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Homework Help: Thermodynamics - Finding Entropy

  1. Nov 3, 2011 #1
    1. The problem statement, all variables and given/known data

    For a material given by U=C1PV2 and PV2=C2T
    Find the entropy

    2. Relevant equations

    dS/dU = 1/T; dU/dV = -P

    I don't know if I require anything else

    3. The attempt at a solution

    So from 2 equations I got U = C1

    But dU/dT is not equal to S. Which equation do I use to get the entropy? I was thinking of using F = U-TS. Which will give F = C1PV2 - TS And then doing dF/dT but then I didn't use the 2nd condition at all.

    What am I missing?
  2. jcsd
  3. Nov 4, 2011 #2

    I like Serena

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    Homework Helper

    Hi lifeonfire! :smile:

    Your relevant equations are not always true, the first requires V to remains constant, while the second requires S to remain constant.

    For reversible processes, the equation dU=TdS-PdV is true without conditions on state variables.
    From this you can isolate dS, apply the formulas given for your material, and integrate.
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