Capillary action and why we see a meniscus

WEBVTT
Kind: captions
Language: en

00:00:00.334 --> 00:00:02.213
- If you were to take a glass beaker,

00:00:02.303 --> 00:00:03.593
so let me draw it right over here.

00:00:03.963 --> 00:00:05.463
If you were to take a glass beaker

00:00:05.643 --> 00:00:07.963
and you were to fill it up with water,

00:00:08.323 --> 00:00:09.814
you might expect that the surface

00:00:09.814 --> 00:00:11.714
of the water would be flat.

00:00:12.294 --> 00:00:13.775
But it's actually not the case

00:00:13.775 --> 00:00:14.824
and I encourage you to try it.

00:00:14.824 --> 00:00:16.323
You might have even observed this before.

00:00:16.483 --> 00:00:18.264
The surface of the water will not be flat.

00:00:18.264 --> 00:00:21.053
The surface of the water
will actually be higher

00:00:21.053 --> 00:00:24.463
near the glass than it is
when it's away from the glass.

00:00:24.603 --> 00:00:28.571
It forms a shape that
looks something like that.

00:00:29.072 --> 00:00:30.212
And so the first thing we might ask

00:00:30.212 --> 00:00:31.812
is what'll we call this thing.

00:00:31.812 --> 00:00:33.992
And this right over here
is called a meniscus.

00:00:34.562 --> 00:00:35.661
Meniscus.

00:00:36.311 --> 00:00:38.002
And in particular this meniscus,

00:00:38.002 --> 00:00:40.402
because the fluid is
higher near the container

00:00:40.402 --> 00:00:42.552
than it is when you're
away from the container,

00:00:42.552 --> 00:00:47.152
we would call this a
concave, concave meniscus.

00:00:47.482 --> 00:00:49.672
And you might say, "Well if
this is a concave meniscus,

00:00:49.672 --> 00:00:51.902
"are there any situations where might have

00:00:51.902 --> 00:00:54.422
"a convex meniscus?"

00:00:54.951 --> 00:00:57.203
Well sure, you can have a convex meniscus.

00:00:57.653 --> 00:01:00.261
If you were take that same glass beaker,

00:01:00.741 --> 00:01:01.862
instead of filling it with water

00:01:01.862 --> 00:01:03.641
if you filled it with say, mercury.

00:01:04.181 --> 00:01:05.442
If you filled it with mercury,

00:01:05.742 --> 00:01:08.142
you would get a meniscus
that looks like this

00:01:08.142 --> 00:01:09.852
where there's a bulge near the center

00:01:09.852 --> 00:01:11.372
when you're further
away from the container

00:01:11.372 --> 00:01:12.753
than when you're at the container.

00:01:13.142 --> 00:01:15.476
And so let me just label this.

00:01:15.476 --> 00:01:19.465
This is a convex, convex meniscus.

00:01:20.036 --> 00:01:23.466
But it's one thing to just
observe this and to name them.

00:01:23.466 --> 00:01:24.976
To say, "Hey this is a meniscus."

00:01:24.976 --> 00:01:26.355
So this is a concave meniscus.

00:01:26.515 --> 00:01:28.136
But a more interesting question is

00:01:28.136 --> 00:01:30.025
why does it actually happen.

00:01:30.565 --> 00:01:33.896
And so you might imagine
this concave meniscus

00:01:34.086 --> 00:01:36.416
is because the fluid is more attracted

00:01:36.416 --> 00:01:39.226
to the container than it is to itself.

00:01:39.626 --> 00:01:40.486
And you might be saying, "Wait, wait.

00:01:40.486 --> 00:01:41.986
"Hold on, hold on a second here.

00:01:41.986 --> 00:01:44.365
"We've been talking about how water

00:01:44.365 --> 00:01:47.696
"has this polarity, it
has partial negative end.

00:01:47.696 --> 00:01:50.535
"Each water molecule
has a partially negative

00:01:50.835 --> 00:01:53.135
"and has partially positive
ends at the hydrogens."

00:01:53.655 --> 00:01:54.596
So let me write this down.

00:01:54.596 --> 00:01:59.565
Partial positive charges at the hydrogens.

00:01:59.795 --> 00:02:02.245
And that causes this
hydrogen bonding to form

00:02:02.245 --> 00:02:04.366
and that's what kind of gives water

00:02:04.366 --> 00:02:05.846
all of these special properties.

00:02:05.846 --> 00:02:07.365
"You're telling me that
it's more attracted

00:02:07.365 --> 00:02:09.266
to the glass than it is to itself?"

00:02:09.586 --> 00:02:11.627
And I would say, "Yes,
I am telling you that."

00:02:11.717 --> 00:02:13.455
And you could imagine
why it is going to be

00:02:13.455 --> 00:02:15.335
more attracted to the glass than itself,

00:02:15.595 --> 00:02:17.396
because glass actually has,

00:02:17.396 --> 00:02:21.466
the molecules in glass
actually are quite polar.

00:02:22.066 --> 00:02:26.966
Glass, typically made up
of silicon oxide lattice.

00:02:27.186 --> 00:02:30.645
For every one silicon atom,
you have two oxygen atoms.

00:02:30.645 --> 00:02:31.836
You see that right over here.

00:02:31.836 --> 00:02:35.105
For every one silicon,
you have two oxygen atoms.

00:02:35.257 --> 00:02:39.466
And it turns out that the
electronegativity difference

00:02:39.466 --> 00:02:42.255
between oxygen and silicon is even higher

00:02:42.255 --> 00:02:44.036
than the electronegativity difference

00:02:44.196 --> 00:02:46.386
between oxygen and hydrogen.

00:02:46.386 --> 00:02:49.176
Silicon is even less
electronegative than hydrogen.

00:02:49.446 --> 00:02:54.116
So the oxygens are really able
to hog silicon's electrons.

00:02:54.116 --> 00:02:57.516
Especially the ones that
are involved in the bonding.

00:02:57.816 --> 00:03:00.486
So you have partial charges,
partial positive charges

00:03:00.486 --> 00:03:02.715
form at the silicon
and then you still have

00:03:02.715 --> 00:03:06.827
partial negative charges
form around the oxygens.

00:03:07.147 --> 00:03:08.837
Form around the oxygens.

00:03:09.046 --> 00:03:10.106
So these are partial negative.

00:03:10.106 --> 00:03:11.797
And partial positive at the silicon.

00:03:12.137 --> 00:03:13.246
And so you could imagine what's going

00:03:13.246 --> 00:03:14.166
to happen at the interface.

00:03:14.166 --> 00:03:16.025
And let me make this
clear what's going on.

00:03:16.145 --> 00:03:20.776
This, what I am circling
right now, that is the water.

00:03:21.306 --> 00:03:23.956
This right over here,
that's the water molecules.

00:03:24.586 --> 00:03:26.606
And what we see over here,

00:03:27.176 --> 00:03:30.482
what we see over here, these
are the glass molecules.

00:03:30.482 --> 00:03:32.792
So this is the glass right over here.

00:03:33.292 --> 00:03:35.342
And sure the water is attracted to itself

00:03:36.202 --> 00:03:37.623
because of the hydrogen bonds.

00:03:37.623 --> 00:03:39.343
But it has some kinetic energy,

00:03:39.343 --> 00:03:41.042
remember these things are jostling around,

00:03:41.042 --> 00:03:43.313
they're bouncing around,
we're in a liquid state.

00:03:43.653 --> 00:03:44.913
And so you can imagine all of a sudden,

00:03:44.913 --> 00:03:48.647
maybe this, let me see,
maybe this character,

00:03:48.647 --> 00:03:50.258
this water molecule right over here.

00:03:50.558 --> 00:03:52.559
Maybe a moment ago it was right over here

00:03:52.559 --> 00:03:53.618
but it popped up here.

00:03:53.618 --> 00:03:55.169
It just got knocked by another molecule,

00:03:55.169 --> 00:03:56.798
it had enough kinetic
energy to jump up here.

00:03:56.938 --> 00:03:59.019
But once it came up, came in contact

00:03:59.019 --> 00:04:03.129
with the glass surface right
over here, the glass molecules.

00:04:03.129 --> 00:04:04.348
It stuck to them.

00:04:04.538 --> 00:04:07.518
Because its partially positive end,

00:04:07.838 --> 00:04:10.149
its partially positive
end at the hydrogens.

00:04:10.469 --> 00:04:12.358
Let me do it in that green color.

00:04:12.668 --> 00:04:15.229
The partially positive
end at the hydrogens

00:04:15.509 --> 00:04:17.709
would be attracted to the
partially negative ends

00:04:17.709 --> 00:04:20.559
of the oxygens in the glass.

00:04:20.629 --> 00:04:21.958
And so it'll stick to it.

00:04:21.958 --> 00:04:23.989
This is actually a stronger partial charge

00:04:23.989 --> 00:04:26.199
than what you would
actually see in the water

00:04:26.199 --> 00:04:28.449
because there's a bigger
electronegativity difference

00:04:28.449 --> 00:04:30.538
between the silicon and
the oxygen in the glass

00:04:30.848 --> 00:04:33.529
than the oxygen and the
hydrogen in the water.

00:04:33.709 --> 00:04:35.509
So these things just keep bumping around.

00:04:35.509 --> 00:04:36.758
Maybe there's another water molecule

00:04:36.758 --> 00:04:38.088
that just get knocked in the right way.

00:04:38.088 --> 00:04:39.378
All of a sudden for, you know,

00:04:39.378 --> 00:04:41.429
a very brief moment it
gets knocked up here.

00:04:41.689 --> 00:04:44.499
And then it's going to stick to the glass.

00:04:44.789 --> 00:04:47.088
And this phenomenon of something sticking

00:04:47.088 --> 00:04:50.110
to its container, we
would call that adhesion.

00:04:50.500 --> 00:04:52.219
So what you see going on here,

00:04:52.409 --> 00:04:56.689
that is called adhesion, adhesion.

00:04:56.689 --> 00:04:59.679
And adhesion is the
reason why you also see

00:04:59.839 --> 00:05:01.298
the water a little bit higher there.

00:05:01.668 --> 00:05:04.179
When you talk about
something sticking to itself,

00:05:04.319 --> 00:05:05.509
we call that cohesion.

00:05:05.509 --> 00:05:06.619
And that's what the hydrogen bonds

00:05:06.619 --> 00:05:07.778
are doing inside the water.

00:05:08.108 --> 00:05:10.739
So this right over here, that over there,

00:05:11.049 --> 00:05:14.809
that is co-, that is cohesion.

00:05:15.199 --> 00:05:17.289
So that's why we have things,

00:05:17.289 --> 00:05:19.299
why we observe a meniscus like this.

00:05:19.639 --> 00:05:23.199
But there's even more fascinating
properties of adhesion.

00:05:23.529 --> 00:05:27.309
If I were to take, if I were
to take a container of water.

00:05:28.259 --> 00:05:29.909
If I were to take a container of water.

00:05:29.909 --> 00:05:31.639
And just to be clear what's
going on here with the mercury,

00:05:31.639 --> 00:05:33.579
the mercury is more attracted to itself

00:05:33.579 --> 00:05:35.130
than it is to the glass container,

00:05:35.130 --> 00:05:36.589
so it bulges right over there.

00:05:36.839 --> 00:05:37.979
But let's go back to water.

00:05:37.979 --> 00:05:39.990
So let's say that this
is a big tub of water.

00:05:40.340 --> 00:05:41.208
I fill it.

00:05:41.658 --> 00:05:45.569
So, I fill the water right over here.

00:05:45.939 --> 00:05:47.729
And let's say I take a glass tube,

00:05:47.729 --> 00:05:49.069
and the material matters.

00:05:49.069 --> 00:05:50.869
It has to be a polar material.

00:05:50.869 --> 00:05:52.989
That's why you'll see
the meniscus in glass,

00:05:52.989 --> 00:05:54.839
but you might not see
it or you won't see it

00:05:54.839 --> 00:05:56.329
if you were dealing with a plastic tube

00:05:56.329 --> 00:05:59.058
because the plastic does
not have that polarity.

00:05:59.398 --> 00:06:00.908
But let's say you were
to take a glass tube,

00:06:01.258 --> 00:06:02.960
a thin glass tube this time.

00:06:03.280 --> 00:06:04.909
So much thinner than even a beaker.

00:06:04.909 --> 00:06:08.060
So you take a thin glass tube
and you stick it in the water,

00:06:08.060 --> 00:06:09.850
you will observe something very cool.

00:06:09.850 --> 00:06:10.749
And I encourage you to do this

00:06:10.749 --> 00:06:12.689
if you can get your hands
on a very thin glass tube.

00:06:12.999 --> 00:06:14.949
You will notice that the
water is actually going to

00:06:14.949 --> 00:06:19.359
defy gravity and start climbing
up this thin glass tube.

00:06:19.729 --> 00:06:21.709
And so that's interesting.

00:06:21.709 --> 00:06:22.749
Why is that happening?

00:06:23.269 --> 00:06:26.249
Well this phenomenon which
we call capillary action.

