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Homework Help: Gas temperature from A->B->C

  1. Dec 1, 2011 #1
    1. The problem statement, all variables and given/known data

    The task is to get Q, that gas has received through A-B-C change?
    Second task is to get usefulness of the machine?

    http://img40.imageshack.us/img40/8372/toplinaabc.jpg [Broken]

    2. Relevant equations

    W=pV

    3. The attempt at a solution

    If I use W=pV i get 0 from A->B so i cant get usefulness. No idea.
     
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Dec 1, 2011 #2
    To get the heat energy in or out of system one requires the value of the number of moles of gas and the gas constant R or the temperatures at some points on the graph.
     
  4. Dec 1, 2011 #3
    So from A->B formula is PV=nRT then I get dT=((p2-p1)*v1)/nR?

    from B->C formula is W=p2(v2*v1) and with ideal gas dT=(p2(v2-v1))/nR?

    But how to get Q from that?
     
  5. Dec 1, 2011 #4
    from A->B formula is PV=nRT then I get dT=((p2-p1)*v1)/nR ...yes

    from B->C formula is W=p2(v2*v1) ...replace * by -

    dT=(p2(v2-v1))/nR ...yes

    To get the heat transfer one can use [itex]\Delta[/itex]U = [itex]\Delta[/itex]Q + [itex]\Delta[/itex]W where U is the internal energy.
     
  6. Dec 1, 2011 #5
    okay man, thanks!
     
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