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Question of Thermodynamics

  1. Dec 13, 2014 #1
    < Mentor Note -- Posts split off from an old thread to preserve very good helpful responses...>

    how is heat path dependent?prove with an example?
     
    Last edited by a moderator: Dec 14, 2014
  2. jcsd
  3. Dec 13, 2014 #2

    rude man

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    Consider an ideal gas at initial state (p1,V1,T1). We want to change the state to (p2,V2,T2).

    We can do this in many ways, but let's pick two in particular :
    1. we can change the temperature at constant V1 (isochoric) until p = p2, then, holding p constant, change the temperature some more until V = V2. We have reached (p2,V2,T2).
    2. we can change the temperature at constant p1 (isobaric) until V = V2, then, holding V constant, change temperature some more until p = p2. We have again reached (p2,V2,T2).
    In both cases we went from state (p1,V1,T1) to (p2,V2,T2).
    Can you compute the heat and work required in both processes?
     
  4. Dec 13, 2014 #3
    thanx ...... but you did not clear the point that the heat is path dependent...means we go to the same state in both cases...but what is the difference in both cases that makes the heat path dependent....
     
    Last edited by a moderator: Dec 14, 2014
  5. Dec 13, 2014 #4

    rude man

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    The difference is in one case we change p first and then V, in the other we change V first and then p. The sequence makes it different. Compute W and Q for both cases and you will see.
     
  6. Dec 13, 2014 #5
    i could not do it :(
     
  7. Dec 13, 2014 #6

    rude man

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    What is the area under a p-V curve going from a state 1 to a state 2?
     
  8. Dec 13, 2014 #7
    I assume you are dealing with ideal gases. If the gases are in a rigid container, how much external work do the combination of gases do on the surroundings? Assuming that the container is adiabatic, how much heat passes through the walls of the container. From the first law of thermodynamics, what is the change in internal energy for the combination of gases when the system finally equilibrates? If the wall is mobile and diathermal, how do the temperatures and pressures in the two compartments compare at the final equilibrium state?

    Chet
     
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