00:06:26.809 --> 00:06:29.329
Capillary, capillary action.

00:06:29.329 --> 00:06:31.869
The word capillary, it'll
refer to anything from

00:06:31.869 --> 00:06:34.119
you know, a very, very narrow tube

00:06:34.119 --> 00:06:36.529
and we also have capillaries
in our circulation system.

00:06:36.529 --> 00:06:38.509
Capillaries are our
thinnest blood vessels,

00:06:38.509 --> 00:06:40.119
those are very, very, very, very thin.

00:06:40.119 --> 00:06:41.581
And there's actually capillary action

00:06:41.581 --> 00:06:43.329
inside of our capillaries.

00:06:43.529 --> 00:06:44.450
But what we're seeing here,

00:06:44.450 --> 00:06:47.509
this is called capillary,
capillary action.

00:06:47.859 --> 00:06:51.830
And it's really just this
adhesion occurring more intensely

00:06:51.830 --> 00:06:54.780
because more of the water
molecules are able to come

00:06:54.780 --> 00:06:58.149
in touch with the polar glass lattice.

00:06:58.439 --> 00:07:00.499
And so you can imagine we have glass here.

00:07:00.649 --> 00:07:03.739
If you also had glass over here.

00:07:03.739 --> 00:07:05.169
And actually it would be very hard to find

00:07:05.169 --> 00:07:06.779
something that thin that's on the order

00:07:06.779 --> 00:07:07.861
of only a few molecules.

00:07:07.861 --> 00:07:09.629
But this is, I'm not
drawing things in scale.

00:07:09.769 --> 00:07:10.851
You can imagine now okay,

00:07:10.851 --> 00:07:12.659
maybe another water
molecule could jump up here

00:07:12.659 --> 00:07:13.639
and stick to the glass there.

00:07:13.639 --> 00:07:15.310
And one just gets bumped the right way,

00:07:15.500 --> 00:07:16.970
jumps up and jump there.

00:07:16.970 --> 00:07:19.340
And if we didn't have a polar container,

00:07:19.340 --> 00:07:21.490
if we didn't have a hydrophilic container,

00:07:21.890 --> 00:07:24.220
well then the thing might
just jump back down.

00:07:24.220 --> 00:07:26.760
But because it went up there,
it kind of just stuck to it.

00:07:26.760 --> 00:07:28.419
And then it's vibrating there

00:07:28.419 --> 00:07:30.409
and then maybe another water
molecule gets attracted to it

00:07:30.409 --> 00:07:31.509
because of its hydrogen bonds.

00:07:31.509 --> 00:07:33.120
Then it gets bumped the right way.

00:07:33.300 --> 00:07:35.230
And then it gets bumped with the higher

00:07:35.230 --> 00:07:36.600
part of the container
but then it sticks there.

00:07:36.600 --> 00:07:38.899
And so it starts climbing the container.

00:07:39.369 --> 00:07:40.799
And that's what capillary action is

00:07:40.799 --> 00:07:43.000
and it's not just some neat parlor trick,

00:07:43.220 --> 00:07:45.591
we actually probably use capillary action

00:07:45.591 --> 00:07:47.259
in our every day lives all the time.

00:07:47.259 --> 00:07:48.929
Beyond the fact that
it's actually happening

00:07:48.929 --> 00:07:51.520
in your capillaries in your
body that allows you to live,

00:07:51.810 --> 00:07:54.930
but if you have a, if you spill
something on your counter.

00:07:54.930 --> 00:07:57.100
So let's say that's a
spill right over there.

00:07:57.100 --> 00:07:58.619
You spill some maybe,
you spill some water,

00:07:58.619 --> 00:08:00.099
or you spill some milk.

00:08:00.289 --> 00:08:01.759
And if you take a paper towel.

00:08:02.169 --> 00:08:03.669
If you take a paper towel.

00:08:03.669 --> 00:08:05.609
In fact, if you took a
paper towel like this.

00:08:05.609 --> 00:08:09.528
If you held it vertically,
you will see the water

00:08:09.528 --> 00:08:12.230
start to be absorbed into the paper towel.

00:08:13.480 --> 00:08:15.849
This kind of absorption
action that you see,

00:08:15.849 --> 00:08:18.039
that actually is capillary action.

00:08:18.219 --> 00:08:20.249
It's the water going into
the small little gaps

00:08:20.249 --> 00:08:23.108
of the paper towel, but
that's because it is attracted

00:08:23.108 --> 00:08:25.080
to the actual paper towel.


Surface tension

WEBVTT
Kind: captions
Language: en

00:00:00.250 --> 00:00:02.607
- What we have here is a zoom-in

00:00:02.607 --> 00:00:04.820
of the surface of water.

00:00:04.820 --> 00:00:08.120
So up here you have the
air, this is the air,

00:00:08.120 --> 00:00:09.350
these are some air molecules,

00:00:09.350 --> 00:00:10.790
maybe they're nitrogen molecules.

00:00:10.790 --> 00:00:12.310
They're fairly far apart,
in fact, in reality,

00:00:12.310 --> 00:00:14.720
they would be even more
far apart than this.

00:00:14.720 --> 00:00:16.920
And then over here you
have water molecules.

00:00:16.920 --> 00:00:18.050
We've seen this many times.

00:00:18.050 --> 00:00:20.250
You have the oxygen atom and it's bonded

00:00:20.250 --> 00:00:22.950
to two hydrogen atoms, and the oxygen atom

00:00:22.950 --> 00:00:24.510
likes to hog the electrons more.

00:00:24.510 --> 00:00:25.820
It's more electronegative, so you have

00:00:25.820 --> 00:00:27.650
a partially negative charge at this end

00:00:27.650 --> 00:00:29.590
and partially positive ends at this end.

00:00:29.590 --> 00:00:31.050
And that attraction between the

00:00:31.050 --> 00:00:33.420
partially positive ends and
the partially negative ends,

00:00:33.420 --> 00:00:36.490
that's what gives water all
sorts of neat properties.

00:00:36.490 --> 00:00:38.490
Those are the hydrogen bonds.

00:00:38.490 --> 00:00:41.090
Those are the hydrogen
bonds that give water

00:00:41.090 --> 00:00:43.720
all sorts of neat properties and keep it

00:00:43.720 --> 00:00:45.550
in its liquid state at a standard

00:00:45.550 --> 00:00:47.550
temperature and pressure.

00:00:47.550 --> 00:00:48.723
Now what I want to think about

00:00:48.723 --> 00:00:51.090
is the surface in particular.

00:00:51.090 --> 00:00:52.780
And if you look at the surface of water,

00:00:52.780 --> 00:00:54.250
it might look completely smooth.

00:00:54.250 --> 00:00:55.920
But if you were to zoom
in on a molecular level,

00:00:55.920 --> 00:00:58.200
you'll see that, well, it's
just made up of these molecules.

00:00:58.200 --> 00:01:00.490
But roughly speaking, roughly speaking,

00:01:00.490 --> 00:01:02.020
let's just say that this is roughly

00:01:02.020 --> 00:01:05.593
the surface, the surface of the water.

00:01:05.593 --> 00:01:07.950
The surface of the water.

00:01:07.950 --> 00:01:09.620
Now, what's going on at the surface?

00:01:09.620 --> 00:01:10.690
Well, all these molecules

00:01:10.690 --> 00:01:12.590
are interacting through hydrogen bonds.

00:01:12.590 --> 00:01:14.190
Let's say this molecule right over here,

00:01:14.190 --> 00:01:17.510
it has hydrogen bonds
pulling on it upwards,

00:01:17.510 --> 00:01:19.390
up to this one, pulling it this way,

00:01:19.390 --> 00:01:21.420
pulling it downwards,
pulling it in really,

00:01:21.420 --> 00:01:25.620
really, to some degree,
almost every direction.

00:01:25.620 --> 00:01:27.190
And they all have their kinetic energy

00:01:27.190 --> 00:01:28.320
and they're bumping around, but they're

00:01:28.320 --> 00:01:29.450
flowing past each other.

00:01:29.450 --> 00:01:32.610
The hydrogen bonds are
giving that cohesiveness.

00:01:32.610 --> 00:01:34.670
The molecules are attracted to each other.

00:01:34.670 --> 00:01:37.420
But if you look at the
molecules on the surface,

00:01:37.420 --> 00:01:38.750
if you look at the ones on the surface,

00:01:38.750 --> 00:01:41.150
sure, they might have
stuff pulling down on them,

00:01:41.150 --> 00:01:44.620
they might have stuff
pulling them to the side,

00:01:44.620 --> 00:01:48.220
but they don't have anything
pulling on them from above.

00:01:48.220 --> 00:01:50.120
And because of this, you could imagine

00:01:50.120 --> 00:01:52.790
that they're able to get a
little bit more densely packed,

00:01:52.790 --> 00:01:55.420
that they're able to get a
little closer to their neighbors.

00:01:55.420 --> 00:01:57.690
And this is what allows
them to actually have

00:01:57.690 --> 00:02:01.120
a stronger, I guess you could
say, intermolecular force

00:02:01.120 --> 00:02:04.110
at the surface than you
have within the body,

00:02:04.110 --> 00:02:08.090
and that causes a phenomenon
known as surface tension.

00:02:08.090 --> 00:02:12.800
So you have stronger, you
have kind of a deeper,

00:02:12.800 --> 00:02:14.450
and this is still just hydrogen bonds,

00:02:14.450 --> 00:02:15.450
but since they're not being pulled

00:02:15.450 --> 00:02:17.590
in other directions
by, upwards by the air,

00:02:17.590 --> 00:02:20.020
they're able to get a little
bit more closely packed,

00:02:20.020 --> 00:02:21.950
a little bit tighter, and this we refer to

00:02:21.950 --> 00:02:26.950
as surface tension, surface tension.

00:02:27.090 --> 00:02:29.820
And you have probably
observed surface tension

00:02:29.820 --> 00:02:32.150
many, many, many times in your life

00:02:32.150 --> 00:02:35.320
in the form of, say, a water droplet.

00:02:35.320 --> 00:02:40.320
A water droplet, it's able to
have this roughly round shape

00:02:40.450 --> 00:02:42.350
because all the little water molecules

00:02:42.350 --> 00:02:44.790
on the surface of the water droplet,

00:02:44.790 --> 00:02:46.090
and here the surface might even be

00:02:46.090 --> 00:02:47.520
on the bottom of the water droplet.

00:02:47.520 --> 00:02:48.820
They are more attracted to each other

00:02:48.820 --> 00:02:50.820
than they are to the surrounding air,

00:02:50.820 --> 00:02:53.220
so they're able to form
this type of a shape.

00:02:53.220 --> 00:02:55.190
You might've seen it if you go to a pond

00:02:55.190 --> 00:02:57.950
or a stream sometimes, so
you see some still water.

00:02:57.950 --> 00:03:00.550
And let's say, let me do this in blue.

00:03:00.550 --> 00:03:03.350
So let's say that this is the surface

00:03:03.350 --> 00:03:05.550
of the water right over here.

00:03:05.550 --> 00:03:07.850
You might have seen
insects that are able to

00:03:07.850 --> 00:03:09.880
walk on the surface of the water.

00:03:09.880 --> 00:03:11.520
And I'm not doing a great
job at drawing the insects.

00:03:11.520 --> 00:03:12.950
They don't look exactly like that.

00:03:12.950 --> 00:03:14.790
But they can walk on the
surface of the water.

00:03:14.790 --> 00:03:17.020
You might've seen or
you might've even tried

00:03:17.020 --> 00:03:19.050
to do something like put
a paperclip on the water.

00:03:19.050 --> 00:03:20.820
And even though this thing
is actually more dense

00:03:20.820 --> 00:03:22.690
than the water and you
might expect it to sink,

00:03:22.690 --> 00:03:24.320
but because of the surface tension,

00:03:24.320 --> 00:03:27.390
which really forms something
of a film on top of the water,

00:03:27.390 --> 00:03:29.490
the thing won't penetrate the surface,

00:03:29.490 --> 00:03:32.220
so the paperclip will
float, unless you were to

00:03:32.220 --> 00:03:34.120
push on it a little bit and it allow it

00:03:34.120 --> 00:03:35.850
to puncture the surface, and then

00:03:35.850 --> 00:03:38.050
it would actually sink, which
is what you would expect

00:03:38.050 --> 00:03:40.580
because it is actually denser.

00:03:40.580 --> 00:03:43.390
You'd even see this if
you were to take a cup,

00:03:43.390 --> 00:03:46.510
if you were to take a cup
and you were to fill it

00:03:46.510 --> 00:03:49.190
all the way up to the rim
and then a little bit higher,

00:03:49.190 --> 00:03:51.150
it won't immediately overflow.

00:03:51.150 --> 00:03:52.320
It won't immediately overflow.

00:03:52.320 --> 00:03:53.450
If you're very careful, you'll see

00:03:53.450 --> 00:03:54.990
that you form a bulge here.

