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Internal energy of system

  1. Nov 4, 2011 #1
    1. The problem statement, all variables and given/known data
    What happens to the internal energy of a system and its temperature when mechanical work is done on it?

    2. Relevant equations
    ΔU=Q-W

    3. The attempt at a solution
    First Law of Thermodynamics say:the change in internal energy of the system is equal to the heat added to the system minus the work done by the system ΔU=Q-W
    but what happen to the internal energy and temperature when mechanical work is done ON the system?
     
  2. jcsd
  3. Nov 4, 2011 #2
    As the equation for the 1st law of thermodynamics shows, what happens when mechanical work is done on a system depends also whether heat enters or leaves the system.
     
    Last edited: Nov 4, 2011
  4. Nov 4, 2011 #3
    the part which is confusing me is the 1st law of thermodynamics say,the work is done by the system ,but the question clearly say the work is done on the system.
    will it not have effect on the temperature within system?
     
  5. Nov 4, 2011 #4
    Assume that there is no heat transfer out of, or into, the system.

    Then when work is done ON the system, energy must be applied TO the system and hence its internal energy increases.

    But when work is done BY the system, energy must be supplied BY the system and hence its internal energy decreases.
     
  6. Nov 4, 2011 #5
    in that case what would happen to the temperature within system?
     
  7. Nov 4, 2011 #6
    If the internal energy of the system increases the temperature will increase.
     
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