> 00:03:17.900
It's called the heat of fusion
because when you fuse

00:03:17.900 --> 00:03:19.350
something together you
make it solid.

00:03:19.350 --> 00:03:21.990
So it could also be considered
the heat of melting.

00:03:21.990 --> 00:03:24.280
Just two different words for the
same, thing depending on

00:03:24.280 --> 00:03:25.220
what direction you going.

00:03:25.220 --> 00:03:28.500
The important thing is
the number, 333.

00:03:28.500 --> 00:03:31.860
Similarly, you have the
heat of vaporization.

00:03:31.860 --> 00:03:38.800
2257 joules per gram.

00:03:38.800 --> 00:03:42.420
That's this distance along
this axis right here.

00:03:42.420 --> 00:03:47.040
So if you had one gram of 100
degree liquid water and you

00:03:47.040 --> 00:03:49.750
wanted to turn it into
one gram of 100

00:03:49.750 --> 00:03:51.200
degree liquid vapor.

00:03:51.200 --> 00:03:54.620
And in all of this, we're
assuming that nothing silly is

00:03:54.620 --> 00:03:55.770
happening to the pressure,
that we're

00:03:55.770 --> 00:03:57.010
under constant pressure.

00:03:57.010 --> 00:04:01.830
You would have to put 2257
joules into the system.

00:04:01.830 --> 00:04:04.660
If you had 100 degree vapor and
you wanted to condense it,

00:04:04.660 --> 00:04:08.210
you would have to take that much
energy out of the system.

00:04:08.210 --> 00:04:11.080
OK, fine, you know how much
energy is required for the

00:04:11.080 --> 00:04:11.810
phase changes.

00:04:11.810 --> 00:04:14.330
But what about these
parts right here?

00:04:14.330 --> 00:04:21.250
How much energy is required to
warm up a gram of ice by one

00:04:21.250 --> 00:04:23.030
degree Celsius or Kelvin?

00:04:23.030 --> 00:04:26.720
And for that we look at
the specific heat.

00:04:26.720 --> 00:04:32.010
It takes 2 joules of
energy to warm up 1

00:04:32.010 --> 00:04:34.880
gram 1 degree Kelvin.

00:04:34.880 --> 00:04:36.800
When water is in the
solid state.

00:04:36.800 --> 00:04:39.460
When it's in the liquid state,
it takes about double that.

00:04:39.460 --> 00:04:42.210
It takes about 4 joules
per gram to

00:04:42.210 --> 00:04:44.080
raise it 1 degree Kelvin.

00:04:44.080 --> 00:04:45.660
And when you're in the vapor
state, it's actually more

00:04:45.660 --> 00:04:49.020
similar to the solid state.

00:04:49.020 --> 00:04:52.920
So given what we know now, we
can actually figure out how

00:04:52.920 --> 00:05:04.120
much energy it would take to go
from minus 10 degree ice to

00:05:04.120 --> 00:05:07.600
110 degree vapor.

00:05:07.600 --> 00:05:09.380
Let's work this out.

00:05:09.380 --> 00:05:11.200
So the first thing we're going
to be doing is, we're going to

00:05:11.200 --> 00:05:17.025
be going from minus 10 degree
ice to zero degree ice.

00:05:19.640 --> 00:05:21.110
So we're going to
go 10 degrees.

00:05:21.110 --> 00:05:24.090
We have to figure out how much
heat does it take to warm up

00:05:24.090 --> 00:05:25.850
ice by 10 degrees.

00:05:25.850 --> 00:05:29.360
So the heat is going to be
equal to the change in

00:05:29.360 --> 00:05:30.470
temperature.

00:05:30.470 --> 00:05:35.110
So actually let me write the
specific heat first. So 2.05

00:05:35.110 --> 00:05:37.160
joules per gram Kelvin.

