1. Limited time only! Sign up for a free 30min personal 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!

VdP term in definition of constant volume specific heat

  1. May 3, 2016 #1
    1. The problem statement, all variables and given/known data
    I know that for constant volume ∂q=du and so du=Cv.dT
    However i dont understand how did we get to ∂q=du by neglecting the vdP term of enthalpy
    What im trying to say is, is enthalpy this ∆U+P∂V+V∂P or this ∆U+P∂V? I dont understand since the definition of enthalpy is derived out of a constant pressure volume change
    And why snt specific heat at constant volume Cv=∆U+V∂P/dT instead of Cv=∆U/dT?

    Thank you in advance for your answers
    2. Relevant equations


    3. The attempt at a solution
    From what I see:
    ∂Qnet,in=∆U+∂Wnet,out
    ∂Qnet,in=∆U+P∂V+V∂P

    C=∂Qnet,in/dT

    For constant pressure:
    Cp=∆U+P∂V/dT assuming ∆U+P∂V is enthalpy then ∆H=Cp.∆P

    For constant volume:
    Cv=∆U+V∂P/dT but all the books say it actually is just ∆U/dT
    where did the VdP term go? if we add heat to a fixed volume won't its pressure increase and so VdP would be relevant?
     
  2. jcsd
  3. May 3, 2016 #2
    dW = PdV, not d(PV).
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: VdP term in definition of constant volume specific heat
Loading...