Thermodynamical potentials: some hand-waving please

[jonas_nilsson]

Hello!

I am right now occupied with statistical physics, and of course the connections to thermodynamics are always there. We are especially verifying the old-school thermodynamical results. This leads to a lot of talking about thermodynamical potentials, but I feel that I and most of the students lack a "feeling" for them.

I would appreciate if some people could do some hand-waving and tell me what "feeling" they have developed for the thermodynamical potentials. What do they really describe? I'm sure it would help us out also with the theoretical stuff.


Jonas

 

[Crosson]

Suppose you wanted to conjure a rabbit in your hat. For one thing, you would have to assemble the molecules:

$$dU=\mu dN$$

But you would also have to do the work to make room for the rabbit:

$$dU = \mu dN + P dV$$ (Enthalpy)

And you can extract some energy from the surrounding air to help you:

$$dU = \mu dN + P dV - T ds$$ (Gibbs free energy)