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Isothermal Expansion of a Diatomic Gas

  1. Dec 3, 2014 #1
    1. The problem statement, all variables and given/known data
    A 0.300-kg sample of nitrogen gas (diatomic molecules,mN2 = 4.652 × 10^−26 kg) in a chamber fitted with a piston undergoes an isothermal expansion from 0.0500 m^3 to 0.150 m^3 .

    If the final pressure is 110 kPa, what is the final temperature?

    2. Relevant equations
    PV=N*kB*T where Boltzmann's Constant is kB=1.38*10^-23 J/K

    3. The attempt at a solution
    Because the process is isothermal, PV = constant and Ti = Tf.
    To use the formula, I need N (number of molecules).


    Plugging this N into T=PV/NkB I get, T = 92.7 K, which is not the right answer.

    I don't think diatomic gasses behave ideally, but I have no idea how to reflect that in the formula. I also do not know how the initial volume and pressures are relevant.
    Last edited: Dec 3, 2014
  2. jcsd
  3. Dec 3, 2014 #2
    The question is what is the final temperature if the final pressure is 110 kPa. Sorry, I'll edit.
  4. Dec 3, 2014 #3
    Just a thought, am I supposed to use the number of molecules or the number of atoms?
  5. Dec 3, 2014 #4


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  6. Dec 3, 2014 #5
    Well that clears it up. Thank you.
  7. Dec 3, 2014 #6
    N is the number of particles which can be molecules, atoms, ions etc.
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