00:03:54.990 --> 00:03:57.480
And that bulges because those
individual water molecules

00:03:57.480 --> 00:03:59.690
are more attracted to each other

00:03:59.690 --> 00:04:02.020
than they are to the surrounding air.

00:04:02.020 --> 00:04:04.610
So that allows for
something of a little bulge.

00:04:04.610 --> 00:04:06.200
Obviously if you keep
pouring water, at some point,

00:04:06.200 --> 00:04:07.790
they're just gonna start overflowing

00:04:07.790 --> 00:04:09.310
because gravity's gonna take over there.

00:04:09.310 --> 00:04:11.880
Gravity's gonna overwhelm
the surface tension.

00:04:11.880 --> 00:04:16.220
But this bulge will actually form.

00:04:16.220 --> 00:04:18.390
So surface tension, it is really due to

00:04:18.390 --> 00:04:20.170
the cohesion of the water.

00:04:20.170 --> 00:04:21.650
Remember, cohesion is when the molecules

00:04:21.650 --> 00:04:23.490
are attracted to each other.

00:04:23.490 --> 00:04:25.190
And it definitely, and
especially because they're

00:04:25.190 --> 00:04:29.090
more attracted to each other
than the surrounding air.


Heat of vaporization of water and ethanol

WEBVTT
Kind: captions
Language: en

00:00:00.000 --> 00:00:02.191
- [Voiceover] So we have two
different substances here

00:00:02.191 --> 00:00:03.564
and just for the sake of an argument,

00:00:03.564 --> 00:00:05.736
let's assume that they
are in their liquid state.

00:00:05.736 --> 00:00:07.702
Well you probably already recognize

00:00:07.702 --> 00:00:08.976
this substance right here,

00:00:08.976 --> 00:00:10.847
each molecule has one oxygen atom and two

00:00:10.847 --> 00:00:14.318
hydrogen atoms, this is
water and we have drawn all

00:00:14.318 --> 00:00:16.504
neat hydrogen bonds right over there.

00:00:16.504 --> 00:00:18.118
Now this substance, at least right now,

00:00:18.118 --> 00:00:19.777
might be a little less familiar to you,

00:00:19.777 --> 00:00:21.633
you might recognize you have an O-H group,

00:00:21.633 --> 00:00:23.909
and then you have a carbon chain,

00:00:23.909 --> 00:00:25.268
this tells you that this is an alcohol,

00:00:25.268 --> 00:00:26.370
and what type of alcohol?

00:00:26.370 --> 00:00:28.030
Well you have two carbons here,

00:00:28.030 --> 00:00:31.437
so this is ethyl alcohol
or known as ethanol.

00:00:31.437 --> 00:00:34.296
So this right over here,
let me write that down.

00:00:34.296 --> 00:00:38.255
This is ethanol, which is
the primary constituent in

00:00:38.255 --> 00:00:41.494
the alcohol that people drink,
it's also an additive into

00:00:41.494 --> 00:00:45.709
car fuel, but what I
wanna think about here,

00:00:45.709 --> 00:00:47.601
is if we assume that both of these are

00:00:47.601 --> 00:00:49.731
in their liquid state and let's say

00:00:49.731 --> 00:00:51.391
they're hanging out in a cup

00:00:51.391 --> 00:00:53.445
and we're just at sea level

00:00:53.445 --> 00:00:56.348
so it's just a standard
pressure conditions.

00:00:56.348 --> 00:01:00.746
Which one is going to
be easier to vaporize

00:01:00.746 --> 00:01:02.570
or which one is going to have more

00:01:02.570 --> 00:01:04.276
of it's molecules turning into vapor,

00:01:04.276 --> 00:01:06.633
or I guess you could say
turning into vapor more easily?

00:01:06.633 --> 00:01:09.837
Well you immediately see that
they both have hydrogen bonds,

00:01:09.837 --> 00:01:11.381
you have this hydrogen bond between the

00:01:11.381 --> 00:01:13.973
partially negative end and
the partial positive ends,

00:01:13.973 --> 00:01:16.213
hydrogen bond between
the partial negative end

00:01:16.213 --> 00:01:17.792
and the partial positive ends.

00:01:17.792 --> 00:01:19.033
The other thing that you notice is that,

00:01:19.033 --> 00:01:21.459
I guess you could think of
it on a per molecule basis,

00:01:21.459 --> 00:01:23.493
on average you have fewer hydrogen bonds

00:01:23.493 --> 00:01:25.593
on the ethanol than you have on the water.

00:01:25.593 --> 00:01:28.136
Ethanol-- Oxygen is more electronegative,

00:01:28.136 --> 00:01:29.900
we already know it's more
electronegative than hydrogen,

00:01:29.900 --> 00:01:31.792
it's also more
electronegative than carbon,

00:01:31.792 --> 00:01:34.011
but it's a lot more
electronegative than hydrogen.

00:01:34.011 --> 00:01:35.519
So you have this imbalance here

00:01:35.519 --> 00:01:36.877
and then on top of that, this carbon,

00:01:36.877 --> 00:01:38.887
you have a lot more atoms here in which

00:01:38.887 --> 00:01:40.882
to distribute a partial charge.

00:01:40.882 --> 00:01:42.426
There could be a very weak partial charge

00:01:42.426 --> 00:01:44.504
distributed here amongst the carbons

00:01:44.504 --> 00:01:46.652
but you have a stronger
partial charge on the hydrogen

00:01:46.652 --> 00:01:48.707
but it's not gonna be
strong as what you have here

00:01:48.707 --> 00:01:50.646
because, once again, you
have a larger molecule

00:01:50.646 --> 00:01:53.641
to distribute especially
around this carbon

00:01:53.641 --> 00:01:55.870
to help dissipate charging.

00:01:55.870 --> 00:01:58.400
So you're gonna have
weaker partial charges here

00:01:58.400 --> 00:02:01.071
and they're occurring in fewer places

00:02:01.071 --> 00:02:03.404
so you have less hydrogen
bonding on the ethanol

00:02:03.404 --> 00:02:05.761
than you have on the water.

00:02:05.761 --> 00:02:10.721
Let me write that, you
have less hydrogen bonding.

00:02:10.721 --> 00:02:12.557
As we've already talked about,

00:02:12.557 --> 00:02:15.158
in the liquid state and frankly,
in the solid state as well,

00:02:15.158 --> 00:02:17.340
the hydrogen bonding is what is keeping

00:02:17.340 --> 00:02:19.128
these things together,
that's what's keeping the

00:02:19.128 --> 00:02:21.368
water together, flowing
next to each other.

00:02:21.368 --> 00:02:23.400
This is what's keeping
the ethanol together.

00:02:23.400 --> 00:02:26.801
So if you have less hydrogen--
Let me write this down,

00:02:26.801 --> 00:02:30.079
less hydrogen bonding, it
actually has more hydrogen atoms

00:02:30.079 --> 00:02:32.349
per molecule, but if you
have less hydrogen bonding,

00:02:32.349 --> 00:02:35.369
it's gonna take less energy
to break these things free.

00:02:35.369 --> 00:02:37.968
Before I even talk about
breaking things free and these

00:02:37.968 --> 00:02:40.753
molecules turning into vapors
entering their gas state,

00:02:40.753 --> 00:02:43.112
let's just think about how that happens.

00:02:43.112 --> 00:02:45.514
When we talk about the
temperature of a system,

00:02:45.514 --> 00:02:48.116
we're really just talking about
the average kinetic energy.

00:02:48.116 --> 00:02:50.471
Each molecule, remember
they're all bouncing around

00:02:50.471 --> 00:02:53.153
in all different ways, this
one might have, for example,

00:02:53.153 --> 00:02:55.726
a much higher kinetic
energy than this one.

00:02:55.726 --> 00:02:57.194
They're all moving in
different directions,

00:02:57.194 --> 00:02:58.515
this one might have a little bit higher,

00:02:58.515 --> 00:03:00.234
and maybe this one all of a sudden has

00:03:00.234 --> 00:03:02.231
a really high kinetic energy
because it's just been

00:03:02.231 --> 00:03:04.413
knocked in just the exact right ways

00:03:04.413 --> 00:03:07.768
and it's enough to overcome
both these hydrogen bonds

00:03:07.768 --> 00:03:11.065
over here and the pressure
from the air above it.

00:03:11.065 --> 00:03:13.558
Remember this isn't happening
in a vacuum, you have

00:03:13.558 --> 00:03:17.380
air up here, air molecules,
I'll just draw the generic,

00:03:17.380 --> 00:03:18.772
you have different types of things,

00:03:18.772 --> 00:03:20.956
nitrogen, carbon dioxide,
etcetera etcetera.

00:03:20.956 --> 00:03:23.161
But if I just draw generic air molecules,

00:03:23.161 --> 00:03:26.295
there's also some pressure from
these things bouncing around

00:03:26.295 --> 00:03:29.824
but this one might have enough,
this particular molecule

00:03:29.824 --> 00:03:32.180
might have enough kinetic
energy to overcome the hydrogen

00:03:32.180 --> 00:03:35.373
bonds and overcome the pressure
from the molecules above it

00:03:35.373 --> 00:03:39.530
to essentially vaporize,
to turn into its gas state.

00:03:39.530 --> 00:03:41.492
The same thing might be true over here,

00:03:41.492 --> 00:03:43.302
maybe this is the molecule that has

00:03:43.302 --> 00:03:46.367
the super high kinetic energy
to be able to break free.

00:03:46.367 --> 00:03:50.825
In that case, it is going to
turn into its gaseous state.

00:03:50.825 --> 00:03:52.748
The hydrogen bonds are gonna break apart,

00:03:52.748 --> 00:03:55.443
and it's gonna be so far from
any of its sibling molecules,

00:03:55.443 --> 00:03:57.773
I guess you could say, from
the other ethanol molecules

00:03:57.773 --> 00:04:00.144
that it won't be able to
form new hydrogen bonds.

00:04:00.144 --> 00:04:02.143
Same thing with this
one, once it vaporizes,

00:04:02.143 --> 00:04:04.764
it's out in gaseous state, it's
much further from any other

00:04:04.764 --> 00:04:06.388
water molecules, it's not going to be able

00:04:06.388 --> 00:04:08.212
to form those hydrogen bonds with them.

00:04:08.212 --> 00:04:11.022
Because there's more
hydrogen bonds here to break,

00:04:11.022 --> 00:04:13.483
than here, you can imagine
it would take, on average,

00:04:13.483 --> 00:04:18.138
more heat to vaporize this thing
than to vaporize this thing

00:04:18.138 --> 00:04:20.553
and that is indeed the case.

00:04:20.553 --> 00:04:23.999
The term for how much heat do you need to

00:04:23.999 --> 00:04:27.157
vaporize a certain mass of a
substance, you can imagine,

00:04:27.157 --> 00:04:30.756
is called the heat of vaporization,
let me write that down,

00:04:30.756 --> 00:04:35.756
heat of vaporization and you can imagine,

00:04:37.962 --> 00:04:41.909
it is higher for water
than it is for ethanol

00:04:41.909 --> 00:04:43.395
and I will give you the numbers here,

00:04:43.395 --> 00:04:44.776
at least ones that I've
been able to look up.

00:04:44.776 --> 00:04:46.528
I found slightly different numbers,

00:04:46.528 --> 00:04:49.283
depending on which resource
I looked at but what I found

00:04:49.283 --> 00:04:54.283
for water, the heat of vaporization
is 2260 joules per gram

00:04:56.318 --> 00:04:58.896
or instead of using joules,
remember joules is a unit of

00:04:58.896 --> 00:05:01.438
energy it could be a unit of
heat, instead of joules if you

00:05:01.438 --> 00:05:02.854
wanna think of it in terms of calories,

00:05:02.854 --> 00:05:07.854
that's equivalent to 541
calories per gram while the

00:05:10.206 --> 00:05:13.561
heat of vaporization for
ethanol is a good bit lower.

00:05:13.561 --> 00:05:16.011
The heat of vaporization for
ethanol--let me make this clear

00:05:16.011 --> 00:05:20.984
this right over here is
water, that's for water.

00:05:20.984 --> 00:05:23.417
The same thing for ethanol.

00:05:23.417 --> 00:05:27.295
The heat of vaporization for ethanol is,

00:05:27.295 --> 00:05:32.295
based on what I looked
up, is 841 joules per gram

00:05:32.484 --> 00:05:37.484
or if we wanna write them as
calories, 201 calories per gram

00:05:38.788 --> 00:05:40.809
which means it would require, roughly,

00:05:40.809 --> 00:05:45.150
201 calories to evaporate,
to fully vaporize

00:05:45.150 --> 00:05:50.150
a gram of ethanol at standard temperature,

00:05:50.768 --> 00:05:52.685
keeping the temperature constant.

