Hi. It's Mr. Andersen and this chemistry essentials video 47. It's on heat exchange. If I were
to say don't touch this iron right here in the middle, it's hot. What does that mean?
Well we know that it has a higher temperature. And therefore it has a higher amount of average
kinetic energy. And if you were to touch it a lot of that energy is going to be transferred
to your hand. And that's going to produce quite a bit of pain. And so if we ever have
a warmer body and a colder body, the warmer body is going to have more kinetic energy.
And again that energy is in the molecular motion or those molecules moving around. And
we're going to have more energy in that than in the colder body. And so a good way to represent
that, and I'll use this model over the next few videos is just using these little cubes
that represent the amount of energy. In this case that's going to be thermal energy. And
so if I were to put those two objects in contact with one another that energy is going to be
transferred. In other words energy is moving from that first object to that second object.
And we call that transfer heat. And so what we're really doing is transferring energy
as thermal energy or heat. Now heat if you were to look up heat on a periodic table you're
simply not going to find it there because it's not a substance. It's not a thing. It's
just the transfer of energy. And so a good way to think about that, and this should be
a sentence that should kind of roll of your tongue, energy is being transferred as heat.
That's really what's going on. And so when we're looking at energy being transferred
as heat, it's going to vary depending on the substance that we're dealing with. In other
words metals are going to transfer energy through heat more readily than things like
wood or brick. So let's look at this PHET simulation. So I've got iron. I've got brick.
And then I've got water. And so we can assume that we have the same amount of each of these.
And if I were to put the water on top of a heating device and the iron on top of a heating
device. And I were to just increase the amount of energy, what I'm going to see is an increase
in temperature. Well, what's really going on is that we're speeding up those molecules.
That's speeding up the molecules of the thermometer. It's spreading apart. Likewise when we cool
it down what we're doing is we're cooling down those molecules. Cooling down the molecules
of the thermometer and therefore it's going down. But we really don't see that energy
transfer as heat. And so now what we're going to do is we're going to click on the energy
symbols button. And now we're actually going to see that energy inside those molecules.
Now as I'm heating it up what's really happening is I'm adding energy. I'm adding energy to
that iron. Now you can see that some of it is being transferred out to the environment
through heat. Likewise when I cool it down what I'm doing is I'm actually transferring
that energy as heat into the ice cubes. So they have lower kinetic energy. What happens
if I take that iron and I just throw it into the water? You can see that since it's hotter
it's transferring some of that energy as heat as well to the surroundings until it eventually
reaches what we call equilibrium. And so if you ever have a warmer and a colder body,
that warmer body is going to have a higher amount of average kinetic energy. And remember
the Maxwell-Boltzmann distribution shows us how that works. If we were to look at it this
would be the cold body and this would be the warm body. Now in each of those bodies they're
going to have low energy particles and really high energy particles. But in the warmer body
that average kinetic energy is going to be greater. And so if we ever put them in contact
with another, there's going to be a lot of collisions between these molecules. And as
they collide they're transferring some of that kinetic energy. And so what we're really
doing is we're transferring energy from the warmer object to the colder object through
heat. Until they eventually reach what we call thermal equilibrium. In other words it's
the same average kinetic energy on both sides. And that picture I showed you of iron at the
beginning, eventually what's going to happen is all of that iron is going to have the same
amount of kinetic energy because we've transferred that energy out. Now it's not the same for
every substance. And so we use a term called specific heat capacity to measure that. And
so right here you could imagine we have a kilogram of gold, a kilogram of aluminum and
a kilogram of water. And let's say that they're all in a container. And so if you look at
it they're going to have different amounts of specific heat capacity. If we look at the
units that joules, which is a way that we measure energy per gram. And then kelvin,
or degree kelvin. And so if you have something that has low specific heat capacity that means
it's going to be changed. The amount of energy it has is going to change more readily than
something that has a higher specific heat capacity. So let's add a little bit of heat
to this. And watch what happens to the thermometers. And so the gold, the aluminum are heating
up more readily than the water. Now the energy is going to be the same. It's just that the
water has a higher specific heat capacity. And so it's able to absorb more energy before
it starts to change its temperature. And so did you learn to explain how heat exchange
is due to kinetic energy transfer due to molecular motions? If you did you learned what I wanted
you to and I hope that was helpful.