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Isobaric expansion problem

  1. Oct 17, 2004 #1
    question: An ideal gas initially at 230 K undergoes an isobaric expansion at 3.65 kPa.

    If the volume increases from 1.7 m^3 to 6.8 m^3 and 25.1 kJ is transferred to the gas by heat, what is the change in its internal energy?

    i know that isobaric expansion means that the pressure is constant. however, i dont know how to calculate the internal energy. my proff went over this part very briefly and the book doesnt cover much about this topic.
  2. jcsd
  3. Oct 17, 2004 #2


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    Use the specific heat for an ideal gas at constant pressure.
  4. Oct 17, 2004 #3
    so internal energy = q+w

    work = -p*change in volume

    which is (3.65kpa*1000)(6.8m^3-1.70m^3)

    and q= n*Cp*change in T

    and Cp = 20.775 J/mol*K

    i know the initial T, and could find the final T
    n is also easy to find

    however, what does the 25.1 kj transferred to the gas by heat mean and how does it relate to this problem?
    Last edited: Oct 17, 2004
  5. Oct 17, 2004 #4


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    Heat (thermal energy) is being added to the system and the gas expands. As the gas expands it does work. The change in internal energy will be the difference between the heat added and the work done by the gas.
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