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Temperature change in gasses

  1. Feb 18, 2014 #1
    Hello,
    I just have a question.
    When a gaz expands against a piston (that is insulated), the system is doing work so W>0 and we know that the volume will increase and the pressure decrease.

    But what I want to know, is how about the temperature, I'd say that it will decrease since the pressure also decreases , but is there any other argument ?

    I know that if we want to maintain a constant temperature in such a system we have to "connect" the system to a tank , so that the heat transfer will compensate the work done by the system.

    Thanks !
     
  2. jcsd
  3. Feb 18, 2014 #2

    vela

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    As you noted, a pressure decrease can occur while the temperature remains constant, so saying decreasing pressure implies decreasing temperature isn't a good argument. Think instead about what happens to the internal energy of the gas if Q=0 and W>0.
     
  4. Feb 19, 2014 #3
    We have that dE=-W
    Ef-Ei = -W <0
    We must have Ef<Ei that means that the kinetic energy in the final state is <
    So the temperature decreases
     
    Last edited: Feb 19, 2014
  5. Feb 19, 2014 #4

    vela

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    Yup.
     
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