Graham's Law of Effusion
Also known as effusion rate · diffusion rate ratio
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At the same temperature all gases carry the same average kinetic energy, so lighter molecules must move faster — and escape through a pinhole sooner. Thomas Graham quantified this in 1848: effusion rate scales with the inverse square root of molar mass. Helium leaks out of a latex balloon overnight while air barely follows, and the Manhattan Project exploited the tiny rate difference between ²³⁵UF₆ and ²³⁸UF₆ to enrich uranium through thousands of diffusion stages.
Graham's Law of Effusion
Where
- = Effusion rate of gas 1
- = Effusion rate of gas 2
- = Molar mass of gas 1
- = Molar mass of gas 2
Missing one of these? Work it out first, then come back
- Effusion rate of gas 1 — Volumetric Flow Rate (Q = Av), Poiseuille's Law
- Effusion rate of gas 2 — Volumetric Flow Rate (Q = Av), Poiseuille's Law
- Molar mass of gas 1 — Moles from Mass (n = m/M), Gas Density from Molar Mass
- Molar mass of gas 2 — Moles from Mass (n = m/M), Gas Density from Molar Mass