00:05:52.685 --> 00:05:54.286
We could talk more about
that in other videos,

00:05:54.286 --> 00:05:56.782
but the big thing that
we're talking about here

00:05:56.782 --> 00:05:59.707
is, look, it requires less
energy to vaporize this thing

00:05:59.707 --> 00:06:02.911
and you can run the experiment,
take a glass of water,

00:06:02.911 --> 00:06:04.861
equivalent glasses, fill them
up the same amount of time,

00:06:04.861 --> 00:06:08.229
a glass of water and a glass of ethanol

00:06:08.229 --> 00:06:10.707
and then see how long it takes.

00:06:10.707 --> 00:06:12.526
You can put a heat lamp on top of them

00:06:12.526 --> 00:06:13.835
or you could just put them outside

00:06:13.835 --> 00:06:15.449
where they're experiencing the same

00:06:15.449 --> 00:06:18.314
atmospheric conditions,
the same sun's rays

00:06:18.314 --> 00:06:22.049
and see what's the difference--
how much more energy,

00:06:22.049 --> 00:06:23.989
how much more time does it take for

00:06:23.989 --> 00:06:26.276
the water to evaporate than the ethanol.

00:06:26.276 --> 00:06:28.877
There's a similar idea here
which is boiling point.

00:06:28.877 --> 00:06:30.908
We've all boiled things, boiling point is

00:06:30.908 --> 00:06:35.877
the point at which the vapor
pressure from the substance

00:06:35.877 --> 00:06:40.877
has become equal to and starts
to overcome the pressure

00:06:40.937 --> 00:06:43.841
from just a regular atmospheric pressure.

00:06:43.841 --> 00:06:45.720
And so you can imagine that water

00:06:45.720 --> 00:06:48.274
has a higher temperature
at which it starts

00:06:48.274 --> 00:06:50.876
to boil than ethanol and
that is indeed the case.

00:06:50.876 --> 00:06:55.275
Water's boiling point is
exactly 100° Celsius, in fact,

00:06:55.275 --> 00:06:58.154
water's boiling point was
an important data point for

00:06:58.154 --> 00:07:01.057
even establishing the Celsius
scale, so by definition,

00:07:01.057 --> 00:07:04.238
it's 100° Celsius, while
ethanol's boiling point is

00:07:04.238 --> 00:07:07.465
approximately 78° Celsius.

00:07:07.465 --> 00:07:09.763
So it boils at a much lower temperature

00:07:09.763 --> 00:07:11.260
an that's because there's just fewer

00:07:11.260 --> 00:07:14.763
hydrogen bonds to actually break.


Evaporative cooling

WEBVTT
Kind: captions
Language: en

00:00:00.000 --> 00:00:01.803
- [Voiceover] So if you
are like most of us,

00:00:01.803 --> 00:00:05.338
your body probably sweats when it is warm,

00:00:05.338 --> 00:00:06.618
when your environment is warm,

00:00:06.618 --> 00:00:08.731
and you probably realize that it sweats

00:00:08.731 --> 00:00:10.316
in order to cool itself,

00:00:10.316 --> 00:00:12.632
in order to keep the
body from overheating.

00:00:12.632 --> 00:00:14.400
But you probably have wondered,

00:00:14.400 --> 00:00:15.558
"Well, how does this work?

00:00:15.558 --> 00:00:17.142
"What is actually causing that?"

00:00:17.142 --> 00:00:20.413
And the simple answer is it's happening--

00:00:20.413 --> 00:00:22.283
or what's allowing your body to cool--

00:00:22.283 --> 00:00:24.874
the chemical process,
I guess you could say

00:00:24.874 --> 00:00:26.276
the physical process is happening

00:00:26.276 --> 00:00:27.881
is evaporative cooling.

00:00:27.881 --> 00:00:31.457
Evaporative cooling.

00:00:31.457 --> 00:00:34.170
Which is really the
notion that as that water,

00:00:34.170 --> 00:00:36.120
those beats of sweat vaporize,

00:00:36.120 --> 00:00:38.132
it's actually gonna cool your arm down.

00:00:38.132 --> 00:00:40.062
But that begs the question,

00:00:40.062 --> 00:00:41.951
how does that actually happen?

00:00:41.951 --> 00:00:44.247
And so let's just
visualize it a little bit.

00:00:44.247 --> 00:00:46.482
Let's just say that is your arm,

00:00:46.482 --> 00:00:49.245
so this is your arm right
over here, so let's...

00:00:49.245 --> 00:00:50.566
I don't draw my best...

00:00:50.566 --> 00:00:52.659
Draw a quick arm right over here,

00:00:52.659 --> 00:00:55.869
so okay, that's your arm,
and it's got beads of sweat.

00:00:55.869 --> 00:00:57.047
Let's say it's a hot environment

00:00:57.047 --> 00:01:00.135
it's got beads of sweat right over here.

00:01:00.135 --> 00:01:02.370
And if we were to zoom in on that sweat,

00:01:02.370 --> 00:01:04.849
if we were to zoom in on that sweat,

00:01:04.849 --> 00:01:07.815
we would see the
constituent water molecules

00:01:07.815 --> 00:01:10.842
and sweat is mainly H20.

00:01:10.842 --> 00:01:12.122
It is mainly water.

00:01:12.122 --> 00:01:14.581
Now when we talk about the
temperature of something,

00:01:14.581 --> 00:01:16.673
we're talking about the
average kinetic energy.

00:01:16.673 --> 00:01:17.973
Each of the individual molecules,

00:01:17.973 --> 00:01:19.477
they all have different kinetic energies.

00:01:19.477 --> 00:01:20.940
They're all bouncing
around in different ways

00:01:20.940 --> 00:01:23.154
and transferring the momentum
in all different ways.

00:01:23.154 --> 00:01:25.288
And so you can imagine a reality.

00:01:25.288 --> 00:01:27.218
Maybe this one has a
fairly high kinetic energy.

00:01:27.218 --> 00:01:28.295
It's moving in that direction.

00:01:28.295 --> 00:01:29.839
This one has a lower kinetic energy.

00:01:29.839 --> 00:01:30.931
moving in this direction.

00:01:30.931 --> 00:01:32.800
Maybe this one has a
medium kinetic energy,

00:01:32.800 --> 00:01:33.958
moving in this direction.

00:01:33.958 --> 00:01:36.254
Maybe this one has a
really high kinetic energy

00:01:36.254 --> 00:01:38.143
moving in that direction.

00:01:38.143 --> 00:01:40.012
And so we've already talked about

00:01:40.012 --> 00:01:41.614
how hydrogen bonds in water

00:01:41.614 --> 00:01:43.117
between the partially negative end

00:01:43.117 --> 00:01:44.275
and the partially positive ends.

00:01:44.275 --> 00:01:45.860
That's what keeps the water together

00:01:45.860 --> 00:01:48.135
as these things move past
and flow past each other.

00:01:48.135 --> 00:01:49.781
What gives the water its cohesion

00:01:49.781 --> 00:01:51.528
is these hydrogen bonds.

00:01:51.528 --> 00:01:52.890
But if all of a sudden--

00:01:52.890 --> 00:01:54.657
remember, we're talking about
the average kinetic energy--

00:01:54.657 --> 00:01:56.425
but even if we're at room temperature,

00:01:56.425 --> 00:01:58.985
and the average kinetic
energy isn't so hot,

00:01:58.985 --> 00:02:00.955
you might have individual particles,

00:02:00.955 --> 00:02:02.540
individual molecules that actually have

00:02:02.540 --> 00:02:03.942
quite a high kinetic energy

00:02:03.942 --> 00:02:05.141
and if they're in the right place,

00:02:05.141 --> 00:02:08.493
if they're near the surface
and their kinetic energy

00:02:08.493 --> 00:02:12.130
is high enough to break the hydrogen bonds

00:02:12.130 --> 00:02:14.202
with neighboring water molecules,

00:02:14.202 --> 00:02:16.437
and to overcome the
pressure in the atmosphere,

00:02:16.437 --> 00:02:19.119
so let's say that this is,
these are just gas molecules

00:02:19.119 --> 00:02:20.683
in the atmosphere here.

00:02:20.683 --> 00:02:22.938
But it's enough to break
free and none of these things

00:02:22.938 --> 00:02:24.462
bounce into it and force it back

00:02:24.462 --> 00:02:25.702
to form hydrogen bonds.

00:02:25.702 --> 00:02:29.034
This thing could actually break free

00:02:29.034 --> 00:02:32.284
and enter and become water vapor.

00:02:32.284 --> 00:02:34.317
And become in its gaseous state.

00:02:34.317 --> 00:02:36.978
And it'll be so far apart
from other water molecules

00:02:36.978 --> 00:02:39.091
that it won't form hydrogen bonds anymore.

00:02:39.091 --> 00:02:43.763
So by vaporizing or by this
process of evaporation,

00:02:43.763 --> 00:02:44.495
what's happening?

00:02:44.495 --> 00:02:48.761
Well if your highest
kinetic energy particles

00:02:48.761 --> 00:02:52.012
or some of your highest
kinetic energy particles

00:02:52.012 --> 00:02:54.430
are able to escape, what's going to happen

00:02:54.430 --> 00:02:56.177
to the average kinetic energy?

00:02:56.177 --> 00:03:00.484
Well as the highest kinetic
energy things escape

00:03:00.484 --> 00:03:02.475
and those are the ones that
are most likely to escape,

00:03:02.475 --> 00:03:05.677
well then your average kinetic
energy is going to go down.

00:03:05.677 --> 00:03:09.222
So average kinetic energy

00:03:09.222 --> 00:03:10.828
is going to go down.

00:03:10.828 --> 00:03:12.026
Or another way of saying it,

00:03:12.026 --> 00:03:14.220
is that your temperature
is going to go down.

00:03:14.220 --> 00:03:16.496
Your temperature is going to go down

00:03:16.496 --> 00:03:20.336
because as these molecules
turn into water vapor,

00:03:20.336 --> 00:03:22.550
they're going to be the
highest kinetic energy,

00:03:22.550 --> 00:03:24.623
energy is transferred to
them, and then they escape.

00:03:24.623 --> 00:03:26.228
And so what's left over is going

00:03:26.228 --> 00:03:28.483
to have a lower average kinetic energy.

00:03:28.483 --> 00:03:29.824
And you're saying, "Well, how does that

00:03:29.824 --> 00:03:31.978
"actually cool down my hand?"

00:03:31.978 --> 00:03:35.635
Well, your hand is made
up of molecules as well.

00:03:35.635 --> 00:03:38.642
So let's say this is the
surface of your hand,

00:03:38.642 --> 00:03:39.535
those are the molecules,

00:03:39.535 --> 00:03:41.547
they have some average kinetic energy,

00:03:41.547 --> 00:03:43.721
they are kind of vibrating in place,

00:03:43.721 --> 00:03:45.062
especially if we're
talking about they're...

00:03:45.062 --> 00:03:46.159
they're a solid.

00:03:46.159 --> 00:03:48.190
And so maybe I'll draw the more,

00:03:48.190 --> 00:03:50.100
you know, they're vibrating like this,

00:03:50.100 --> 00:03:52.213
they're bonded to each other in some way.

00:03:52.213 --> 00:03:54.550
I won't go into the details of what types

00:03:54.550 --> 00:03:55.769
of molecules these are,

00:03:55.769 --> 00:03:57.597
but then if you have your
water molecules here,

00:03:57.597 --> 00:03:59.771
water molecules that are
sitting on the surface,

00:03:59.771 --> 00:04:02.189
and I'm drawing this is
kind of a cross-section.

00:04:02.189 --> 00:04:03.956
Let me draw the water molecules.

00:04:03.956 --> 00:04:06.029
I'll draw them as blue molecules.

00:04:06.029 --> 00:04:07.675
So this is an H2O right over here.

00:04:07.675 --> 00:04:11.364
H2O. This is an H2O.

00:04:11.364 --> 00:04:13.782
And this is an H2O.

00:04:13.782 --> 00:04:15.651
And they have some hydrogen bonding,

00:04:15.651 --> 00:04:18.373
so there is some hydrogen
bonding going on.

00:04:18.373 --> 00:04:22.924
Well, as the high kinetic
energy water molecules escape,

00:04:22.924 --> 00:04:25.504
I'll say this one right over here escapes,

00:04:25.504 --> 00:04:27.496
and so the average kinetic energy

00:04:27.496 --> 00:04:29.995
of what's left over is lower,

00:04:29.995 --> 00:04:32.209
so then the temperature has gone down,

00:04:32.209 --> 00:04:34.566
and now your body molecules,

00:04:34.566 --> 00:04:36.496
the ones that are all warmed up,

00:04:36.496 --> 00:04:38.548
and because of whatever's
going on inside of your body,

00:04:38.548 --> 00:04:40.925
well, those can now bump into,

00:04:40.925 --> 00:04:43.058
they can vibrate and bump
into these water molecules

00:04:43.058 --> 00:04:44.704
and increase their kinetic energy

00:04:44.704 --> 00:04:46.350
more than the ones that have
the most kinetic energy.

00:04:46.350 --> 00:04:47.670
Those might escape again.