00:05:45.880 --> 00:05:49.000
Oh, and I should tell you, we
can't different values for the

00:05:49.000 --> 00:05:51.400
amount of ice we're warming up
to vapor, so let's say we're

00:05:51.400 --> 00:05:54.390
dealing with 200 grams.

00:05:54.390 --> 00:05:58.060
So it'll be the specific heat
times the number of grams

00:05:58.060 --> 00:06:01.900
we're warming up of ice times
the change in temperature that

00:06:01.900 --> 00:06:02.660
we're trying to get.

00:06:02.660 --> 00:06:06.610
So, times 10 degrees Kelvin.

00:06:06.610 --> 00:06:08.480
Le'ts just say it's a 10 degrees
Kelvin change, it

00:06:08.480 --> 00:06:10.170
doesn't matter if we're using
Kelvin or Celsius.

00:06:10.170 --> 00:06:12.750
I could have written
a Celsius here.

00:06:12.750 --> 00:06:15.180
Let's put Celsius right there.

00:06:15.180 --> 00:06:16.750
So what is that equal to?

00:06:16.750 --> 00:06:19.070
Get the calculator.

00:06:19.070 --> 00:06:21.130
Clear it out.

00:06:21.130 --> 00:06:40.625
2.05 times 200 times times 10
is equal to 4,100 joules.

00:06:40.625 --> 00:06:42.690
Let me do this in a
different color.

00:06:42.690 --> 00:06:46.810
This is 4,100 joules.

00:06:46.810 --> 00:06:47.770
Fair enough.

00:06:47.770 --> 00:06:50.300
Now, so what we've done is just
this part right here.

00:06:50.300 --> 00:06:54.620
This distance right here
is 4,100 joules.

00:06:54.620 --> 00:06:56.870
Now we have to turn that
zero degree ice

00:06:56.870 --> 00:06:58.120
into zero degree water.

00:07:07.560 --> 00:07:10.850
And for that we use the
heat of fusion.

00:07:10.850 --> 00:07:12.900
We're adding that
amount of heat.

00:07:12.900 --> 00:07:20.030
It's 333.5 joules per gram.

00:07:20.030 --> 00:07:27.530
So that's equal to 335.55 joules
per gram times, we have

00:07:27.530 --> 00:07:30.880
200 grams of ice that we're
trying to melt.

00:07:30.880 --> 00:07:32.700
So that is what?

00:07:32.700 --> 00:07:34.940
So let me get the
calculator out.

00:07:34.940 --> 00:07:49.280
So I have 335.55 times 200
is equal to 67,110.

00:07:49.280 --> 00:07:52.150
Let me do it in that color so
can sum them up at the end.

00:07:52.150 --> 00:07:58.640
67,110 joules to
melt the water.

00:07:58.640 --> 00:07:59.860
Or take it from ice to water.

00:07:59.860 --> 00:08:02.310
Now, we have to go from, and
this is the big one.

00:08:02.310 --> 00:08:09.480
We have to go from zero degree
water to 100 degree water.

00:08:09.480 --> 00:08:11.000
Or liquid water.

00:08:11.000 --> 00:08:12.780
This is in the liquid state.

00:08:12.780 --> 00:08:22.210
So now we take the specific heat
of water which was 4.178.

00:08:22.210 --> 00:08:24.160
For some reason I'm thinking
it's 4.176

00:08:24.160 --> 00:08:24.960
but it doesn't matter.

00:08:24.960 --> 00:08:28.540
So it's 4.178.

00:08:28.540 --> 00:08:31.640
I might off a little bit on that
number, but that digit is

00:08:31.640 --> 00:08:32.720
not that significant.

00:08:32.720 --> 00:08:38.299
Joules per gram Celsius
times 200 grams

00:08:38.299 --> 00:08:42.929
times 100 degrees Celsius.

00:08:42.929 --> 00:08:45.450
And notice, the Celsius and
the Celsius cancel out.

00:08:45.450 --> 00:08:47.010
The grams and the grams
cancel out.

