Hi. It's Mr. Andersen and this is chemistry essentials video 13 which is
on solids and liquids. And we have solids and liquids right here. Water in a both liquid
and a solid phase. And so when we're looking at solids and liquids, it's almost easier
to compare them. So we're going to use a Venn diagram. So we've got solids and liquids.
How are they alike? Well they're both made of matter. They both have a specific molar
volume. In other words, they're close enough where their molar volumes are going to be
about the same. And they're all going to be made of particles. So is all matter. But what's
different between liquids and solids is the intermolecular forces are going to be slightly
different between a solid and a liquid. And so if we look at solids they're going to be
highly ordered. And what that means is that their atoms are going to be locked into a
specific matrix. They can vibrate. In fact they have to vibrate over time. But as a result
they really are two different types. Amorphous and crystalline solids. If we're looking at
liquids, they're more disordered. And they can show what's called translation where they
can move around each other. And as a result, they're going to take the shape of whatever
container they're in. And then there are going to be properties based on these intermolecular
forces, like surface tension, viscosity, and volume and mixing that we talk about with
liquids that we don't have to talk about when we're talking about solids. And so how do
we look at these two and how they move from one into another? Well, we can look at a heating
curve. Or if you just turn that around, a cooling curve. And it's going to show us this
transition between the two. And so if we're looking at phases of matter, it's first best
to come up with some kind of a representation of what they look like. And so we're going
to use a simulation here from phet at colorado.edu. And so what we've got here is a bunch of water
in a solid phase. And so you can see that they're locked in position. And as we move
it to liquid, now they can translate. They can move around each other. Now this is not
a great model of a liquid. It should kind of flow down to the bottom. But at least we're
seeing what's going on at the particle phase. And then as we look at a gas, as we increase
the energy again, now they're moving all over the place. And we'll talk about gases in the
next video. And so what we're going to do is we're going to take some of that energy
away. We're going to take some of that heat away. And as we cool it down you can see hear
that we're measuring this in kelvin. As we cool it down it turns into a liquid. And now
it's into a solid. You can see even at a solid phase those still, we're seeing vibrations
within there. But as we approach absolute zero, all molecular motion is eventually going
to come to a stop when we reach that point. Okay. So when we're looking at solids, solids
are going to have a specific matrix. In other words all of the atom's molecules are going
to be put together in a specific shape. If it's amorphous, there's not going to be a
repeating pattern to this. And so this is amorphous right here. So you can see it's
made up of silicon and oxygen. But they're going to be put together in all different
shapes. And as a result we get what's called amorphous quartz. Or sometimes we call this
glassy quartz. And so it's going to be really brittle. Really easy to break. And so some
solids like rubber, for example, is going to be an amorphous solid. It doesn't mean
that it's not a solid, it's just not going to be as organized. And if we look at crystalline
structure, like that in this crystalline quartz, it's going to be the same atoms you can see.
But they're arranged in a repeating pattern. And now we get these beautiful crystals right
here. It's going to be harder. So a diamond for example is going to be something that
would be in a crystalline solid. As we move into liquids what they can show is something
called translation. So that means that, let's say we have these water molecules right here.
They're not locked in those positions. In other words they can translate about each
other. And as a result, liquids are going to take the shape of their container. Now
depending on the forces between those water molecules, we're going to have different properties.
One of the first ones is going to be viscosity. Viscosity is how easily a liquid is able to
flow. And so right here we've got a picture of pitch. Pitch is going to have really high
viscosity. That means it really is going to flow at a real slow rate. It's still going
to take the shape of the container you can see down here. And so something that would
have, for example, a real low viscosity might be water. It's going to easily flow. Alcohol
might be one that has a low viscosity. Another property is going to be surface tension. Surface
tension is going to be based on the intermolecular forces in a liquid. And so these different
molecules are going to be attracted to one another. And they're also going to be attracted
to one another at the surface. And so surface tension is going to be almost this layer of
chemical attraction over the surface of a liquid. And so a water strider like this is
able to float on top of that surface tension. If we were to break the surface tension, one
way to do that would be to add something like soap. It's going to break those intermolecular
forces, and trust me, that water strider is going to quickly sink to the bottom of the
lake. And then the last thing is called the volume of mixing. And this is best easily
understood if we use a demonstration. This is one that I use in my class. Imagine I were
to take some pure water, so we have distilled water. And I were to put it in a graduated
cylinder. And I were to be real precise and measure out exactly 250 milliliters of water.
I were then to take some ethyl alcohol, so ethanol. And I were to measure out exactly
250 milliliters of that as well. So let's say I'm very precise. I have 250 milliliters
of each, what do you think is going to happen if we combine those two amounts together in
another graduated cylinder? Well, when you do this, if you have a large enough amount,
you're not going to get 500 milliliters. And so that's weird. It seems like it disappeared.
But really what's going on is the water and the alcohol are able to fit within each other.
There's going to be room within there. And so that's based on those intermolecular forces
as well. If we were to combine water and water we would get 500 milliliters. But because
we have less attraction in those alcohol molecules, the water molecules can kind of get in there.
And so how do we look at then transition from solid to liquid and back again? We use something
called a heating curve. And so what we have down here is heat. So we're adding heat in
this direction. And then we've got the temperature on the side. And the heating curve I'm going
to show you is the heating curve for water. And so if we look at the heating curve for
water, it's going to look something like that. And so what happens below zero degrees celsius.
Well that's going to be a solid. It's going to be ice. What happens as we go above it?
It's going to turn into water. And then above 100 degrees celsius it's going to turn into
vapor. But why is it a flat line here? It seems like we're just losing energy. In other
words we're adding energy the whole way across. Why isn't the temperature increasing here?
Well what's happening is as we add energy to ice, as we reach that point what we have
right here is both ice and water. So we see a transition from a solid to a liquid. And
so that energy is going into that molecular motion of that solid becoming a liquid. Likewise,
where is the energy going here? It's going into the energy of those vapor molecules as
they jump off. And so as you heat water it's going to increase to around 100 degrees celsius
depending on your elevation. But at that point it eventually jumps into a vapor. And so we
could look at a heating curve to see the transition between both solid and liquid. And then our
next video, which is going to be on gases, if we flip this thing around then we've got
just a cooling curve. And then, did you learn this? That we can use a particulate model,
so we use that phet model to explain the difference between solid and liquid? Remember that big
point is when we move to a liquid they show translation. They can move around each other.
And I hope that was helpful.