00:04:47.670 --> 00:04:49.235
And so it's a--one way
of thinking about it

00:04:49.235 --> 00:04:51.063
is that all that heat is being used

00:04:51.063 --> 00:04:53.217
to allow these individual water molecules

00:04:53.217 --> 00:04:55.127
to escape in order to vaporize.

00:04:55.127 --> 00:04:57.930
And so that heat is leaving your body,

00:04:57.930 --> 00:04:59.434
so it allows you to cool down.

00:04:59.434 --> 00:05:02.908
Cooling down happens by
heat actually leaving.

00:05:02.908 --> 00:05:04.737
So that's how evaporative...

00:05:04.737 --> 00:05:06.037
I wrote evaporative cool...

00:05:06.037 --> 00:05:07.987
That's how evaporative cooling...

00:05:07.987 --> 00:05:11.238
That's how evaporative
cooling actually works.


Specific heat of water

WEBVTT
Kind: captions
Language: en

00:00:00.464 --> 00:00:03.088
- [Voiceover] In chemistry,
there's a very valuable concept

00:00:03.088 --> 00:00:06.966
called Specific Heat, and
specific heat is particular

00:00:06.966 --> 00:00:08.289
to a given substance.

00:00:08.289 --> 00:00:10.820
Every substance has a
different specific heat.

00:00:10.820 --> 00:00:13.792
It's defined as the amount of heat,

00:00:13.792 --> 00:00:16.044
the amount of heat energy needed

00:00:16.044 --> 00:00:20.177
to raise one gram of a
substance one degree celsius.

00:00:20.177 --> 00:00:21.454
Sometimes the definition might say

00:00:21.454 --> 00:00:24.705
to raise a given mass of a
substance one degree celsius,

00:00:24.705 --> 00:00:27.259
but I'm just being a
little bit more particular.

00:00:27.259 --> 00:00:31.113
One gram of a substance,
one degree celsius.

00:00:31.113 --> 00:00:32.669
So this is telling us,
well how much energy

00:00:32.669 --> 00:00:35.153
do I have to put into
something to heat it up?

00:00:35.153 --> 00:00:36.500
So, for example.

00:00:36.500 --> 00:00:39.472
For example, water, water.

00:00:39.472 --> 00:00:41.748
If I wanna raise that one degree celsius,

00:00:41.748 --> 00:00:45.648
so if I wanna raise
that one degree celsius,

00:00:45.648 --> 00:00:47.320
I would have to put in,

00:00:47.320 --> 00:00:50.432
I would have to put in
a certain amount of,

00:00:50.432 --> 00:00:52.312
I would have to put in a
certain amount of heat,

00:00:52.312 --> 00:00:55.470
which would be different
than, say if I had sand.

00:00:55.470 --> 00:00:59.110
Let's say this is, let's say this is sand.

00:00:59.510 --> 00:01:00.694
This is sand.

00:01:00.694 --> 00:01:02.389
I have trouble picking colors.

00:01:02.389 --> 00:01:04.665
So this is sand right over here.

00:01:04.665 --> 00:01:06.499
I have to do a better job of drawing sand.

00:01:06.499 --> 00:01:08.589
So this is sand right over here.

00:01:08.589 --> 00:01:11.421
If I wanna raise that one degree celsius,

00:01:12.203 --> 00:01:13.216
I would need a different amount.

00:01:13.216 --> 00:01:15.515
It actually turns out
that I need less heat,

00:01:15.515 --> 00:01:18.394
I need less heat to raise
the sand one degree celsius

00:01:18.394 --> 00:01:21.853
than I need to raise the
temperature of the water

00:01:21.853 --> 00:01:24.802
or one gram of the water
one degree celsius.

00:01:24.802 --> 00:01:26.033
So let's say this is a gram of water

00:01:26.033 --> 00:01:27.240
and this is a gram of sand.

00:01:27.240 --> 00:01:29.400
I'm going to need more heat here

00:01:29.400 --> 00:01:32.704
to raise this one degree
celsius than to raise that.

00:01:32.704 --> 00:01:35.335
That's because water has
a higher specific heat.

00:01:35.335 --> 00:01:37.163
So higher,

00:01:37.471 --> 00:01:40.573
higher, relatively higher specific heat.

00:01:40.573 --> 00:01:43.308
Specific heat.

00:01:43.684 --> 00:01:45.728
And sand, or at least relative to water,

00:01:45.728 --> 00:01:47.626
has a lower specific heat.

00:01:47.817 --> 00:01:49.837
Lower specific heat.

00:01:49.837 --> 00:01:51.277
So two ways you could think about it.

00:01:51.617 --> 00:01:52.777
Let me write this.

00:01:52.777 --> 00:01:54.077
Lower,

00:01:54.077 --> 00:01:56.684
lower specific,

00:01:56.684 --> 00:01:59.238
specific heat.

00:01:59.238 --> 00:02:00.283
Two ways to think about it.

00:02:00.283 --> 00:02:02.187
If you wanna raise one
gram of each of them

00:02:02.187 --> 00:02:05.124
one degree celsius, you're
gonna have to put more energy

00:02:05.124 --> 00:02:07.008
into the water than you're going to have

00:02:07.008 --> 00:02:08.308
to put into the sand.

00:02:08.308 --> 00:02:10.143
Or the other way around,
if you put the same amount

00:02:10.143 --> 00:02:12.697
of energy into both, you're
gonna raise the temperature

00:02:12.697 --> 00:02:15.785
of the sand a lot more than
you would raise the temperature

00:02:15.785 --> 00:02:17.201
of the water.

00:02:17.201 --> 00:02:20.359
And water, actually, its
specific heat has a special name

00:02:20.359 --> 00:02:22.008
and this is a name that
you have seen before.

00:02:22.008 --> 00:02:24.817
The specific heat of water
is called the calorie.

00:02:24.817 --> 00:02:26.212
Specific,

00:02:27.286 --> 00:02:30.453
specific heat

00:02:30.453 --> 00:02:32.324
of water

00:02:32.324 --> 00:02:34.605
is called the calorie.

00:02:34.605 --> 00:02:36.184
And you have seen this word before.

00:02:36.184 --> 00:02:38.251
When you've wanted to cut calories,

00:02:38.251 --> 00:02:39.319
when you've looked at the back

00:02:39.319 --> 00:02:42.059
of nutritional labels on food.

00:02:42.059 --> 00:02:43.405
There's one clarification.

00:02:43.405 --> 00:02:44.729
The calorie that people talk about

00:02:44.729 --> 00:02:46.067
when they're talking
about nutritional labels

00:02:46.067 --> 00:02:48.087
or how many calories are actually in food,

00:02:48.087 --> 00:02:49.921
that's actually kilocalories.

00:02:49.921 --> 00:02:52.684
So if you see, if someone hands you

00:02:52.684 --> 00:02:54.983
a, let's say a bowl of ice cream.

00:02:54.983 --> 00:02:56.841
Let me draw a bowl of ice cream here.

00:02:56.841 --> 00:02:59.975
So if someone hands you a bowl
of ice cream right over here

00:02:59.975 --> 00:03:03.313
and they tell you that
this is 500 calories.

00:03:03.551 --> 00:03:04.665
Let me write that down.

00:03:04.665 --> 00:03:07.864
This is 500 calories.

00:03:07.864 --> 00:03:10.627
If we're thinking of it
in terms of specific heat,

00:03:10.627 --> 00:03:13.181
it's actually 500 kilocalories.

00:03:13.181 --> 00:03:17.146
500 kilocalories.

00:03:17.500 --> 00:03:18.367
So there's a couple of ways

00:03:18.367 --> 00:03:20.805
that you could think
about 500 kilocalories.

00:03:20.805 --> 00:03:22.709
You could think about it as,

00:03:22.709 --> 00:03:27.379
this is, this ice cream
has enough energy to raise,

00:03:27.379 --> 00:03:32.157
to raise 500 kilograms

00:03:32.157 --> 00:03:34.499
of water

00:03:35.030 --> 00:03:37.282
one degree celsius.

00:03:37.282 --> 00:03:40.487
You could also view it as the amount,

00:03:40.487 --> 00:03:41.555
well actually if you wanna think of it

00:03:41.555 --> 00:03:45.432
in more human terms, most
humans are roughly grown people

00:03:45.432 --> 00:03:46.965
are between 50 kilograms

00:03:46.965 --> 00:03:49.078
or 60, 70 kilograms roughly over there.

00:03:49.078 --> 00:03:51.051
You could say 50 kilograms of water.

00:03:51.051 --> 00:03:52.444
Actually a grown male might be composed

00:03:52.444 --> 00:03:54.047
of about 50 kilograms of water

00:03:54.047 --> 00:03:55.138
and then there's obviously other things

00:03:55.138 --> 00:03:57.553
that make up their weight,
I'm just approximating.

00:03:57.553 --> 00:04:01.407
50 kilograms of water

00:04:02.276 --> 00:04:03.730
and then we're raising
it one degree celsius

00:04:03.730 --> 00:04:07.375
in the top case, but in this
case you would raise it 10.

00:04:07.375 --> 00:04:10.185
You would raise it 10 degrees celsius.

00:04:10.185 --> 00:04:11.625
And that's actually happening in our body.

00:04:11.625 --> 00:04:14.132
Your body heat is actually
caused, partially,

00:04:14.132 --> 00:04:17.197
the energy from food, some of
it is to process your movement

00:04:17.197 --> 00:04:19.519
and the different functions
of your muscles and the brain

00:04:19.519 --> 00:04:20.537
and all the things you body does,

00:04:20.537 --> 00:04:23.323
and some of it is just producing heat.

00:04:23.323 --> 00:04:24.763
Sometimes as a byproduct of that movement

00:04:24.763 --> 00:04:27.781
and sometimes, frankly, just
for the sake of producing heat.

00:04:27.781 --> 00:04:31.264
So, 500 calories you see on a food label,

00:04:31.264 --> 00:04:32.936
that's really 500 kilocalories,

00:04:32.936 --> 00:04:35.249
and that's enough energy

00:04:35.249 --> 00:04:38.676
to raise 500,000 grams of water,

00:04:38.676 --> 00:04:41.927
remember 500 kilograms,
500,000 grams of water,

00:04:41.927 --> 00:04:43.343
one degree celsius,

00:04:43.343 --> 00:04:47.522
or 50,000 grams of water
10 degrees celsius.

00:04:47.522 --> 00:04:50.541
But anyway, water has a
special name, it's calorie.

00:04:50.541 --> 00:04:51.795
It's neat to be able to connect it to,

00:04:51.795 --> 00:04:53.211
well, what we're eating and to think

00:04:53.211 --> 00:04:54.790
about what a calorie actually means,

00:04:54.790 --> 00:04:56.346
or what kilocalorie actually means.

00:04:56.346 --> 00:04:58.807
But this notion that water

00:04:58.807 --> 00:05:01.430
has a higher relative specific heat

00:05:01.430 --> 00:05:04.031
to, say, things like land,
actually has huge impacts

00:05:04.031 --> 00:05:04.937
on our climate.

00:05:04.937 --> 00:05:06.980
It's actually one of the
reasons why it's often nice

00:05:06.980 --> 00:05:08.953
to live near the coast.

00:05:08.953 --> 00:05:13.110
Because, let me draw,
let me draw a coastline.

00:05:13.110 --> 00:05:14.433
Right over here.

00:05:15.213 --> 00:05:17.698
This is, actually I'll draw it from,

00:05:17.698 --> 00:05:19.533
I'll draw it from above.

00:05:19.533 --> 00:05:20.810
So that's the coastline.

00:05:20.810 --> 00:05:22.319
This is land.

00:05:22.319 --> 00:05:23.619
Let's just say it's made up of sand,

00:05:23.619 --> 00:05:25.779
for the sake of argument,
and other things.

00:05:25.779 --> 00:05:27.288
This is water.

00:05:27.638 --> 00:05:28.449
Let's think about it,

00:05:28.449 --> 00:05:30.042
first let's think about it in the summer.

00:05:30.042 --> 00:05:33.548
Let's think about in the
summer, when it is hot.

00:05:33.548 --> 00:05:36.088
Think about just a sunny day.

00:05:36.372 --> 00:05:39.158
So in the summer, when things are hot,

00:05:39.158 --> 00:05:42.316
so you have the sun, you
have the sun right over here

00:05:42.316 --> 00:05:44.870
and it's radiating energy and
obviously the area also has,

00:05:44.870 --> 00:05:49.625
is also warming up the things
that it comes in touch with.

00:05:50.095 --> 00:05:52.881
But you're having, at
least at the coastline,

00:05:52.881 --> 00:05:55.597
the air is roughly the
same temperature over both

00:05:55.597 --> 00:05:58.175
and, although there
will be some variation,

00:05:58.175 --> 00:05:59.963
and they're getting the
same amount of sunlight.

00:05:59.963 --> 00:06:02.888
But since water has a
higher specific heat,

00:06:02.888 --> 00:06:07.346
that heat is going to warm up water less.

00:06:07.346 --> 00:06:09.273
So this is going to get less hot.

00:06:09.273 --> 00:06:10.620
Let me write it over here.

