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Thermodynamics (work)

  1. Oct 24, 2013 #1
    i'm trying to relate the helmholtz and the gibbs free energy together. I thought that since the gibbs was just the W(other) and the helmholtz was the total work, that the following would be true.

    F=G-PdV

    because.. i thought that PdV was the work due to pressure, but it turns out that it's actually PdV+VdP which is just d(PV)

    but i thought PdV was the only term that was the work due to pressure, how is VdP work due to pressure? V is constant!
     
  2. jcsd
  3. Oct 24, 2013 #2

    Nugatory

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    Staff: Mentor

    V is not constant if dV is non-zero, right? Indeed, if V were constant the pressure wouldn't be doing any work (just as a weight sitting stationary on a rigid table does no work on the table).
     
  4. Oct 24, 2013 #3
    i know dV isn't zero, this is what gives rise to a displacement in the system which ultimately gives rise to work.
    i was referring to V, not dV. for the VdP term, i thought we were keeping V constant and varying P.
     
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