[shoofy2]

I understand that the rate of effusion is indirectly related to the molecular weight, and this makes sense: as the mass of the molecules get smaller, the rate increases to maintain the same kinetic energy. But why is it the square root of the molar mass?

I expect it has something to do with the relationship between mass and velocity, as indicated by KE =(1/2)mv^2, but i can't quite tease out the solution.

Thanks!

[MrTeo]

Consider that at the same temperature different gases have the same kinetic energy and remember that the weight of a single molecule is directly proportional to the molar mass of the gas. You should be able to find easily the solution using the kinetic energy relation that you correctly pointed out