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Homework Help: Change in the internal energy of an isobaric process

  1. Sep 18, 2016 #1
    1. The problem statement, all variables and given/known data
    A cylinder contains 0.250mol of carbon dioxide (CO2) gas at a temperature of 27.0∘C. The cylinder is provided with a frictionless piston, which maintains a constant pressure of 1.00atm on the gas. The gas is heated until its temperature increases to 127.0∘C. Assume that the CO2 may be treated as an ideal gas.

    2. Relevant equations
    ΔU = ΔQ -W

    ΔU = C_v*n*ΔT

    3. The attempt at a solution
    In this case, I thought that ΔU could be set equal to (5/2)nRΔT since we know all of those variables. The value I got for that was ΔU = 520J, but that isn't the correct answer. Any help in explaining where I am going wrong would be appreciated greatly!
  2. jcsd
  3. Sep 18, 2016 #2
    Did you look up the value of Cv on line or in the literature?
  4. Sep 18, 2016 #3
    Whoops, to answer that, I did. The value I looked up however was not in units of moles, so I got the wrong answer. Found a value of Cv in moles and got the right answer.
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