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PV Diagram help - Monatomic ideal gas change of state

  1. Jan 4, 2013 #1


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    1. The problem statement, all variables and given/known data
    Suppose a monatomic ideal gas is changed from state A to state D by one of the processes shown on the PV diagram (attached). a) Find the total work done on the gas if it follows the constant volume path A-B followed by the constant pressure path B-C-D. b)Calculate the total change in internal energy of the gas during the entire process and the total heat flow into the gas.

    2. Relevant equations

    W= -P(Vf-Vi)
    dU = Q + W
    dU = 3/2nRT

    3. The attempt at a solution
    I found the answer to part A to be 1215.6 J of work were done on the gas. My problem comes in part b. How can I determine the change in internal energy without knowing the number of moles (n) of the gas, or the temperature?

    Attached Files:

    • gas.png
      File size:
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  2. jcsd
  3. Jan 4, 2013 #2
    Do you really need n to calculate the change in internal energy? Remember that U depends only on temperature, so what is the temperaure difference?
  4. Jan 4, 2013 #3


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    Shouldn't that be dU = 3/2nRdT? Or ΔU = Δ(3/2nRT)? Maybe you can use the ideal gas law to write this in terms of P and V rather than nRT.
  5. Jan 5, 2013 #4


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    I think I was over-complicating the problem, but I've solved it now.

    Thank you for the help!
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