00:08:47.010 --> 00:08:49.520
So we are left with joules,
which is what we want.

00:08:49.520 --> 00:08:52.140
We want to know how much heat
or how much energy we're

00:08:52.140 --> 00:08:54.140
adding to the system.

00:08:54.140 --> 00:08:56.010
Let me get the calculator out.

00:08:56.010 --> 00:09:11.970
So this stage is going to be
4.178 times 200 times 100 is

00:09:11.970 --> 00:09:35.240
equal to 83,560 joules.

00:09:35.240 --> 00:09:36.230
Does that look about right?

00:09:36.230 --> 00:09:36.490
Let's see.

00:09:36.490 --> 00:09:41.650
4 times 200 is 800, 800 times
100; yeah, that's about right.

00:09:41.650 --> 00:09:45.150
Now, we're dealing with 100
degree water vapor, and we

00:09:45.150 --> 00:09:51.250
have to turn that 100
degree water vapor

00:09:51.250 --> 00:09:55.410
to 110 degree vapor.

00:09:55.410 --> 00:09:58.140
So we use the specific
heat of vapor.

00:09:58.140 --> 00:10:06.980
1.89 joules per gram Kelvin.

00:10:06.980 --> 00:10:09.790
Multiplied by the amount of
vapor we're dealing with, 200

00:10:09.790 --> 00:10:11.290
grams. That obviously
doesn't change.

00:10:11.290 --> 00:10:14.900
We're not adding or taking away
mass from the system.

00:10:14.900 --> 00:10:18.280
Times the temperature
change, times 10.

00:10:18.280 --> 00:10:19.180
So what is that?

00:10:19.180 --> 00:10:22.750
Let me get the calculator
out again.

00:10:22.750 --> 00:10:25.590
So we're dealing with
a 10 degree change.

00:10:25.590 --> 00:10:43.270
10 degree Celsius times 200
times 1.89 is equal to 3,780.

00:10:43.270 --> 00:10:45.385
And I just realized, I made
a horrible mistake.

00:10:48.530 --> 00:10:51.090
It's not an irrevocable mistake,
otherwise I would

00:10:51.090 --> 00:10:52.330
rerecord the video.

00:10:52.330 --> 00:10:54.530
But I just figured out the
amount of energy to take it

00:10:54.530 --> 00:10:58.020
from zero degree water to 100
degree water, which is this

00:10:58.020 --> 00:11:00.720
energy right here.

00:11:00.720 --> 00:11:04.000
And now I just calculated how
much energy to go from 100

00:11:04.000 --> 00:11:06.970
degree vapor to 110
degree vapor.

00:11:06.970 --> 00:11:09.470
Which is this right here, that
distance right here.

00:11:09.470 --> 00:11:11.680
I forgot to figure out how much
energy to turn that 100

00:11:11.680 --> 00:11:14.440
degree water into 100
degree vapor.

00:11:14.440 --> 00:11:16.000
So that's key.

00:11:16.000 --> 00:11:19.440
So I really should have done
that up here before I

00:11:19.440 --> 00:11:20.360
calculated the vapor.

00:11:20.360 --> 00:11:21.720
But I'll do it down here.

00:11:21.720 --> 00:11:30.600
So to do 100 degree water
to 100 degree vapor.

00:11:30.600 --> 00:11:33.580
That's this step right here,
this is the phase change.

00:11:33.580 --> 00:11:38.710
I multiply the heat of
vaporization, which is 2,257

00:11:38.710 --> 00:11:43.730
joules per gram times
200 grams. And

00:11:43.730 --> 00:11:57.865
this is equal to 451,400.

00:11:57.865 --> 00:11:59.970
I'll do it in that blue color.

00:11:59.970 --> 00:12:06.560
451,400 joules.

