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Homework Help: Pressure/Temp/Volume question

  1. Dec 10, 2009 #1


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    1. The problem statement, all variables and given/known data

    One mole of an ideal gas at 300K expands isothermally from a pressure of 2x10^6 N/m^2 to a pressure of 2x10^5 N/m^2.

    Derive the equations for, and calculate:

    the heat absorbed by the gas...
    the change in the internal energy of the gas...
    the entropy change in the gas if it expands reversibly

    2. Relevant equations

    ΔE = Q - W
    PV = nRT
    W = PΔV
    Another equation involving ΔE, but i am not sure what it is...

    3. The attempt at a solution

    Since it is an isothermic equation, there is no Δt...which makes the ΔE equal zero(the internal energy). Since the internal energy is zero, that makes the equation ΔE=Q-W into Q=W. I am not sure how to finish the problem, because i have a change in pressure...but there is no change in temperature....
  2. jcsd
  3. Dec 10, 2009 #2


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    Homework Helper

    Work is just the area under a PV diagram. Draw out the diagram, label V1 and V2 (the initial and final volumes), and you'll see what the area is.
  4. Dec 10, 2009 #3


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    how do i know what the change in volumes are? all i know is there is a pressure decrease, which could mean anything....unless i am missing something
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