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Thermodynamics - Carnot cycle

  1. Mar 22, 2014 #1
    1. The problem statement, all variables and given/known data
    An ideal gas is taken through a Carnot cycle. The
    isothermal expansion occurs at 250°C, and the isothermal
    compression takes place at 50.0°C. The gas takes in 1 200 J
    of energy from the hot reservoir during the isothermal
    expansion. Find (a) the energy expelled to the cold reservoir
    in each cycle and (b) the net work done by the gas in
    each cycle.


    2. Relevant equations



    3. The attempt at a solution

    Qh=1200J.

    Qh-W=Qc (absolute values)

    e(Carnot)=(523-323)/523= 61.9 %
    (corrected my typo from before)

    Therefore Qc= .381(1200J)=457J

    and W = 1200-457=743J

    Not the correct answer. Qc = 741 according to the solutions manual.

    ps. Latex seems to be bugged, didn't work in "preview post" mode.
     
    Last edited: Mar 22, 2014
  2. jcsd
  3. Mar 22, 2014 #2

    TSny

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    Hello. Check this calculation.
     
  4. Mar 22, 2014 #3
    Hi there.

    Woops I typed it in wrong, it was supposed to be (523-323)/523= .619

    The answer is still incorrect though.
     
  5. Mar 22, 2014 #4

    SteamKing

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    That's not the problem. Check the numbers. Remember, you are looking for a difference of 2 joules.
     
  6. Mar 22, 2014 #5
    Give me another hint, please. I still don't know what I'm doing wrong :). Is my logic even sound?
     
  7. Mar 22, 2014 #6

    TSny

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    e = (523-323)/523 is correct. But this does not equal .619
     
  8. Mar 22, 2014 #7
    what?! How did I miss that, I re-did it like 3 times :/. Thank you though.
     
  9. Mar 22, 2014 #8

    TSny

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    Also, to get the anwer of 741 J it appears that you should convert to Kelvin by adding 273.15 rather than 273.
     
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