# Enthalpy of ideal gas

1. May 14, 2010

### quantoshake11

Hello.
I'm having troubles solving the enthalpy for an ideal gas.
From the equation H=U+PV, i could find H substituting PV=NRT = U/c, but then i need the energy as a function of S and P, so i'd get H as a function of its proper variables (S and P)..
I can't find such an expression. It's just so easy to find the helmholtz and gibbs representation for ideal gases that i find it odd that this one gives me so much trouble. Wikipedia gives the equation for the enthalpy, but i have no clue how to write it that way :S
could anyone give me some clues to solve this one?
thanks

2. May 15, 2010

### phyzguy

There's an equation called the Sackur-Tetrode equation that expresses the entropy of an ideal gas S in terms of U. You can invert this to give U in terms of S, then substitute into your equation for H in terms of U and you will have H in terms of S.

3. May 15, 2010

### quantoshake11

oh, thanks! i just need to get the volume out of there, but i could use the other relations to do that. doh! i should've seen that earlier :P