Fundamentals of Thermodynamics
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Consider a gas expanding into a vacuum. The volume is changing and the question is, how is the internal energy changing with the change in volume.
Two absolutely critical properties of gas are its temperature and pressure. These determine the liquifying conditions of that gas. Joule and Thompson devised this experiment that shows how the temperature varies with the pressure.
Since we have looked at both Cv and Cp already, now is a good time to compare these heat capacities.
As we said in the introduction, there are two ways in which we can change the Internal energy.
The total energy of a system is called its internal energy.
We can break the universe into two parts, the system and the surroundings. The part we are looking at is the system, and everything else is the surroundings.