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Homework Help: Molar enthalpy of a gas at various temperatures

  1. Nov 23, 2011 #1
    1. The problem statement, all variables and given/known data
    I'm given the molar enthalpy of a gas at various temperatures.

    For each temperature, the enthalpy at 1 bar and 100 bars of pressure is listed.

    The question: The gas moves through a tube. The pressure in the tube is 100 bar. When the gas exits the tube, the pressure is 1 bar. (Hint: the enthalpy is conserved).

    What is the lowest temperature at which some liquefaction takes place?

    2. Relevant equations

    3. The attempt at a solution
    The chart says that at 1 bar and 77 K (liquid), the gas' enthalpy is -3407 J.

    At 1 bar and 77 K (gas), the gas' enthalpy is 2161 J.

    I think I'm supposed to find the temperature in the 100 bar part at which some liquifaction takes place. I am just not sure whether to use the liquid enthalpy or the gas enthalpy. Once I know the enthalpy, I can get the temperature.
  2. jcsd
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