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Homework Help: Thermodynamics Cycle of Processes

  1. Apr 9, 2014 #1
    1. The problem statement, all variables and given/known data
    A certain fluid of mass 1kg undergoes a cycle of processes in a piston and cylinder device as follows:

    Process A-B: 70kJ of work done on the fluid. 35kJ of heat rejected to surroundings

    Process B-C: 50kJ of heat transferred to the fluid. No change in internal energy of system.

    Process C-A: 100kJ of work done by the fluid, fluid returns to the initial state.

    Calculate the heat transferred to or from the fluid in process C-A.

    2. Relevant equations
    I know that ΔU=Q-W is a relevant equation as I have been able to work out the other parts of this question that I have not written here with it, this part is actually the first part of the question but I am finding it the hardest to see what to do here :redface:

    3. The attempt at a solution
    I dont know whether you are supposed to use some of the values listed in Process A-B again or am I missing something?
  2. jcsd
  3. Apr 9, 2014 #2
    What you're missing is that, for a cyclic process, the sum of the three ΔU's has to be zero.

  4. Apr 9, 2014 #3
    Ah thank you very much for pointing that out! Much appreciated!
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