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Cyclic thermodynamics processes

  1. Sep 16, 2012 #1
    1. The problem statement, all variables and given/known data
    Consider a cyclic process involving a gas. If the pressure of the gas varies during the process but returns to the original value at the end, is it correct to write [itex]ΔH=q[/itex]

    2. Relevant equations



    3. The attempt at a solution
    I'm actually not sure. q is a path function and H is a state function. To be honest I have no idea how to approach this problem, perhaps someone can give me a small hint.

    BiP
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Sep 16, 2012 #2

    ehild

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    How is a state of a gas defined? What is a state function?
    Suppose you have a function F(x,y,z) and F(1,2,3)=10 and then you let the variables change, but they return to the original values (1,2,3), what will be F(1,2,3)?

    ehild
     
  4. Sep 16, 2012 #3
    So the state of the system has not changed, so the [itex]ΔH [/itex] must be 0. But what about the heat? Must it also be 0?

    BiP
     
  5. Sep 16, 2012 #4

    ehild

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    If ΔH=q and ΔH=0 then what else can q be?

    ehild
     
  6. Sep 17, 2012 #5
    I'm sorry but I am not sure you read the OP. The question asked whether or not [itex] ΔH=q [/itex] ? How can you assume it to be true if you haven't shown it to be true?

    BiP
     
  7. Sep 17, 2012 #6

    ehild

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    You know that ΔH=0 in a cyclic process. Now you need to look after what q and ΔH are, and find out if the equation ΔH=q holds.

    ehild
     
    Last edited: Sep 17, 2012
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