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Homework Help: Isothermal and reversible expansion work problem (Physical Chem)

  1. Sep 20, 2007 #1
    1. The problem statement, all variables and given/known data
    A sample of 2.00 mol. CH3OH (g) is condensed isothermally and reversibly to liquid at 64*C. The standard enthalpy of condensation of methanol @ 64*C is -35.3 kJ/mol. Find w and q for the reaction.

    2. Relevant equations
    w = -nRT * ln(Vf/Vi) (although I don't have volume so I don't know how to find it)

    3. The attempt at a solution

    Honestly I can't find any other reversible/isothermal condition work formulas to use. I am sure I am just missing how to calculate volume here. I have n, R, and T but am not given V. Not sure if this can be calculated?
  2. jcsd
  3. Sep 21, 2007 #2


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    What is the volume of 2 mol of methanol at 64C? Make an assumption about it's density and calculate it (I assume you know how to convert moles to mass). Same thing goes for the volume of 2 moles of gas (methanol before condensation). The ideal gas equation might not be completely accurate but it is a good place to start.
  4. Sep 24, 2007 #3
    Well, I am stuck on the same problem. I don't think that the ideal gas expression is the correct one.... also, what do you get if you do 64 kJ/mol * 2 mol ? (I think this is the enthalpy for the reaction). And then, should you go back to the Van der waals equation for the real gas and implement that in your calculation of work ?
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