# Graham's Law of Effusion when Looking at Samples with Equal Mass?

• Please ! Be serious ! $\ce{O2}$ and $\ce{N2}$ do not have the same mass ! – Maurice Feb 2 at 20:53
• Effusion is how isotopes of say UF$_6$ can separated. The rate of efflux of a gas with mol wt $m$ is $\rho\sqrt{RT/(2\pi m)}$ where $\rho$ is the gas density. Thus at the same density gasses undergo effusion as $1/\sqrt{m}$. (To be accurate this eqn. applies only if the mean free path is 10 times the size of the efflux pinhole.) – porphyrin Feb 3 at 9:42