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Molar heat capacity at constant pressure/volume

  1. Mar 14, 2017 #1

    I am being stupid but cannot work out these problems:

    1. Energy supplied to 2.0 moles of an ideal gas is 117J and it changes the temperature by 2.0K (at constant pressure).

    2. Calculate both molar heat capacities at constant P and V.

    3. Firstly, I divided 117J by 4 to get the energy required to change 1 mole by 1k. Answer was 29.25J/m/K. Seems way too simple? Then, I have:

    Cp = Cv + nR, as we know that Cp is usually higher. So 29.25J/m/K = Cv + nR

    I know n = 2.0 moles, but the question doesn't give R. Or should I know R? Or am I completely wrong?

    Sorry if this is a basic question.


  2. jcsd
  3. Mar 14, 2017 #2


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    Science Advisor

    Yes, you are expected to know R. By the way, you weren't going to use n = 2, were you?
  4. Mar 14, 2017 #3
    Thank-you mjc

    And yes, I was. Cheers for the heads up. I didn't spend enough time on this module so trying now to catch up. I will revisit it and find out what n refers to.
    Cheers again :)
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