00:06:10.620 --> 00:06:13.122
This is going to get less hot.

00:06:13.755 --> 00:06:14.883
Less hot.

00:06:14.883 --> 00:06:17.270
And the land is going to get more hot.

00:06:17.647 --> 00:06:19.057
More hot.

00:06:19.643 --> 00:06:20.665
More hot.

00:06:20.665 --> 00:06:22.105
And that's why, when
you're on the coastline,

00:06:22.105 --> 00:06:24.450
the air is also affected
by what's in touch with it,

00:06:24.450 --> 00:06:26.307
it's gonna be in tough
with this less hot water,

00:06:26.307 --> 00:06:29.070
and so as the air, especially
if it's coming from the ocean,

00:06:29.070 --> 00:06:30.928
if the air is going in this direction,

00:06:30.928 --> 00:06:32.576
then if you're at the
coast, you're gonna get

00:06:32.576 --> 00:06:33.853
probably a cooler breeze

00:06:33.853 --> 00:06:35.795
than if you're more inland over here.

00:06:35.795 --> 00:06:37.281
If you're more inland over here,

00:06:37.281 --> 00:06:40.524
the air is going to be hotter.

00:06:40.524 --> 00:06:43.774
So this is going to be
hotter air if you're inland.

00:06:43.774 --> 00:06:45.771
And it's less hot air if
you're at the coastline

00:06:45.771 --> 00:06:48.023
because the air is being
cooled down to some degree,

00:06:48.023 --> 00:06:50.926
it's not being warmed
up as much by the water.

00:06:50.926 --> 00:06:52.458
Now you have the opposite
effect if you think

00:06:52.458 --> 00:06:54.083
about the coldest times of the year.

00:06:54.083 --> 00:06:56.452
If you think about the middle
of the night in the winter.

00:06:56.452 --> 00:06:57.956
So let me draw that.

00:06:59.702 --> 00:07:02.349
If you think about
nighttime in the winter,

00:07:02.349 --> 00:07:04.805
when everything is cooling down,

00:07:05.020 --> 00:07:06.390
when everything is cooling down

00:07:06.390 --> 00:07:07.899
once you have your coastline.

00:07:07.899 --> 00:07:11.080
Well now, both the land over here

00:07:11.890 --> 00:07:14.163
and the water, they're
going to be radiating heat

00:07:14.977 --> 00:07:17.081
and the water is going
to be radiating heat,

00:07:17.081 --> 00:07:18.513
there's no other sources of heat,

00:07:18.513 --> 00:07:20.765
there's radiating heat into the air.

00:07:20.765 --> 00:07:24.782
But if they radiate roughly
the same amount of heat,

00:07:24.782 --> 00:07:27.939
the land is going to drop in
temperature much much more.

00:07:27.939 --> 00:07:29.867
So it's going to get colder here.

00:07:29.867 --> 00:07:31.817
So the land is going to get colder

00:07:31.817 --> 00:07:34.209
and the water is going to get less cold.

00:07:35.029 --> 00:07:36.852
Because it works in both directions.

00:07:36.852 --> 00:07:38.222
More energy goes in the water,

00:07:38.222 --> 00:07:40.149
the temperature changes
less, and it can also radiate

00:07:40.149 --> 00:07:43.864
the same amount of heat,
but also lose less,

00:07:44.464 --> 00:07:46.961
it would also lose less temperature.

00:07:46.967 --> 00:07:49.768
So in the winter, in really
cold times of the year,

00:07:49.768 --> 00:07:51.416
well the air above the water,

00:07:51.416 --> 00:07:52.484
when it comes in touch with the water,

00:07:52.484 --> 00:07:54.829
is going to be less cold
than the air above the land

00:07:54.829 --> 00:07:56.733
because the water is
less cold than the land.

00:07:56.733 --> 00:07:58.451
And so it's nice to live near the water.

00:07:58.451 --> 00:08:00.355
It's going to be less
cold in the coastal areas

00:08:00.355 --> 00:08:02.608
than it would be if you're further inland.

00:08:02.608 --> 00:08:04.604
And this phenomenon,
this is frankly anywhere

00:08:04.604 --> 00:08:05.657
where you might see water,

00:08:05.657 --> 00:08:07.513
but it's very pronounced where I live.

00:08:07.513 --> 00:08:09.071
I live in the San Fransisco Bay area.

00:08:09.071 --> 00:08:13.157
And if you live, you literally
have the Pacific Ocean.

00:08:13.157 --> 00:08:14.388
Let me draw that.

00:08:14.388 --> 00:08:18.590
You have the Pacific Ocean here.

00:08:19.480 --> 00:08:22.784
You have the ocean right over here.

00:08:22.784 --> 00:08:27.381
And you have the San Fransisco Bay

00:08:27.381 --> 00:08:29.796
that looks something like that.

00:08:29.796 --> 00:08:32.141
You have your Golden Gate
Bridge right over here,

00:08:32.141 --> 00:08:33.650
for anyone who is curious.

00:08:33.650 --> 00:08:35.369
This is San Fransisco right up here.

00:08:35.369 --> 00:08:37.900
I actually live right about there.

00:08:37.900 --> 00:08:40.523
And you see it, if you
hang out in the summer,

00:08:40.523 --> 00:08:42.799
in the middle of the day in the coastline,

00:08:42.799 --> 00:08:46.700
it could be maybe 10 degrees,
even 20 degrees cooler

00:08:46.700 --> 00:08:49.950
than if you are well inland over here.

00:08:49.950 --> 00:08:52.853
So it has a very profound
impact on weather patterns.

00:08:52.853 --> 00:08:55.523
So the last thing you
might be wondering is,

00:08:55.523 --> 00:08:59.284
well why does water have
such a high specific heat?

00:08:59.284 --> 00:09:01.513
Well that goes back to
our good old friend,

00:09:01.513 --> 00:09:03.348
the hydrogen bond.

00:09:03.348 --> 00:09:05.669
Because, if we're talking
about a solid substance,

00:09:06.279 --> 00:09:07.936
if we're talking about a solid substance,

00:09:07.936 --> 00:09:10.690
and I'll just draw a
generic solid substance.

00:09:10.690 --> 00:09:13.398
So solid substance right over here.

00:09:13.398 --> 00:09:14.202
I don't know what this is,

00:09:14.202 --> 00:09:16.478
let's say it's some type of structure

00:09:16.478 --> 00:09:18.846
that looks something like this.

00:09:18.846 --> 00:09:20.471
As it gets energy,

00:09:20.471 --> 00:09:24.720
as it gets heat energy, the
heat energy just increases

00:09:24.720 --> 00:09:28.157
the kinetic energy of
the actual particles.

00:09:28.157 --> 00:09:30.270
It actually just makes them vibrate more.

00:09:30.270 --> 00:09:32.151
Makes them vibrate in place more.

00:09:32.151 --> 00:09:33.637
And that's actually what temperature is.

00:09:33.637 --> 00:09:34.983
It's really average kinetic energy.

00:09:34.983 --> 00:09:36.562
When you touch something
and go ooh, that's hot,

00:09:36.562 --> 00:09:38.327
it's really because those
things are just vibrating

00:09:38.327 --> 00:09:41.136
super super super super fast.

00:09:41.136 --> 00:09:42.924
So it's gonna make these
things vibrate more.

00:09:42.924 --> 00:09:44.248
Almost in place, especially
if we're thinking

00:09:44.248 --> 00:09:46.221
about something that is a solid.

00:09:46.221 --> 00:09:49.820
While in the case of water,
sure, when you get more energy,

00:09:49.820 --> 00:09:52.606
it's gonna make the water
molecules move around faster,

00:09:52.606 --> 00:09:54.743
vibrate more, have more kinetic energy.

00:09:54.743 --> 00:09:57.065
But in order to have more kinetic energy,

00:09:57.065 --> 00:09:59.920
they're gonna have to
overcome this kind of creation

00:09:59.920 --> 00:10:03.055
and breaking up of the hydrogen bonds.

00:10:03.055 --> 00:10:05.122
You can almost imagine the
friction of a hydrogen bond.

00:10:05.122 --> 00:10:08.117
You can imagine if this
water molecule wants to move

00:10:08.117 --> 00:10:10.439
in this direction, it has
to break this hydrogen bond,

00:10:10.439 --> 00:10:11.669
it's gonna form another hydrogen bond,

00:10:11.669 --> 00:10:12.691
it's gotta break that.

00:10:12.691 --> 00:10:15.700
So it needs energy to keep breaking

00:10:15.700 --> 00:10:17.645
those hydrogen bonds,
overcoming the friction

00:10:17.645 --> 00:10:18.783
of those hydrogen bonds

00:10:18.783 --> 00:10:20.779
and I'll use the friction in quotes

00:10:20.779 --> 00:10:23.194
'cause it's, well actually all friction

00:10:23.194 --> 00:10:26.561
is actually some type of
atomic force that's occurring

00:10:26.561 --> 00:10:28.674
at a microscopic level.

00:10:28.674 --> 00:10:30.090
But it's having to overcome that.

00:10:30.090 --> 00:10:31.545
And so some of this heat energy

00:10:31.545 --> 00:10:33.309
is actually used to overcome that

00:10:33.309 --> 00:10:35.724
as opposed to increasing
the actual kinetic energy

00:10:35.724 --> 00:10:38.580
of the individual molecules,
or making them vibrate

00:10:38.580 --> 00:10:40.577
or whatever to actually
increase their temperature.

00:10:40.577 --> 00:10:43.526
And this is why water is
able to store more heat

00:10:43.526 --> 00:10:47.189
and why it has a higher specific heat.


Water as a solvent

WEBVTT
Kind: captions
Language: en

00:00:00.306 --> 00:00:01.850
- [Voiceover] We've already
talked about the notion

00:00:01.850 --> 00:00:04.021
that a water molecule has polarity to it.

00:00:04.021 --> 00:00:06.227
One end has a partially negative charge,

00:00:06.227 --> 00:00:09.222
and the other end has
partially positive charges.

00:00:09.222 --> 00:00:11.683
And we've talked about how
this leads to hydrogen bonds,

00:00:11.683 --> 00:00:13.099
and we alluded to the fact

00:00:13.099 --> 00:00:14.701
that maybe these hydrogen bonds

00:00:14.701 --> 00:00:16.942
give us all sorts of
neat properties of water.

00:00:16.942 --> 00:00:18.207
And what I want to talk
about in this video

00:00:18.207 --> 00:00:21.086
is one of those very important properties,

00:00:21.086 --> 00:00:25.614
and that's water's ability to be a solvent

00:00:25.614 --> 00:00:29.081
Water's ability to be a solvent.

00:00:29.081 --> 00:00:31.542
And this means that it's
easy for certain things

00:00:31.542 --> 00:00:33.748
to be dissolved inside of water.

00:00:33.748 --> 00:00:34.769
And that's super important,

00:00:34.769 --> 00:00:36.650
because that's how a lot
of the chemistry occurs,

00:00:36.650 --> 00:00:38.380
by things getting dissolved in water

00:00:38.380 --> 00:00:41.363
and then interacting and
bumping with other things.

00:00:41.363 --> 00:00:43.279
And this is actually what's
happening inside of cells,

00:00:43.279 --> 00:00:44.440
in the cytoplasm.

00:00:44.440 --> 00:00:46.704
The cytoplasm, which is mostly water,

00:00:46.704 --> 00:00:49.269
is a solvent which allows
a bunch of interactions

00:00:49.269 --> 00:00:51.765
to happen between different
types of molecules.

00:00:51.765 --> 00:00:55.283
But let's think about why
water is a good solvent,

00:00:55.283 --> 00:00:58.498
and what types of things
it can dissolve easily

00:00:58.498 --> 00:00:59.961
and what types of things it might not

00:00:59.961 --> 00:01:02.469
be able to dissolve so easily.

00:01:02.469 --> 00:01:05.847
So the key feature that
makes water a good solvent,

00:01:05.847 --> 00:01:08.900
or at least a good solvent for
a large class of molecules,

00:01:08.900 --> 00:01:12.301
is its polarity.

00:01:12.301 --> 00:01:15.842
If I were to take some sodium chloride,

00:01:15.842 --> 00:01:18.036
often known as table salt,

00:01:18.036 --> 00:01:19.116
so let me...

00:01:19.116 --> 00:01:24.116
So if I were to take sodium
NaCl, sodium chloride.

00:01:24.282 --> 00:01:26.557
Sodium chloride, the sodium and chloride

00:01:26.557 --> 00:01:28.461
are attracted by ionic bonds.

00:01:28.461 --> 00:01:30.945
The sodium right over here
has a positive charge,

00:01:30.945 --> 00:01:33.615
it has an electron stripped from it,

00:01:33.615 --> 00:01:35.902
and the chloride has a--

00:01:35.902 --> 00:01:39.230
let me write that in a different color.

