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Drawing a PV Diagram

  1. Jan 9, 2011 #1
    1. The problem statement, all variables and given/known data

    One mole of an ideal gas at an inital tempreature of 300K and pressure of 4 atm is carried through the following reversible cycle:

    a) It expands isothermally until its volume is doubled.
    b) It is compressed to its original volume at constant pressure.
    c) It is compressed isothermally to a pressure of 4 atm.
    d) It expands at constant pressure to its original volume

    Make a plot of this cycle process on a PV diagram and calculate the work done by the gas per cycle.

    2. Relevant equations

    3. The attempt at a solution

    Okay so step a. means that while Vo goes to 2Vo the pressure doubles as well, yes? And step b means that the pressure is the same but the volume goes to Vo. And so then step C should mean that since P is returning to its initial, the gas returns to Vo too, right? But if that's true, then D doesn't make sense since it has already returned to Vo.

    Please help! Once I get the diagram correct, I'm just going to use the area to find the work done.
  2. jcsd
  3. Jan 9, 2011 #2


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    Staff: Mentor

    Take a look at the PV = nRT equation. If T is held constant (isothermal), how must P and V relate to each other?

    Again, take a look at PV = nRT. What's the current volume and pressure when step C begins? How do P and V vary when the compression (or expansion) is isothermal?
  4. Jan 9, 2011 #3
    Oh okay haha. . .P has to be half. . .

    Thank you :)
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