00:12:06.560 --> 00:12:14.850
So this piece right here is
451,000 for our sample of 200

00:12:14.850 --> 00:12:20.650
grams. This piece right here
was 83,000 joules.

00:12:20.650 --> 00:12:25.580
This piece right here
was 3,780 joules.

00:12:25.580 --> 00:12:28.470
So to know the total amount of
energy, the total amount of

00:12:28.470 --> 00:12:31.580
heat that we had to put in the
system to go from minus 10

00:12:31.580 --> 00:12:37.890
degree ice all the way to 110
degree vapor, we just add up

00:12:37.890 --> 00:12:41.170
all of the energies we had to
do in all of these steps.

00:12:41.170 --> 00:12:41.800
Let's see.

00:12:41.800 --> 00:12:44.280
And I'll do them in
order this time.

00:12:44.280 --> 00:12:53.080
So to go from minus 10 degree
ice to zero degree ice.

00:12:53.080 --> 00:12:54.860
Of course we have
200 grams of it.

00:12:54.860 --> 00:12:58.940
It was 4,100.

00:12:58.940 --> 00:13:05.530
Plus the 67,000.

00:13:05.530 --> 00:13:06.850
I'm just doing this
off the screen.

00:13:06.850 --> 00:13:12.710
So plus 67,110.

00:13:12.710 --> 00:13:15.780
Plus 83,000.

00:13:15.780 --> 00:13:19.450
That's to go from zero degree
water to 100 degree water.

00:13:19.450 --> 00:13:24.210
Plus 83,560.

00:13:24.210 --> 00:13:27.360
So we're at 154,000 right
now just to get

00:13:27.360 --> 00:13:29.130
to 100 degree water.

00:13:29.130 --> 00:13:31.950
And then we need to turn that
100 degree water into 100

00:13:31.950 --> 00:13:33.090
degree vapor.

00:13:33.090 --> 00:13:35.280
So you add the 451,000.

00:13:35.280 --> 00:13:41.330
So, plus 451,400 is
equal to 606.

00:13:41.330 --> 00:13:44.840
And then finally, we're at 100
degree vapor, and we want to

00:13:44.840 --> 00:13:47.360
convert that to 110
degree vapor.

00:13:47.360 --> 00:13:50.030
So it's another 3,700 joules.

00:13:50.030 --> 00:14:00.430
So plus 3,780 is equal
to 609,950 joules.

00:14:00.430 --> 00:14:03.840
So this whole thing when we're
dealing with 200 grams, when

00:14:03.840 --> 00:14:07.400
you're going from
minus 10 to 110.

00:14:07.400 --> 00:14:09.910
And remember, this is
for 200 grams. It

00:14:09.910 --> 00:14:16.070
took us 609,950 joules.

00:14:16.070 --> 00:14:20.650
Or 609 kilojoules to do this.

00:14:20.650 --> 00:14:22.470
So that by itself is an
interesting thing.

00:14:22.470 --> 00:14:24.340
You might think, wow, this
is a huge number.

00:14:24.340 --> 00:14:26.830
But actually, it turns out
joules isn't a lot of work.

00:14:26.830 --> 00:14:29.580
Kilojoules starts to become
a little bit interesting.

00:14:29.580 --> 00:14:33.570
You might realize, 200 grams
of ice, that's about half a

00:14:33.570 --> 00:14:34.410
pound of ice.

00:14:34.410 --> 00:14:37.650
So to take half a pound of ice
and warm it up on your stove

00:14:37.650 --> 00:14:43.600
would take 609 kilojoules
of heat to do that.

00:14:43.600 --> 00:14:45.890
So that's something that you
probably could do on your

00:14:45.890 --> 00:14:48.010
stove at home.


States of matter follow-up

WEBVTT
Kind: captions
Language: en

00:00:00.560 --> 00:00:03.580
In the last video we touched on
the three states of matter

00:00:03.580 --> 00:00:06.990
that are really most familiar
to our everyday experience.

