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Homework Help: How to read the PiVi^gamma = PfVf^gamma formula?

  1. May 7, 2012 #1
    1. The problem statement, all variables and given/known data

    An ideal monatomic gas is held initially at a pressure of 1 atmosphere in a volume of 10L. It is compressed to 4L in an adiabatic process.
    There are 0.8 moles.
    Find the final pressure of the gas.
    gamma = 1.667

    2. Relevant equations

    PiVi^gamma = PfVf^gamma

    3. The attempt at a solution

    I pretty much know what I'm doing, except I'm not sure what the formula means! Does it mean (PiVi)^gamma, or (Pi).(Vi^gamma?)

    I always assumed it was the second, but I'm doubting it now. I got a huge answer (10,190 x 10^5 Pascals) and I'm not sure if it's reasonable.

    Thank you!
  2. jcsd
  3. May 7, 2012 #2


    User Avatar
    Science Advisor

    The way you wrote it, it is (pi)(Vi)^gamma.

    Further, the Wikipedia article on "adiabatic processes", http://en.wikipedia.org/wiki/Adiabatic_process
    says that an adiabatic process gives [itex]PV^{\gamma}= Constant[/itex] so the way you have written it is correct- it is only the volume that is raised to a power.
  4. May 7, 2012 #3
    Okay, thank you very much! Thats what I thought it must be :) Great!
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