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Enthalpy of ideal gas

  1. May 14, 2010 #1
    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?
  2. jcsd
  3. May 15, 2010 #2


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    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.
  4. May 15, 2010 #3
    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
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