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Homework Help: Is the gas monatomic or diatomic?

  1. May 16, 2007 #1
    1. The problem statement, all variables and given/known data

    130 J of energy is supplied as heat to 3.00 moles of an ideal gas at constant pressure, the temperature rises by 4.00 K.

    Calculate the molar heat capacity at constant pressure, CP,m and the molar heat capacity at constant volume, CV,m for the gas.

    Is the gas monatomic or diatomic?

    2. Relevant equations

    Cp= Q/ T

    Cp= Cv + nR

    Cp,m = Cv,m +R

    3. The attempt at a solution

    Cp= Q/ T
    = 130/ 4= 32.5

    Cp= Cv + nR
    32.5 = Cv +3 (8.314)

    Cv= 7.558

    heat capacity at constant pressure Cp = 32.5
    at capacity at constant volume Cv = 7.558

    how do i go from here to calculate molar heat capacity..
  2. jcsd
  3. May 16, 2007 #2
    Divide Cp by the number of moles. Generally speaking, [tex]Cp=\frac{pdv}{ndt}+Cv[/tex] where Cp and Cv are molar heat capacities at constant pressure and volume.
  4. May 16, 2007 #3
    Cp = nR + Cv

    is nR= pdv/ ndt

    what is dv/dt that u have in your formula....is the rate of change of volume...

    or volume / temperautre?
  5. May 18, 2007 #4
    Volume by temperature. You can use the ideal gas equation, PV=nRT, to find it under what ever conditions that are imposed on your system.
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