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Homework Help: Change in Enthalpy when Internal Energy does not Change

  1. Nov 7, 2012 #1
    1. The problem statement, all variables and given/known data

    The internal energy of a perfect gas does not change when the gas undergoes isothermal expansion. What is the change in enthalpy?

    2. Relevant equations

    3. The attempt at a solution
    The answer is 0

    Since U, the internal energy, doesn't change, I assumed that the equation would be ΔH=PΔV. Why would PΔV equal 0 if there is an expansion (ΔV is not 0)? I'm guessing that I'm not seeing something here since this seemed to be a rather simple question.
  2. jcsd
  3. Nov 7, 2012 #2


    User Avatar
    Gold Member

    The enthalpy is actually [itex]\Delta H = \Delta U + \Delta (PV)[/itex]. I don't think that PV will change.
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