00:00:06.990 --> 00:00:12.410
The solid, the liquid,
and the gas.

00:00:12.410 --> 00:00:14.910
And I kind of hinted that there
is a fourth state, which

00:00:14.910 --> 00:00:17.310
I don't cover, because it's
usually not the domain of an

00:00:17.310 --> 00:00:18.560
introductory chemistry course.

00:00:18.560 --> 00:00:20.750
But a little bit of a discussion
ensued on the

00:00:20.750 --> 00:00:22.340
message board for that video.

00:00:22.340 --> 00:00:24.910
So I thought I would at least
touch on that fourth stage.

00:00:24.910 --> 00:00:26.580
And that's plasma.

00:00:26.580 --> 00:00:30.970
I'll do it in a suitably
bright color.

00:00:30.970 --> 00:00:32.040
Plasma.

00:00:32.040 --> 00:00:34.110
And people consider it a fourth
state because it has

00:00:34.110 --> 00:00:36.480
some properties of gases.

00:00:36.480 --> 00:00:39.430
In some ways it's almost
a subset of gases.

00:00:39.430 --> 00:00:42.880
But it also has properties of
conductivity that you normally

00:00:42.880 --> 00:00:46.350
wouldn't associate with a gas.

00:00:46.350 --> 00:00:50.100
And just so you know, when you
first hear it you think, oh

00:00:50.100 --> 00:00:52.990
that's a fairly exotic
thing, plasma.

00:00:52.990 --> 00:00:55.450
And in the first video, I said
it's only something that

00:00:55.450 --> 00:00:56.690
occurs at high temperatures,
which isn't

00:00:56.690 --> 00:00:58.370
exactly 100% right.

00:00:58.370 --> 00:01:00.120
It doesn't have to be at
high temperatures.

00:01:00.120 --> 00:01:02.730
I really should have said
that under extenuating

00:01:02.730 --> 00:01:04.670
circumstances where you
have a very strong

00:01:04.670 --> 00:01:06.040
electromagnetic field.

00:01:06.040 --> 00:01:10.550
Or something has to happen to
essentially bump the the

00:01:10.550 --> 00:01:14.580
electrons, or move the electrons
off of gases that

00:01:14.580 --> 00:01:16.410
would've otherwise have
kept their electrons.

00:01:16.410 --> 00:01:18.540
So it's kind of analogous to
what happens in metal.

00:01:18.540 --> 00:01:21.170
When we talk about metal bonds,
we talk about this

00:01:21.170 --> 00:01:23.470
notion of a sea of electrons.

00:01:23.470 --> 00:01:26.150
Let's say if we talked
about iron.

00:01:26.150 --> 00:01:30.130
What happens with most metals
is that they have so many

00:01:30.130 --> 00:01:33.220
electrons, and they are so
willing to give them, that the

00:01:33.220 --> 00:01:37.990
electrons just kind of float
outside of the atoms

00:01:37.990 --> 00:01:41.250
themselves and create this kind
of big sea of electrons.

00:01:41.250 --> 00:01:43.760
And then the atoms
themselves become

00:01:43.760 --> 00:01:47.110
positively charged ions.

00:01:47.110 --> 00:01:49.020
Because they essentially
donated some

00:01:49.020 --> 00:01:49.870
electrons to the sea.

00:01:49.870 --> 00:01:52.220
So they're attracted to the sea
and that's what makes them

00:01:52.220 --> 00:01:54.480
malleable and even more
importantly what allows them

00:01:54.480 --> 00:01:55.510
to conduct electricity.

00:01:55.510 --> 00:01:58.300
But they're all really packed
closely together and it's a

00:01:58.300 --> 00:01:59.710
very dense structure.

00:01:59.710 --> 00:02:03.320
Plasma is a situation where if
you take gases, and remember,

00:02:03.320 --> 00:02:05.640
in gases things are
pretty far apart.

