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Calculating work in a one-step expansion/compression

  1. Feb 14, 2009 #1
    Hello. I'm having problems with one thermodynamics. I've used several equations but I'm still unable to get the right answer. A push in the right direction would be helpful. Thanks.


    Consider a process involving 1 mole of an ideal gas that takes place by the following pathway, at a constant temperature of 25oC:
    P1 = 3 atm → P2 = 0.75 atm → P3 = 3 atm
    Both steps occur irreversibly.

    work=?
     
  2. jcsd
  3. Jun 26, 2009 #2
    W=P[delta]V

    Boyle's Law: P1V1=P2V2

    PV=nRT


    So, use the ideal gas equation (PV=nRT) to solve for the initial volume of gas present. Then you can use Boyle's law to calculate the new volume after the change has occurred (the new volume is V2, the initial pressure is P1, etc) you can then multiply the new pressure by the CHANGE in volume (ie, the difference between V1 and V2) to get the work. Repeat process for the next step of the transfer. If you only need to calulate work for the net transition, completely ignore the middle step.
     
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