Graham's Law of Effusion
The law stating that rate of effusion or diffusion of a gas is inversely proportional to square root of its molar mass.
Governing formula
Rate1 / Rate2 = √(M2 / M1)
SI unit
mol/s or m³/s
In depth
Derived from equipartition: at same temperature, lighter molecules move faster on average ($v_{rms} ∠1/√{M}$) and escape pinholes faster.
Examples in the real world
Helium gas ($M=4$) effusing through a balloon latex pinhole 2.67 times faster than nitrogen gas ($M=28$).