00:01:39.230 --> 00:01:41.053
So the sodium has a positive charge,

00:01:41.053 --> 00:01:42.846
because it has an
electron stripped from it,

00:01:42.846 --> 00:01:45.452
and the chloride, it is an anion,

00:01:45.452 --> 00:01:48.224
it has a negative, it is
a negatively charged ion,

00:01:48.224 --> 00:01:51.428
because it gains an extra electron.

00:01:51.428 --> 00:01:52.624
But they are attracted to each other.

00:01:52.624 --> 00:01:54.980
This has a positive charge,
this has a negative charge.

00:01:54.980 --> 00:01:56.919
This is called an ionic bond.

00:01:56.919 --> 00:01:59.241
But if you put sodium chloride in water,

00:01:59.241 --> 00:02:00.564
something very interesting happens.

00:02:00.564 --> 00:02:01.888
This is something that
we've all experienced.

00:02:01.888 --> 00:02:04.964
Take some table salt and put it in water

00:02:04.964 --> 00:02:06.067
and see what happens.

00:02:06.067 --> 00:02:07.739
It will dissolve.

00:02:07.739 --> 00:02:09.201
And why does it dissolve?

00:02:09.201 --> 00:02:11.808
Well, let's draw it out.

00:02:12.301 --> 00:02:14.805
So this is the sodium right over here.

00:02:14.805 --> 00:02:16.324
So that's the sodium.

00:02:16.324 --> 00:02:18.553
It has a positive charge.

00:02:18.553 --> 00:02:20.991
It has a positive charge.

00:02:20.991 --> 00:02:25.402
And then this is the
chloride right over here.

00:02:25.402 --> 00:02:27.225
It has a negative charge.

00:02:27.225 --> 00:02:30.882
What's gonna happen if you
put it inside of the water?

00:02:30.882 --> 00:02:33.041
Let me do that negative
charge in the green.

00:02:33.041 --> 00:02:36.570
What's gonna happen when
you put it inside of water.

00:02:36.570 --> 00:02:37.987
Well, you can imagine.

00:02:37.987 --> 00:02:39.948
The negative ends of the water molecules

00:02:39.948 --> 00:02:43.663
are going to be attracted
to the sodium ion.

00:02:43.663 --> 00:02:46.380
So it's going to look something like this.

00:02:46.380 --> 00:02:48.760
So you have the oxygen,

00:02:48.760 --> 00:02:53.264
oxygen, oxygen, oxygen, oxygen,

00:02:53.264 --> 00:02:54.843
I'm clearly not drawing things to scale,

00:02:54.843 --> 00:02:56.468
but this'll just give you the idea.

00:02:56.468 --> 00:02:58.662
This end of the water molecule

00:02:58.662 --> 00:03:01.460
all has a partially negative charge.

00:03:01.460 --> 00:03:02.923
Partially negative charge.

00:03:02.923 --> 00:03:06.545
So it's going to be attracted
to the positive sodium ion.

00:03:06.545 --> 00:03:09.041
And then the hydrogen ends,

00:03:09.041 --> 00:03:10.469
the hydrogen ends,

00:03:10.469 --> 00:03:12.686
are going to have a
partial positive charge,

00:03:12.686 --> 00:03:14.601
and then they're going to be repelled.

00:03:14.601 --> 00:03:19.601
They are going to be repelled
from the positive sodium ion.

00:03:20.355 --> 00:03:22.760
So it's gonna look something like this.

00:03:23.195 --> 00:03:26.039
And it's gonna look something like this.

00:03:26.039 --> 00:03:29.087
And you're gonna have
partial positive charge

00:03:29.087 --> 00:03:31.050
on the outside.

00:03:31.050 --> 00:03:33.755
Partial positive charge on the outside.

00:03:33.755 --> 00:03:35.636
And now these hydrogens over here,

00:03:35.636 --> 00:03:37.249
this will just interact with water

00:03:37.249 --> 00:03:38.991
the way that it would typically,

00:03:38.991 --> 00:03:40.407
with the hydrogen bonding,

00:03:40.407 --> 00:03:42.950
the molecules just
flowing past each other.

00:03:42.950 --> 00:03:46.072
So the fact that the sodium ion here,

00:03:46.072 --> 00:03:48.626
it's an ion, it has charge.

00:03:48.626 --> 00:03:51.970
It is able to dissolve
in the water very easily,

00:03:51.970 --> 00:03:54.953
because it is attracted to
the partially negative ends

00:03:54.953 --> 00:03:56.428
of the water molecule.

00:03:56.428 --> 00:03:57.867
Now, a similar thing is going to happen

00:03:57.867 --> 00:04:00.653
with the chloride ion.

00:04:00.653 --> 00:04:03.149
And we call a negative ion an anion.

00:04:03.149 --> 00:04:05.192
So over here, over here,

00:04:05.192 --> 00:04:07.212
and actually let me get some,

00:04:07.212 --> 00:04:08.965
let me move it over a little bit

00:04:08.965 --> 00:04:10.776
so that I have some space.

00:04:10.776 --> 00:04:13.616
So the chloride anion,

00:04:13.616 --> 00:04:16.851
let me move it over a little bit.

00:04:16.851 --> 00:04:21.310
So right, or maybe I'll move it over here.

00:04:22.256 --> 00:04:24.539
So the chloride,

00:04:24.539 --> 00:04:26.094
the chloride anion,

00:04:26.094 --> 00:04:28.834
let me see, I'm having trouble
with my selection tool.

00:04:28.834 --> 00:04:30.993
Alright. So there we go.

00:04:30.993 --> 00:04:33.257
The chloride anion has a negative charge

00:04:33.257 --> 00:04:36.310
that's going to be attracted
to the positive end

00:04:36.310 --> 00:04:37.912
of the water molecules.

00:04:37.912 --> 00:04:40.199
So you could imagine something like this.

00:04:40.199 --> 00:04:42.997
So the hydrogen ends, the hydrogen ends,

00:04:42.997 --> 00:04:44.518
are going to be attracted to it,

00:04:44.518 --> 00:04:47.060
they have a partially positive charge.

00:04:47.060 --> 00:04:49.649
They have a partially positive charge.

00:04:49.649 --> 00:04:51.448
And of course you have the oxygen end

00:04:51.448 --> 00:04:53.735
that has a partially negative charge.

00:04:53.735 --> 00:04:55.593
It has a partially negative charge.

00:04:55.593 --> 00:04:58.077
And I could draw more of these.

00:04:58.077 --> 00:04:59.830
Hydrogen, hydrogen,

00:04:59.830 --> 00:05:00.910
attracted there,

00:05:00.910 --> 00:05:03.057
you have the oxygen over,

00:05:03.057 --> 00:05:06.494
let me do that, I wanna
keep my colors consistent.

00:05:06.494 --> 00:05:08.374
The oxygen right over there,

00:05:08.374 --> 00:05:09.593
we have the hydrogen,

00:05:09.593 --> 00:05:11.648
once again this isn't drawn to scale.

00:05:11.648 --> 00:05:15.607
Hydrogen, it is bonded to the oxygen.

00:05:15.607 --> 00:05:17.708
And so once again, you can form this,

00:05:17.708 --> 00:05:21.017
so you could almost imagine
this shell of water molecules

00:05:21.017 --> 00:05:22.375
is going to be attracted to it,

00:05:22.375 --> 00:05:25.707
it's going to be attracted,
or I guess you could say

00:05:25.707 --> 00:05:28.307
the partially positive end,

00:05:28.307 --> 00:05:30.687
which is where the hydrogen atoms are,

00:05:30.687 --> 00:05:33.392
is what's going to be
attracted to this negative ion.

00:05:33.392 --> 00:05:35.632
So this is partial positive over here.

00:05:35.632 --> 00:05:37.014
And then on the partially negative side,

00:05:37.014 --> 00:05:38.732
outside of this shell,

00:05:38.732 --> 00:05:40.311
you can imagine it's just
gonna interact with the water

00:05:40.311 --> 00:05:42.110
just the way any water molecule would,

00:05:42.110 --> 00:05:44.885
and so it's gonna be
able to flow very easily.

00:05:44.885 --> 00:05:47.032
So you probably see
something interesting here.

00:05:47.032 --> 00:05:48.425
If something has charge,

00:05:48.425 --> 00:05:50.387
if it's an ion,

00:05:50.387 --> 00:05:52.407
or if something has some polarity,

00:05:52.407 --> 00:05:55.913
it's very easy to dissolve
it inside of water.

00:05:55.913 --> 00:05:59.233
And in this case, and just to
have some terminology here,

00:05:59.233 --> 00:06:02.403
in this case, water is the,

00:06:02.403 --> 00:06:05.073
water is the solvent,

00:06:05.073 --> 00:06:07.487
so water is the solvent.

00:06:07.487 --> 00:06:09.763
So the solvent is water.

00:06:09.763 --> 00:06:12.352
And the thing that's being
dissolved in the water,

00:06:12.352 --> 00:06:14.386
we call that a solute.

00:06:14.937 --> 00:06:17.920
So we call this the solute.

00:06:17.920 --> 00:06:19.383
So the sodium chloride.

00:06:19.383 --> 00:06:23.260
That is, you could use
sodium chloride as a solute,

00:06:23.260 --> 00:06:26.557
or you could say that the
sodium ions are a solute

00:06:26.557 --> 00:06:29.715
and so are the chloride ions.

00:06:29.715 --> 00:06:34.715
That is also considered to be the solute.

00:06:34.916 --> 00:06:36.912
And so you say, well what
kind of things dissolve well?

00:06:36.912 --> 00:06:39.292
Well, things that that have
charge or that are polar.

00:06:39.292 --> 00:06:40.813
And things that are charged and polar

00:06:40.813 --> 00:06:42.520
and tend to dissolve well in water,

00:06:42.520 --> 00:06:44.191
there's another word we use for them.

00:06:44.191 --> 00:06:46.780
We say that they are hydrophilic.

00:06:46.780 --> 00:06:51.780
So we could say that this
right over here is hydrophilic.

00:06:52.603 --> 00:06:54.136
And if you look at the word root,

00:06:54.136 --> 00:06:56.748
hydro is referring to water.

00:06:56.748 --> 00:07:00.068
So hydro is referring to water.

00:07:00.068 --> 00:07:01.496
And philic means loving.

00:07:01.496 --> 00:07:04.236
So this literally means water loving.

00:07:04.236 --> 00:07:07.010
Water loving.

00:07:07.010 --> 00:07:08.717
Hydrophilic.

00:07:08.717 --> 00:07:09.994
And so you might be asking, okay,

00:07:09.994 --> 00:07:10.969
everything we've talked about,

00:07:10.969 --> 00:07:12.408
you know, we've seen water molecules,

00:07:12.408 --> 00:07:15.287
that's polar, we're
looking at charged ions,

00:07:15.287 --> 00:07:16.309
okay we could get that,

00:07:16.309 --> 00:07:18.050
we can get why they'd be hydrophilic,

00:07:18.050 --> 00:07:20.511
they can incorporate
themselves well into the water,

00:07:20.511 --> 00:07:21.626
but what are examples of things

00:07:21.626 --> 00:07:24.551
that would not incorporate
themselves well in water?

00:07:24.551 --> 00:07:26.490
Well, in general, things
that don't have charge,

00:07:26.490 --> 00:07:29.009
or that aren't polar, aren't
going to be able to dissolve

00:07:29.009 --> 00:07:30.634
in water all that well.

00:07:30.634 --> 00:07:33.072
And a good example is hydrocarbons.

00:07:33.072 --> 00:07:34.674
So if you took some hexane.

00:07:34.674 --> 00:07:38.106
And hexane is a major
constituent of car gasoline.

00:07:38.106 --> 00:07:42.007
So hexane, hex the
prefix means six carbons.

00:07:42.007 --> 00:07:43.378
So let's see, one,

00:07:43.378 --> 00:07:45.588
let me do this in another color.

00:07:45.588 --> 00:07:50.429
So we have one, two, three,

00:07:50.429 --> 00:07:54.968
four, five, six carbons.

00:07:54.968 --> 00:07:57.488
So one two three four five six carbons.

00:07:57.488 --> 00:08:01.667
And then all the other
bonds are with hydrogens.

00:08:01.667 --> 00:08:05.486
So let me draw this as well as I can.

00:08:05.486 --> 00:08:09.504
Carbon, at least typically,
forms four bonds.

00:08:09.504 --> 00:08:14.504
So hydrogen, hydrogen, hydrogen, hydrogen,

00:08:14.631 --> 00:08:18.269
hydrogen, hydrogen, hydrogen.

00:08:18.269 --> 00:08:20.974
This right over here is hexane.

00:08:20.974 --> 00:08:23.354
This thing has no polarity to it.

00:08:23.354 --> 00:08:24.805
It doesn't form hydrogen bonds,

00:08:24.805 --> 00:08:26.244
it doesn't have any polarity.

00:08:26.244 --> 00:08:28.009
And so if you were to take hexane

00:08:28.009 --> 00:08:29.449
and throw it into water,

00:08:29.449 --> 00:08:31.248
it's not going to dissolve that well.

