# Homework Help: Constant thermodynamic potentials examples

1. Jun 8, 2010

### dperkovic

1. The problem statement, all variables and given/known data

Specify at least two ( physical or chemical), real world, processes for each of this cases:

a) Internal energy is constant
b) Entalpy is constant
c) Gibbs free energy is constant
d) Helmholtz free energy is constant

2. Relevant equations

a) dU = TdS - pDV = 0
b) dH = TdS + VdP = 0
c) dG = dH - tdS = 0, or dG =vDp -SdT = 0 ???
d) dF = -(pdV + SdT ) = 0

3. The attempt at a solution

b) Joulle-Thompson effekt

...and this is all what I found...

Thanks for any help !

Last edited: Jun 8, 2010
2. Jun 8, 2010

### Mapes

It's not going to help you learn if people just provide the examples for you, so let's try this tack: what's the physical interpretation of $dS=0$? How about $dP=0$, and the others? Can you brainstorm some cases where these restrictions apply? For example, which state variables are constant when an exposed solid melts to form a liquid?

3. Jun 8, 2010

### dperkovic

Maybe it is true, but I think that knowing real world examples help me to better understand thermodynamics. Than, I can compare "mathematics" with real world.

4. Jun 8, 2010

### dperkovic

This stand for constant gibbs, am I right ?

5. Jun 8, 2010