Graham's Law of Effusion/Diffusion (r₁/r₂ = √(M₂/M₁))
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r₁/r₂ = √(M₂/M₁)
What each symbol means
| Symbol | What it stands for |
|---|---|
| M₁ | Molar mass of gas 1 (kg/mol) |
| M₂ | Molar mass of gas 2 (kg/mol) |
| r₁ | Rate of effusion/diffusion of gas 1 |
| r₂ | Rate of effusion/diffusion of gas 2 |
When to use this
At same T and P. Lighter gas diffuses/effuses faster. Rate ∝ 1/√M ∝ vrms. Also r₁/r₂ = √(ρ₂/ρ₁) using densities. Used in uranium enrichment (UF₆ isotope separation). Valid for ideal gas behavior through small orifice (effusion) or across concentration gradient (diffusion).