Hi. It's Mr. Andersen and this is chemistry essentials video 36. It's on temperature which
is the average kinetic energy of molecules. In this video right here I've got some water
that's at room temperature. And I'm going to add some warm water to it. And as we add
that we'll see the thermometer's going up. Why? Well we're speeding up the molecules.
And as we speed up those molecules they push more on each other and they're actually expanding
or they're moving away from each other. And we can use that in a thermometer to measure
the overall temperature. And so temperature remember is the average kinetic energy of
the molecules. And it's going to be a proportional relationship between the temperature and the
average kinetic energy using what's called the Kelvin cycle. And so in the Kelvin cycle
if there's no molecular motion, then there's no temperature. There's no Kelvin. And so
zero Kelvin is going to be absolute zero. No molecular motion. And so the distribution
of those molecules at different temperatures can be described using the Maxwell-Boltzmann
distribution. And so let's get to that. In this video what I've done is I've taken some
water. It's going to be 15 degrees. So I added some ice to it. It's kind of cold. And then
next to that I've got water that's at 65 degrees celsius. So it's going to be pretty hot. I'm
going to add a drop of food coloring to each. And we're going to watch what happens. So
you can see that the food coloring is spreading apart more at the 65 degrees. I speed up the
video right here so it's about four times. And so we can see that in the cold it's really
not moving apart very much at all. But in the warm we're seeing this huge amount of
movement of those molecules. And we can even see some some little convection currents going
on. And so why does that occur? Well everything is in motion. Everything is in molecular motion.
And so in this diagram right here we've go these particles. You could think of them representing
the water molecules. And then we have this particle, this large one which you could think
of represents one large food coloring molecule. And so if we run those in molecular motion
well find that they're all moving around really, really quickly. And as they do that they're
bumping on that particle. The faster they're bumping on the particle, the faster the particle
is going to move. And this path that it takes is random. We call it Brownian motion. But
if you look at all those particles right there you'll find that some are going slow and some
are going fast. And some are going really fast. But they're not all going the same speed.
And so when we're looking at temperature what we're looking at is the average speed of all
those particles. And so Lord Kelvin developed this scale. It's called the Kelvin scale.
And what it does is it measures the temperature, overall temperature. And so using this scale
zero Kelvin is going to be absolute zero, where there's no molecular motion. What you'll
find is if we're looking at celsius and the Kelvin, the marks are going to be the same.
Celsius was set up where zero is going to be freezing. One hundred is going to be boiling.
And so you can see how they kind of correspond in this right here. And so we could even calculate
absolute zero in the chemistry lab. How would you do that? If we take a balloon and we simply
measure its volume at different temperatures. So if we measure it at zero degrees. Put it
in a freezer for example. And then we warm it up and measure its volume. And then we
cool it down and measure its volume. What we could do is we could just extend that line.
And what we'll find is that that's going to have zero volume right at absolute zero. In
other words all the molecules are not moving at all so we've approached that absolute zero.
And so the Maxwell-Boltzmann distribution really talks to the overall motion of all
these different particles based on temperature. And so if we look at all of these particles
moving around or bouncing off one another, they're all going to have an average kinetic
energy. But they're each going to have individual kinetic energies or speeds of their own. And
so if we were to plot that out it would look something like this. So the average is going
to be right here. But there are going to be a lot of particles that have a slower than
average speed. And a lot that have a higher than average speed. And so if we were to increase
the temperature, what's that going to do to the Maxwell-Boltzmann distribution? It's going
to look more like that. In other words we're going to have more particles that are going
to have higher amounts of speed. Therefore a higher amount of temperature. And we'll
talk about heat and heat transfer in the next video. But for now, did you learn to relate
the temperature to the particle of the motions? The higher the temperature, the higher the
motions. I hope you did. And I hope that was helpful.