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Thermochem, thermodynamics, diatomic gas at constant volume

  1. Feb 24, 2016 #1
    1. The problem statement, all variables and given/known data
    A sample consisting of one mole of a diatomic perfect gas is heated from 25 °C to 200 °C at constant volume. Calculate q, w, ΔU and ΔH for the process, given that Cv = 23.02 J K-1 mol-1 .

    2. Relevant equations
    Im studying for mid terms and i have no lecture notes on diatomic gas looking online currently haven't found much. Please explain

    3. The attempt at a solution
    du=w-cvdt
    cv=5/2nr
     
  2. jcsd
  3. Feb 24, 2016 #2
    You don't need to know what a diatomic gas is to solve this problem. They give you the value of the heat capacity. That's all you need.

    If the volume of gas is constant, how much work is done?

    What is that Cv doing that equation that you wrote? The equation is incorrect. It should read ΔU=Q-W
     
  4. Feb 24, 2016 #3
    wont it be du=q+w
    w=-pdv
    du=q-pdv
    du=qv at const volume .
     
  5. Feb 24, 2016 #4
    how do i find work , work it -pdv right? i wasnt given pressure or is it understood as 1 bar and i wasnt given a volume
     
  6. Feb 24, 2016 #5
    If the volume doesn't change, what is dv equal to?
     
  7. Feb 24, 2016 #6
    0, and because w=pdv no work is done ? is this an isochoric process? would du=n cvdt
     
  8. Feb 24, 2016 #7
    Very nice. Yes. isochoric is synonymous with constant volume. And your equation for the differential change in internal energy is correct.

    Chet
     
  9. Feb 24, 2016 #8
    i figured it out i got 4.028 kj
    w=0
    du=q+w
    du=Q
    q+du are the same
    dh=du +pdv
    q=ncvdt
     
  10. Feb 24, 2016 #9
    thank you ever so much
     
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