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Homework Help: Essentially comparison of isothermal and adiabatic transformations

  1. Nov 13, 2012 #1
    1. The problem statement, all variables and given/known data

    Two identical samples of ideal gas are initially at P1 and V1. The first sample undergoes an isothermal transformation to P2, V2 and second sample undergoes an adiabatic transformation to P3, V2. If P3<P2, is V2 higher or lower than V1? Explain

    2. Relevant equations

    Ideal Gas Law, Thermo Laws.

    3. The attempt at a solution

    P1V1 --isotherm-->P2V2
    P1V1 --adiabatic-->P3V2
    If P2>P3, is V2>V1 or V2<V1?
    For isotherm we have ΔU=Q+W, but since there is ΔT=0, then via 1st law of Thermo - ΔU=0 and Q=-W.
    For adiabatic we have constant heat, Q=0, W=PΔV, ΔU=W=PΔV. Yet... it seems useless. My gut tells me V2>V1, though somehow I am having trouble wrapping my mind around it.
  2. jcsd
  3. Nov 13, 2012 #2


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    Science Advisor
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    Gold Member

    There are two very useful equations relating pressure and volume, one for isothermal and one for adiabatic. You've met these, I would think.
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