1. The problem statement, all variables and given/known data Okay... everywhere i look, it keeps talking about Boyle's Law applied to THE SAME gas! It's so frustrating and retarded! I get it, p1V1 = p2V2. Yay... I didn't even need to look THAT up! But my question is, how do you compare 2 different (ideal) gases?? It seems like such an obvious problem to address, but google searching just yields pages and pages of what I said above, rather than addressing this... Grr. Anyway, if I have 2 different containers of gasses, and they're in thermal contact, how do I work with Boyle's Law? (This is for my thermodynamics course.) My book says that Boyle's Law together with Avagdro's Law implies that p/n is the same for all ideal gases (where n is particle density, N/V). But this is completely NOT obvious to me. How do I prove this? Is it supposed to be intuitive?? Specifically, my example problem asks this... you have nitrogen at 1.26 kg/m^3 at pressure 1 bar and helium at 0.36 kg/m^3 at pressure 2 bar. Molecular weight of nitrogen = 28 and of helium = 4. Are the two gases in thermal equilibrium? 2. Relevant equations pV = k 3. The attempt at a solution Well, the solution is already given in the book (since it's a sample problem), but it doesn't explain why p/n is the same for all gases at same temperature -- it just states it as if it's obvious or something -- and I don't see why that necessarily is obvious, so... how do I prove that it is true? And am I the only one to whom this is not intuitive?? Thanks a lot!