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Seeming simple Thermodynamics problem

  1. May 13, 2012 #1
    A balloon is inflated with 5 liters of monatomic gas at 0 degrees Celsius and heated to 60 degrees Celsius at 1 atm. pressure.
    R=8.31J/mol K, Cp=5R/2, and Cv = 3R/2




    1. If the balloon does not expand, the heat absorbed by the gas would be what?



    2. If the balloon expands freely at constant pressure, the work done by the gas would be what?

    ...Took me a while, but I figured it out (no mass is entering the system). So here is the solution in case others want to know.

    For #1 PV=nRT
    P=1 atm=1.01*10^5 Pascals
    V=5 liters=.005 m^3
    n=Unknown
    R=8.31 J/mol K
    T=273K, Given

    Solving for n, we get .222601 mols

    ΔU=nCvΔT --constant volume
    ΔU=n*3R/2*60= 166J roughly


    For #2

    ΔU=nCpΔT
    ΔU=277.47
    ΔU=Q+W
    W=111J
     
    Last edited: May 13, 2012
  2. jcsd
  3. May 13, 2012 #2
    You'll have to take into account the mass flowing into the system. There may also be boundary work involved.
     
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