00:08:31.248 --> 00:08:33.071
It's actually going to kind bead up.

00:08:33.071 --> 00:08:34.649
And you would see that
if you actually threw

00:08:34.649 --> 00:08:36.669
some gasoline inside of water.

00:08:36.669 --> 00:08:40.651
So things like hexane we
would call hydrophobic.

00:08:40.651 --> 00:08:42.485
Hydrophobic.

00:08:42.485 --> 00:08:47.222
So this right over here is hydrophobic.

00:08:47.222 --> 00:08:48.011
Hydrophobic.

00:08:48.011 --> 00:08:50.368
It'll literally ball up
to avoid getting in touch,

00:08:50.368 --> 00:08:52.109
to minimize its contact with water.

00:08:52.109 --> 00:08:53.885
Because the water is attracted to itself,

00:08:53.885 --> 00:08:56.509
and it is not so attracted to
this stuff right over here.

00:08:56.509 --> 00:08:57.682
And hydrophobic?

00:08:57.682 --> 00:08:59.423
You still have hydro, meaning water,

00:08:59.423 --> 00:09:01.745
and then phobic, it means fearing.

00:09:01.745 --> 00:09:03.509
So this right over here is water fearing.

00:09:03.509 --> 00:09:07.120
That's why it's hard to mix
things like water and oil

00:09:07.120 --> 00:09:09.738
or gasoline and water.


Liquid water denser than solid water (ice)

WEBVTT
Kind: captions
Language: en

00:00:00.261 --> 00:00:02.490
- [Voiceover] If you
look at most substances,

00:00:02.490 --> 00:00:05.985
so this is most things, right over here.

00:00:05.985 --> 00:00:08.353
As we go from a liquid state

00:00:08.353 --> 00:00:10.756
where things are literally fluid,

00:00:10.756 --> 00:00:12.819
the molecules are moving past each other,

00:00:12.819 --> 00:00:16.778
to a solid state, where things
are rigid or more rigid,

00:00:16.778 --> 00:00:19.379
you typically have something
getting more dense.

00:00:19.379 --> 00:00:22.583
So the liquid state would be less dense.

00:00:22.583 --> 00:00:24.023
Less dense.

00:00:24.023 --> 00:00:27.808
And the solid state would be more dense.

00:00:27.808 --> 00:00:29.317
Would be more dense.

00:00:29.317 --> 00:00:31.546
Let's think about what
would happen if water

00:00:31.546 --> 00:00:34.193
were like most things here.

00:00:34.193 --> 00:00:36.632
So imagine a body of water.

00:00:37.743 --> 00:00:39.284
So let's say that's the
land right over here,

00:00:39.284 --> 00:00:41.154
this is a cross section of a body of,

00:00:41.154 --> 00:00:44.625
I don't wanna draw brown
water, I wanna do blue water.

00:00:44.625 --> 00:00:46.959
So this is a cross
section of body of water,

00:00:46.959 --> 00:00:48.781
like say, we see in this picture here.

00:00:48.781 --> 00:00:50.787
Now let's say it is very cold.

00:00:50.787 --> 00:00:53.785
That the air is extremely cold.

00:00:53.785 --> 00:00:57.117
Let's say it's below the
freezing temperature of water.

00:00:57.117 --> 00:01:00.588
Well what would happen is the
water up here would freeze.

00:01:00.588 --> 00:01:02.794
And this is actually what does happen.

00:01:02.794 --> 00:01:04.524
Water at the surface would freeze,

00:01:04.524 --> 00:01:06.718
but if this ice were more dense,

00:01:06.718 --> 00:01:09.319
the solid water were more
dense than the liquid water,

00:01:09.319 --> 00:01:11.780
well then the ice would sink.

00:01:11.780 --> 00:01:15.069
The ice would sink and
collect at the bottom.

00:01:15.153 --> 00:01:18.926
The ice would collect at
the bottom right over here.

00:01:18.926 --> 00:01:21.527
And then the water over
here would freeze again.

00:01:21.527 --> 00:01:22.688
It would freeze again.

00:01:22.688 --> 00:01:24.789
But if that were more
dense, then it would sink

00:01:24.789 --> 00:01:26.217
and collect at the bottom.

00:01:26.217 --> 00:01:29.015
And you keep going with this
process on and on and on,

00:01:29.015 --> 00:01:31.221
and eventually the entire body of water,

00:01:31.221 --> 00:01:35.282
the entire lake would freeze solid.

00:01:35.282 --> 00:01:37.289
Would freeze...

00:01:37.289 --> 00:01:39.878
It would freeze solid.

00:01:39.878 --> 00:01:42.371
Now you can imagine this
wouldn't be that good

00:01:42.371 --> 00:01:45.088
for the animals that
are living in the water.

00:01:45.088 --> 00:01:47.085
If you imagine some fish in here.

00:01:47.085 --> 00:01:48.989
Those fish would then freeze.

00:01:48.989 --> 00:01:51.589
And most living things, there
are a few simple organisms

00:01:51.589 --> 00:01:53.493
that can survive being frozen.

00:01:53.493 --> 00:01:55.397
But most living things would just die.

00:01:55.397 --> 00:01:57.255
And so this would not
be a good environment

00:01:57.255 --> 00:02:02.094
for animals to live in, or for
even biology to take place.

00:02:02.094 --> 00:02:03.452
But what's neat about water,

00:02:03.452 --> 00:02:05.983
it does not follow this pattern.

00:02:05.983 --> 00:02:07.901
When we're talking about water,

00:02:08.360 --> 00:02:10.083
when we're talking about water,

00:02:10.083 --> 00:02:13.090
when we go to the liquid state,

00:02:13.090 --> 00:02:16.048
when we go from liquid water to solid ice,

00:02:16.048 --> 00:02:18.718
to solid ice, we actually get,

00:02:18.718 --> 00:02:20.692
we actually get less dense.

00:02:20.692 --> 00:02:23.316
So this right over here is less dense.

00:02:23.316 --> 00:02:26.691
This is why ice floats.

00:02:26.691 --> 00:02:29.628
This is more dense, more dense.

00:02:29.628 --> 00:02:30.917
And this is less dense.

00:02:30.917 --> 00:02:33.058
And to think about why
that is, it all goes back

00:02:33.058 --> 00:02:34.916
to the hydrogen bonding.

00:02:34.916 --> 00:02:37.061
So we've seen in previous videos.

00:02:37.061 --> 00:02:38.790
So, I'm gonna do it all in one color.

00:02:38.790 --> 00:02:41.786
Oxygen, hydrogen, hydrogen.

00:02:41.786 --> 00:02:43.454
Let's say this is the liquid
state that I'm drawing

00:02:43.454 --> 00:02:44.221
right over here.

00:02:44.221 --> 00:02:47.176
This is liquid water.

00:02:48.075 --> 00:02:49.318
Liquid water.

00:02:49.318 --> 00:02:52.359
So then you have oxygen,

00:02:52.359 --> 00:02:55.621
and you have oxygen and hydrogen

00:02:55.621 --> 00:02:56.655
and hydrogen.

00:02:56.655 --> 00:02:59.557
And you have oxygen and hydrogen

00:02:59.557 --> 00:03:00.660
and hydrogen.

00:03:00.660 --> 00:03:02.523
We've already talked multiple times

00:03:02.523 --> 00:03:03.858
about the fact that you have partial

00:03:03.858 --> 00:03:07.585
negative charges at the side
away from the hydrogens.

00:03:07.585 --> 00:03:09.094
Partial negative, partial negative

00:03:09.094 --> 00:03:11.126
because oxygen is so electro-negative.

00:03:11.126 --> 00:03:12.728
And you have partial positive charges

00:03:12.728 --> 00:03:14.121
on the hydrogen ends.

00:03:14.121 --> 00:03:17.383
Partial positive charges at the hydrogens

00:03:17.383 --> 00:03:19.740
and these partial negatives
and partial positives

00:03:19.740 --> 00:03:22.689
attract each other and this
is called hydrogen bonding.

00:03:22.689 --> 00:03:25.325
Now the liquid state,
you have enough energy.

00:03:25.325 --> 00:03:27.554
The temperature is just
really average kinetic energy

00:03:27.554 --> 00:03:29.551
that these molecules are
able to bounce around

00:03:29.551 --> 00:03:30.689
and flow past each other.

00:03:30.689 --> 00:03:32.523
These hydrogen bonds get broken

00:03:32.523 --> 00:03:34.520
and get reformed over and over again.

00:03:34.520 --> 00:03:35.994
These things flow past each other

00:03:35.994 --> 00:03:37.527
and also they have enough energy

00:03:37.527 --> 00:03:39.597
to kind of push even closer to each other

00:03:39.597 --> 00:03:41.184
than even the hydrogen
bonds would dictate.

00:03:41.184 --> 00:03:42.960
Sometimes they go closer,
sometimes they're further,

00:03:42.960 --> 00:03:44.621
sometimes they're pushing around.

00:03:44.621 --> 00:03:45.828
But as we get--

00:03:45.828 --> 00:03:50.828
As we get cooler, as we get
cooler and we lose heat,

00:03:50.855 --> 00:03:52.594
then they don't have the kinetic energy

00:03:52.594 --> 00:03:53.256
to kind of--

00:03:53.256 --> 00:03:55.392
They get closer and bump
up against each other

00:03:55.392 --> 00:03:58.619
and move right and flow
right past each other

00:03:58.619 --> 00:04:01.185
and they form a lattice structure

00:04:01.185 --> 00:04:03.606
where it will look more like this.

00:04:03.809 --> 00:04:06.375
Where it will look like oxygen,

00:04:06.375 --> 00:04:11.251
hydrogen, hydrogen, oxygen, hydrogen,

00:04:11.251 --> 00:04:15.384
hydrogen, oxygen, hydrogen, hydrogen.

00:04:15.384 --> 00:04:17.056
And so you actually have the molecules

00:04:17.056 --> 00:04:18.589
being further apart from each other

00:04:18.589 --> 00:04:19.784
because they don't have
the kinetic energy,

00:04:19.784 --> 00:04:22.548
once again, to keep breaking and reforming

00:04:22.548 --> 00:04:24.510
these hydrogen bonds, or even to kind of

00:04:24.510 --> 00:04:27.284
have the kinetic energy to
push up against each other.

00:04:27.284 --> 00:04:29.061
And so you form this lattice structure.

00:04:29.061 --> 00:04:30.756
You could even have another oxygen.

00:04:30.756 --> 00:04:32.985
And I'm obviously drawing
it in two dimensions,

00:04:32.985 --> 00:04:35.156
but ice, things in our universe,

00:04:35.156 --> 00:04:36.755
in our reality are three dimensions.

00:04:36.755 --> 00:04:39.911
But hopefully this gives you the

00:04:39.911 --> 00:04:41.504
big picture of it.

00:04:41.846 --> 00:04:43.692
Oxygen, hydrogen, hydrogen.

00:04:43.692 --> 00:04:45.956
And so you have these hydrogen bonds.

00:04:45.956 --> 00:04:47.825
I wanted to do those in white.

00:04:47.825 --> 00:04:49.021
These hydrogen bonds.

00:04:49.021 --> 00:04:50.484
And remember, these hydrogen bonds,

00:04:50.484 --> 00:04:52.190
they're still, it's still the case,

00:04:52.190 --> 00:04:54.117
electrons are still moving around,

00:04:54.117 --> 00:04:55.252
and so you still have a partial

00:04:55.252 --> 00:04:59.153
positive charge here and
partial negative charge there,

00:04:59.153 --> 00:05:00.953
but there's not enough
kinetic energy to push

00:05:00.953 --> 00:05:03.286
them close to each other
and flow past each other

00:05:03.286 --> 00:05:05.936
and so you have ice right over here.

00:05:06.151 --> 00:05:07.590
You have solid water.

00:05:07.590 --> 00:05:09.959
You have ice over here being less dense.

00:05:09.959 --> 00:05:12.153
And this is what keeps ice floating,

00:05:12.153 --> 00:05:13.593
this is what keeps icebergs floating,

00:05:13.593 --> 00:05:15.357
this is what keeps lakes like this

00:05:15.357 --> 00:05:16.460
from freezing solid.

00:05:16.460 --> 00:05:18.318
This is why the surface freezes,

00:05:18.318 --> 00:05:19.560
but you have water below it.

00:05:19.560 --> 00:05:21.648
In fact, that ice on the top protects

00:05:21.648 --> 00:05:23.121
the water below from...

00:05:23.121 --> 00:05:25.744
You can imagine, the ice, it protects it

00:05:25.744 --> 00:05:27.727
from getting even further frozen

00:05:27.727 --> 00:05:30.135
and so you have animals

00:05:30.135 --> 00:05:34.060
able to just hang out.

00:05:34.060 --> 00:05:35.581
Hang out down here and

00:05:35.581 --> 00:05:36.754
go through the winter and then

00:05:36.754 --> 00:05:38.751
everything will thaw once you get to

00:05:38.751 --> 00:05:41.439
the spring and the summer.