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Reviewing for the FE exam, came across questionable thermo problem.

  1. Apr 4, 2008 #1
    Im studying for the Fundamentals of Engineering exam (coming up April 12!!) and came across this Thermodynamics problem in my review book.

    So the work for an isothermal process is RTA*ln(VB/VA), where VA was previously determined to be 0.103m3.

    In the solution to the problem, the RTA term is replaced with PA*VA, where it should be (PA*VA)/n from the ideal gas law.

    Is this solution wrong? As I see it, this cant be solved without knowing the number of moles of gas (or mass of the gas depending on which R is used). I was unable to get the correct answer, and the solution seems wrong to me.
  2. jcsd
  3. Apr 4, 2008 #2


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    The solution should have replaced nRTA with PAVA. You don't need to know the amount of gas to solve this problem.

    EDIT: I get -18.8 kJ for the work done in the A-to-B process.
    Last edited: Apr 4, 2008
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