If a gas line springs a leak, which will diffuse faster through the atmosphere and why: CH4 or C2H6? Rates of diffusion and effusion depend on the masses of the gases because average speeds determine these rates, and these are given 1/2 by Equation 2-5: Vrms = (3) For two M gases at the same temperature, the one with the smaller mass has the molecular speed and will Thus, CH4 diffuses through the atmosphere diffuse than C2H6