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Homework Help: Thermodynamics Problem

  1. Sep 30, 2010 #1
    1. The problem statement, all variables and given/known data
    [PLAIN]http://img821.imageshack.us/img821/8541/cheme.png [Broken]

    I am only looking for help in part a.

    2. Relevant equations

    PV = mRT


    3. The attempt at a solution

    By looking at the figure, I was able to calculate the volume of state 2, which is half of the volume of state 1.

    V1 = (mRT1)/P1
    V1 = (5*0.287*573)/200
    V1 = 4.11 meters cubed

    V2 = V1/2
    V2 = 2.06 meters cubed

    However, in order to calculate the temperature by using the Ideal Gas Law, I need pressure first. How do I go about finding pressure? Is there an assumption I'm supposed to make first?
     
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Sep 30, 2010 #2

    Mapes

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    How does the pressure arise initially? Can you connect a property of the piston to the pressure?
     
  4. Sep 30, 2010 #3
    Well, I guess that since the piston does not exert a force on the air, the pressure stays the same throughout state 1 and 2?

    Edit: Actually, the pressure arises from the weight of the piston and the atmospheric pressure. So since those two factors stay the same, the pressure is constant throughout states 1 and 2?
     
    Last edited: Sep 30, 2010
  5. Sep 30, 2010 #4

    Mapes

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    The piston doesn't exert a force on the air? Or the piston exerts a constant force regardless of its height?
     
  6. Sep 30, 2010 #5
    Yeah I edited my post, because I realized that since the atmospheric pressure and the weight of the piston are constant, the pressure doesn't change from state 1 to state 2. Thanks for the help.
     
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