00:02:05.640 --> 00:02:07.700
So you take a bunch of
gases and they have

00:02:07.700 --> 00:02:08.699
high kinetic energy.

00:02:08.699 --> 00:02:12.340
Although, they don't have to be,
that could be under very

00:02:12.340 --> 00:02:12.970
low pressure.

00:02:12.970 --> 00:02:14.950
But they're moving around and
bumping into each other.

00:02:14.950 --> 00:02:16.740
But they're not close
to each other.

00:02:16.740 --> 00:02:19.450
They don't have a fixed
structure with each other.

00:02:19.450 --> 00:02:21.140
Or they're not rubbing against
each other like in

00:02:21.140 --> 00:02:22.430
the case of a liquid.

00:02:22.430 --> 00:02:26.160
But what happens in a plasma, or
one situation is, that you

00:02:26.160 --> 00:02:29.770
apply such a strong
electromagnetic field that the

00:02:29.770 --> 00:02:32.460
electrons want to
disassociate.

00:02:32.460 --> 00:02:34.130
So let's say these
electrons start

00:02:34.130 --> 00:02:37.220
bumping off of the plasma.

00:02:37.220 --> 00:02:40.530
And so a solid has
its own shape.

00:02:40.530 --> 00:02:43.300
A plasma will take the shape of
its container like a gas.

00:02:43.300 --> 00:02:46.350
And sometimes it is described
as an ionized gas.

00:02:46.350 --> 00:02:47.810
And it's described as
ionized because

00:02:47.810 --> 00:02:49.850
electrons are bumped off.

00:02:49.850 --> 00:02:52.320
And when the electrons are
bumped off, the otherwise

00:02:52.320 --> 00:02:57.310
neutral atoms now have
positive charges.

00:02:57.310 --> 00:02:59.830
And what this allows is,
essentially a conduction of

00:02:59.830 --> 00:03:00.450
electricity.

00:03:00.450 --> 00:03:02.960
Because now these electrons
are free to move.

00:03:02.960 --> 00:03:06.460
You might say that sounds like
a bizarre state of matter,

00:03:06.460 --> 00:03:07.550
where does it exist?

00:03:07.550 --> 00:03:10.930
Well, probably closest to home,
it exists in lightning.

00:03:13.940 --> 00:03:16.580
And that's worthy of
an entire video.

00:03:16.580 --> 00:03:19.300
But the idea is that you start
having a huge potential

00:03:19.300 --> 00:03:22.765
difference between the clouds
and the ground.

00:03:26.150 --> 00:03:28.480
And then because you have this
huge voltage difference

00:03:28.480 --> 00:03:31.710
between the two, you have
electrons that are essentially

00:03:31.710 --> 00:03:35.090
wanting to go into the ground.

00:03:35.090 --> 00:03:42.400
You have a build-up of electrons
up here that want to

00:03:42.400 --> 00:03:44.270
go into the ground.

00:03:44.270 --> 00:03:46.870
They can't because
air is normally

00:03:46.870 --> 00:03:50.390
a fairly bad conductor.

00:03:50.390 --> 00:03:51.250
It's an insulator.

00:03:51.250 --> 00:03:53.490
But what happens is because
there's so much

00:03:53.490 --> 00:03:56.540
electropotential here, the
electrons that are close in

00:03:56.540 --> 00:04:01.100
the molecules up here, at least
how I visualize it,

00:04:01.100 --> 00:04:04.890
their electrons want to escape
from these clouds.

00:04:04.890 --> 00:04:06.980
So their electrons start
to want to move

00:04:06.980 --> 00:04:09.300
away in the air molecules.

00:04:09.300 --> 00:04:11.130
Whether you're talking about
the air is a mixture of

00:04:11.130 --> 00:04:13.750
oxygen, and nitrogen,
and carbon dioxide.

00:04:13.750 --> 00:04:15.780
They start wanting to get
away from the clouds.

