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.