Graham's Law of Diffusion
The rate at which a gas diffuses or effuses is inversely proportional to the square root of its molar mass.
Formula / equation
r₁ / r₂ = √(M₂ / M₁)
Unit
Dimensionless
In depth
Since all gases at a given temperature have the same average kinetic energy, lighter molecules must move faster and so escape or spread more quickly. The law provides a simple route to unknown molar masses and was the original basis for separating uranium isotopes.
Examples in the real world
Hydrogen diffuses four times faster than oxygen; ²³⁵UF₆ was enriched by repeated effusion through porous barriers.