00:04:15.780 --> 00:04:19.079
So they start disassociating
and start forming

00:04:19.079 --> 00:04:20.950
this ionized air.

00:04:20.950 --> 00:04:24.520
And eventually, at some point,
this happens to such a degree

00:04:24.520 --> 00:04:28.210
that you can actually get
conduction from the cloud to

00:04:28.210 --> 00:04:29.610
the ground.

00:04:29.610 --> 00:04:35.850
And that conduction is when the
air is in a plasma state.

00:04:35.850 --> 00:04:38.550
The conduction allows extremely
high temperatures

00:04:38.550 --> 00:04:41.620
and the electrons to flow all
the way to the ground.

00:04:41.620 --> 00:04:44.750
The other common example, you
might see something like this,

00:04:44.750 --> 00:04:47.410
well actually not like this, but
at least a plasma state,

00:04:47.410 --> 00:04:48.360
is in stars.

00:04:48.360 --> 00:04:50.390
And that's because you
have extremely strong

00:04:50.390 --> 00:04:54.400
electromagnetic fields,
extremely high pressure, and

00:04:54.400 --> 00:04:58.480
in that type of environment,
once again, I'm old super over

00:04:58.480 --> 00:05:00.870
simplifying it, you can get to
a state where the electrons

00:05:00.870 --> 00:05:04.580
can get disassociated from
things that otherwise wouldn't

00:05:04.580 --> 00:05:05.620
want to give up their
electrons.

00:05:05.620 --> 00:05:07.410
I thought I would touch on
that because it's an

00:05:07.410 --> 00:05:08.470
interesting subject.

00:05:08.470 --> 00:05:11.820
And it exists in the universe.

00:05:11.820 --> 00:05:14.760
On the universal level, because
stars are pretty much

00:05:14.760 --> 00:05:18.295
all plasma, it is actually the
most common state of matter in

00:05:18.295 --> 00:05:19.000
the universe.

00:05:19.000 --> 00:05:22.410
Although in our everyday life,
we probably encounter solids,

00:05:22.410 --> 00:05:24.420
liquids and gases a lot more.

00:05:24.420 --> 00:05:27.590
And one other thing I want to
maybe clarify from the last

00:05:27.590 --> 00:05:29.300
video is, I talk about
the bonding

00:05:29.300 --> 00:05:32.350
between water molecules.

00:05:32.350 --> 00:05:34.180
And let's say we're talking
in the solid state.

00:05:34.180 --> 00:05:38.660
So I have an oxygen, a
hydrogen, a hydrogen.

00:05:38.660 --> 00:05:41.720
And I have some electrons here,
some electrons here.

00:05:41.720 --> 00:05:46.866
Let's say there's another
hydrogen here, an oxygen, and

00:05:46.866 --> 00:05:48.070
a hydrogen.

00:05:48.070 --> 00:05:50.840
Maybe there's an oxygen here.

00:05:50.840 --> 00:05:52.125
That has hydrogen.

00:05:58.710 --> 00:06:00.130
And then this has a hydrogen.

00:06:00.130 --> 00:06:03.370
And it has two electrons,
two electron pairs.

00:06:03.370 --> 00:06:07.140
So I talked about the notion,
and we talked about it many

00:06:07.140 --> 00:06:07.620
times before.

00:06:07.620 --> 00:06:10.140
That oxygen is so much more
electronegative that it hogs

00:06:10.140 --> 00:06:11.350
the electrons.

00:06:11.350 --> 00:06:13.100
And so the oxygen side
starts to have a

00:06:13.100 --> 00:06:15.060
partial negative charge.

00:06:15.060 --> 00:06:16.900
While the hydrogen side
starts to have a

00:06:16.900 --> 00:06:17.950
partial positive side.

