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Physical Chem review

  1. Jan 22, 2017 #1

    IoFawkes

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    1. The problem statement, all variables and given/known data
    Calculate Work(w) when 6.5L of an ideal gas at an initial pressure of 34.3atm is expanded or compressed isothermally to a final volume of 34.3L reversibly. Answer in J

    2. Relevant equations
    PV=nRT
    P1V1=P2V2
    w=-nRT In(V2/V1)

    3. The attempt at a solution
    Using w=-nRT In(V2/V1)
    I'm not given mols or T, I know T=constant, since it's isothermal
    Can I use PV=nRT and substitute (PV) in for (nRT) in the equation: w=-nRT In(V2/V1) ?
    If so, what should I use for values of P and V? Final/Initial/delta?

    Io

    PS: This may be in the wrong place, the boundary seems unclear in Chem/Phys or Phys/Chem studies.
     
  2. jcsd
  3. Jan 22, 2017 #2

    TSny

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    Welcome to PF!
    Yes
    How does PV in the initial state compare to PV in the final state?
     
  4. Jan 22, 2017 #3

    IoFawkes

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    P1V1=P2V2 so it doesn't matter which I use as long as P and V are both initial values, or final values. Correct?
    EDIT: Except it's asking for work done, so would it be the Change in Pressure and Volume?
    Io
     
    Last edited: Jan 22, 2017
  5. Jan 22, 2017 #4

    TSny

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    Yes
    nRT is a constant for an isothermal process. At any point along the process, nRT has the same value. The ideal gas law tells us that for any state, nRT = PV. So, nRT for the isothermal process equals PV evaluated for any state along the isothermal process.

    nRT would not correspond to a change in PV.
     
  6. Jan 22, 2017 #5

    IoFawkes

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    Ah, that makes sense, thanks! How wonderful a change in perspective.

    Io
     
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