Hi. It's Mr. Andersen and this is chemistry essentials video 51. It's on calorimetry.
And like anything in chemistry a lot of this can go back to Antoine Lavoisier, that brilliant
chemist who started a lot of modern chemistry. And so calorimetry, if we just breakdown that
word, it means the measuring of heat. And the first calorimeter that was created by
Lavoisier was an ice calorimeter. And basically what you had was chamber that had ice on the
inside. And then an insulating chamber of ice around the outside of that. And then you
would put something inside the calorimeter, a candle for example. And what would happen
is it would generate heat as it's doing combustion. It would melt the ice around it. That ice
would turn into a liquid which you could measure. So you could measure the amount of energy
that's being released from the candle. He then put something living inside there. He
used a guinea pig to start. And what we found is that it occurred in the same way. In other
words that guinea pig is doing respiration which is a form of combustion. It's using
oxygen. It's releasing heat. And he showed that this is essentially the same kind of
a process. It requires oxygen, gives off carbon dioxide. And so what he was really looking
at is the energy given off by this system. And so a calorimeter is pretty simple. It
only has two parts. It has a heat bath around the outside. And that generally is made of
water. Because we know specifically how water changes over time. And then you're going to
have a chemical system that's placed inside of that. We need a thermometer inside that
heat bath so we can measure what's happening as we get changes of energy within it. And
so we could measure energy change from that chemical system. We could use this to measure
everything we described in the last video. The specific heat capacity. The enthalpy of
fusion and vaporization. And also the enthalpy of the reaction. And so let's start with water.
Imagine that we have a beaker of water. And we're adding energy to that. Remember we measure
how easily it's heated of cooled using a measurement called specific heat. And so if we breakdown
that equation, specific heat is equal to the quantity of heat transferred. And we're going
to measure that in joules. Divided by the grams of the substance. In other words how
much we have times the temperature change. And so let's give you a real example because
we know specifically what the specific heat is of water. It's 4.18 joules per gram kelvin.
And that's been well established. And it's going to be important that we understand that
as we start to do some calculations related calorimetry. And so imagine we have 250 milliliters
of water. Now what's interesting about water is we know immediately that we have 250 grams
of water. And we started at 18 degrees celsius. And so our mass is 250 grams. And our initial
temperature is going to be 18 degrees celsius. And let's say we heat it up. And so over time
it changes. And at the end it's 65 degrees celsius. And so our final, our T sub f is
going to be 65 degrees celsius. And so what we can do is figure out how much energy was
added to that water. And we're going to use specific heat to do it. Again specific heat
is equal to the quantity of heat transferred divided by the grams times the temperature
change. And so let's just start working down these values right here. Well we know specific
heat of water is going to be 4.18. We now know what the mass is. That's 250 grams. So
I'm just going to plug that in right here. We also know the temperature change. So we're
going from 18 to 65. And so we just take our final temperature minus our initial. And so
that's going to be 65 minus 18. That's going to be 47 degrees celsius. And do some simple
algebra. In other words I'm just going to multiply both sides by this. And so I'm going
to move it to there. And now I just simplify and I am going to find that the quantity of
heat that was transferred is 4.19 times ten to the fourth joules. And so where did that
energy come from? It came from the heating of that water. And so if we know how much
the water changes in its temperature and we know its mass, then we can figure out how
much energy is released. And that's really how a calorimeter works. All you have is you're
going to have a vessel where we're going to have that reaction or that heating or that
phase change occur. And then we're just going to have that sitting inside this heat bath.
We can measure the changes in temperature. And by measuring the changes in temperature,
how much energy is being released from that vessel or being consumed by that vessel. And
so if we heat up that material in there, let's say it's a chemical reaction. And we see changes
in the temperature, we know how much of that is coming from the reaction inside that vessel.
And so this is what an actual, this would be a bomb calorimeter. And what it's doing
is we're putting whatever we want to study inside this vessel. We're enclosing it inside
water. We have a really detailed thermometer on the inside. Lots of times they'll have
a stirrer so that we're moving that water around. And we can measure energy changes.
We could use that to measure specific heat capacity, enthalpy of fusion. That's when
we're going remember from a solid to a liquid. Or backwards. We could measure enthalpy of
vaporization as we're going from a liquid to a gas. Or we can just measure that enthalpy
of reaction. We could measure endothermic and exothermic reactions. And so that's the
role of a calorimeter. And so could you design or interpret the results of an experiment?
Again what we're looking at is changes in the water. And then we can work backwards
to figure out how are those changes coming from that vessel. And I hope that was helpful.