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Essentially comparison of isothermal and adiabatic transformations

  • Thread starter arhont
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Homework Statement




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



Homework Equations



Ideal Gas Law, Thermo Laws.

The Attempt at a Solution



P1V1 --isotherm-->P2V2
P1V1 --adiabatic-->P3V2
If P2>P3, is V2>V1 or V2<V1?
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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.
 

Answers and Replies

  • #2
haruspex
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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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