Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Ideal gas processes

  1. Dec 30, 2011 #1
    How to calculate heat transfer to an ideal gas during isochoric process? I only know initial and final pressures and volume. (Do I have to know whole cycle (closed loop)?)

    Here, no work is done so:

    dU = dQ

    But T and its change is unknown, so what would be the next step?
  2. jcsd
  3. Dec 30, 2011 #2


    User Avatar
    Gold Member

    You should specify which C you are using Cp or Cv, as each ahs a spcific value.

    Also have you heard of the ideal gas equation, PV=nRT?
    That is the hint to get you started to the next step.
  4. Dec 30, 2011 #3
    As molar heat capacity I use "cv". Let's say an ideal gas is monoatomic, so "cv"=3/2 R.

    I involved equation pv=nRT as you suggested and figured something out:

    dU = dQ
    n*cv*ΔT = Q

    p*V = n*R*T
    dp*V + p*dV = n*R*dT (isobaric p. dV=0)
    ∫dp*V = ∫n*R*dT
    Δp*V = n*R*ΔT
    ΔT = Δp*V / (n*R)

    After substituting ΔT into the first integrated equation:

    Q = 3/2 *VΔp

    I got rid out of T and it seems correct, is it?
  5. Dec 30, 2011 #4


    User Avatar
    Gold Member

    Perfect firugring out !!
    But, you are missing an R in your final equation

    In any case, you could just leave as:
    Q = ( Cv/R ) V Δp
    and that would work for any ideal gas, momoatomic, diatomic, .... polyatomic
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook