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Homework Help: Gibbs Free Energy, Maxwell Relations

  1. Dec 10, 2015 #1
    1. The problem statement, all variables and given/known data
    We have a Gibbs Free Energy function G=G(P, T, N1, N2) I am not writing the whole function because I just want a push in the right direction. Find expressions for the entropy, volume, internal energy, enthalpy and chemical potential.

    2. Relevant equations
    Maxwell Relations
    T=(dU/dS) V and Ni constant
    -P=(dU/dV) S and Ni constant
    T=(dH/dS) P and Ni constant
    V=(dH/dP) S and Ni constant

    3. The attempt at a solution
    I have found entropy, volume and chemical potential (partial molar gibbs free energy) functions using related equations. But I'm not sure on how to derive internal energy and enthalpy expressions.
    If I try to make use of above equations, for an example first equation dU=TdS so U=T.dS
    but also from second equation dU=-PdV so U=-PdV

    Can both be correct at the same time? I think they would yield different equations.

    If I am going absolutely wrong, do you have any idea on how to find U and H expressions. What other relations could be used?
  2. jcsd
  3. Dec 10, 2015 #2
    For H, start with dG=-SdT-VdP+μ1dN12dN2, and substitute S=(H-G)/T. Then consider dP=0, dN's = 0.
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