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Homework Help: Isothermal Compression and Entropy Change

  1. Feb 28, 2012 #1
    1. The problem statement, all variables and given/known data

    A 740g quantity of an ideal gas undergoes a reversible isothermal compression at a temperature of 330 K. The compression reduces the volume of the gas from 0.40 m3 initially, to 0.32 m3 finally. The entropy change of the gas is equal to:

    A) -43 J/K B) -150 J/K C) 43 J/K D) 150 J/K E) 0 J/K

    2. Relevant equations

    ΔS = nR*ln(Vf/Vi)

    3. The attempt at a solution

    I actually know exactly how to solve this problem. The only thing is, I haven't been able to determine n, the number of moles, without being given the molar mass.
    Is there some method to determine n that I'm missing, or has my prof omitted a vital piece of information (the molar mass)?
  2. jcsd
  3. Feb 29, 2012 #2

    Andrew Mason

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    Science Advisor
    Homework Helper

    You need the molar mass.

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