1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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
    C2T

    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

    User Avatar
    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.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook