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Easy Thermo Question

  1. Feb 26, 2007 #1
    An Ideal monatomic gas at initial temperature [tex]T_0[/tex] (in Kelvins) expands from initial volume [tex]V_0[/tex] to volume [tex]2V_0[/tex] by each of the 5 processes indicated in the T-V diagram. In which process is the expansion a.)isothermal, b.) isobaric or c.)adiabatic? Explain your answers.
    d.) In which process does the entropy of the gas decrease.

    So far Ive said that AE is isothermal, initial and final temperatures are the same.

    AC is isobaric, Pressure remains constant

    AE is adiabatic, no heat flows in or out of the sytem

    Is this right?

    I dont know what to do for d.)...

    Attached Files:

    Last edited: Feb 26, 2007
  2. jcsd
  3. Feb 26, 2007 #2
    huh??? Could you restate the question.
  4. Feb 26, 2007 #3
    wow, sorry. I dont know how that happened? I only hit reply once.

    *edit* problem resolved
  5. Feb 26, 2007 #4
    Is adiabatic expansion a heating or cooling process?
  6. Feb 26, 2007 #5
    See edited original post and Attachment.
  7. Feb 27, 2007 #6

    Andrew Mason

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    I can't see your diagram yet, but I expect there are 3 choices: a horizontal line (T = constant), a curve where T/V = constant and a curve that goes below that (lower final T) where [itex]T/V^{\gamma-1}[/itex] = constant. I think you can determine from that whether your answers are right.
    For adiabatic dS = dQ/T = 0. But for the others, which way does the heat flow?

    Last edited: Feb 27, 2007
  8. Feb 27, 2007 #7

    Andrew Mason

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    Now that I see your graphic of the question, you should check your answer to c).

    If volume increases and temperature remains constant, dU does not change but the system does work (dW = PdV). So what can you say about dQ? What is the condition for dQ if it is adiabatic?

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