00:06:17.950 --> 00:06:19.420
Because with the hydrogen,
essentially all of its

00:06:19.420 --> 00:06:23.730
electrons are hanging out close
to the oxygen, hydrogen

00:06:23.730 --> 00:06:25.590
ends up just becoming like
this proton that's

00:06:25.590 --> 00:06:26.130
floating out there.

00:06:26.130 --> 00:06:27.310
Because we said it
doesn't even have

00:06:27.310 --> 00:06:29.180
neutrons in most cases.

00:06:29.180 --> 00:06:30.620
So this has a slightly
positive charge.

00:06:30.620 --> 00:06:32.400
This one has a positive
charge.

00:06:32.400 --> 00:06:38.560
And the positive polar end
of the water molecule is

00:06:38.560 --> 00:06:40.290
attracted to the negative
polar end.

00:06:40.290 --> 00:06:45.730
And I called it polar bonds,
and it shows you my memory

00:06:45.730 --> 00:06:48.745
from high school chemistry is
not ideal, I really should

00:06:48.745 --> 00:06:52.280
have called it hydrogen bonds.

00:06:52.280 --> 00:06:56.010
So this is a hydrogen bond, and
this is a hydrogen bond.

00:06:56.010 --> 00:06:58.810
It's just a matter of
the name I used.

00:06:58.810 --> 00:07:00.780
I just want to clarify that
because that is what's

00:07:00.780 --> 00:07:02.480
typically used in your
chemistry class.

00:07:02.480 --> 00:07:03.620
I don't want to confuse you.

00:07:03.620 --> 00:07:08.680
And that is just the bond that
exists from a partially

00:07:08.680 --> 00:07:10.530
positive hydrogen atom.

00:07:10.530 --> 00:07:14.400
Because its electrons are
hanging out near the oxygen.

00:07:14.400 --> 00:07:18.980
And a partially negative
oxygen atom

00:07:18.980 --> 00:07:20.200
in the water molecule.

00:07:20.200 --> 00:07:22.920
Because it has stolen
all of these

00:07:22.920 --> 00:07:24.580
electrons from the hydrogen.

00:07:24.580 --> 00:07:26.680
You draw it like that, it's
called a hydrogen bond.

00:07:26.680 --> 00:07:31.960
And hydrogen bonds tend to
form between hydrogen or

00:07:31.960 --> 00:07:35.740
really only a handful of super
electronegative atoms. And

00:07:35.740 --> 00:07:40.500
that's nitrogen, fluorine,
and oxygen.

00:07:40.500 --> 00:07:44.230
And these are actually the three
most electronegative

00:07:44.230 --> 00:07:54.680
atoms. So the nitrogen, NH3,
when it bonds with hydrogen,

00:07:54.680 --> 00:07:56.940
is essentially so
electronegative that you have

00:07:56.940 --> 00:07:58.210
the same situation.

00:07:58.210 --> 00:08:00.410
All the electrons hang out here,
so you have a partial

00:08:00.410 --> 00:08:04.770
negative charge, partial
positive on the hydrogen ends.

00:08:04.770 --> 00:08:08.840
Same thing with hydrogen
fluorine.

00:08:08.840 --> 00:08:11.410
You get the same HF.

00:08:11.410 --> 00:08:13.740
You get the same type
of hydrogen bonds.

00:08:13.740 --> 00:08:17.280
And so in this case, these guys
would be attracted to the

00:08:17.280 --> 00:08:19.190
nitrogen part of other molecules
and would form

00:08:19.190 --> 00:08:19.820
hydrogen bonds.

00:08:19.820 --> 00:08:21.340
I just want to get that
out of the way.

00:08:21.340 --> 00:08:23.720
And with that done, I think we
can return to some of the

00:08:23.720 --> 00:08:31.200
ideas of the last video and
actually do some problems.

00:08:31.200 --> 00:08:32.450
Let's take the case
with water.

00:08:36.950 --> 00:08:39.780
Actually, let me just state the
problem first. So let's

00:08:39.780 --> 00:08:43.600
say that we have a