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Free expansion of a Van der Waal's Gas

  1. Feb 1, 2010 #1
    1. The problem statement, all variables and given/known data

    There are two vessels connected by a stopper. Both have the same volume. One has "N_a" moles of gas, the other "N_b". Find the expression for the change in temperature when the stopper is opened and the system is allowed to come to a new equilibrium state.

    3. The attempt at a solution

    I'm supposed to use this equation: [tex] u = C_vT - a/v + const[/tex]

    I tried doing this: [tex]dt/dv = (du/dv) / (du/dt)[/tex] were the denominator is just Cv, but that just gave me:

    [tex]-a/v^2 * 1/C_v[/tex]

    The answer is supposed to look like:

    [tex](2n_an_b - n^2_a - n^2_b)*a/(c_v*2V[n_a + n_b])[/tex]

    How do I get the # of moles into this expression? Thanks.
  2. jcsd
  3. Feb 1, 2010 #2
    Any help please?
  4. Feb 2, 2010 #3
    I am having trouble with this too :S
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