Graham's Law of Effusion

📊 beginner

$$\frac{r_1}{r_2} = \sqrt{\frac{M_2}{M_1}}$$

Rate of effusion is inversely proportional to square root of molar mass.

Variables & Units

$r_1, r_2$

Effusion rates

Unit: $\text{mol/s}$ or $\text{m}^3/\text{s}$

$M_1, M_2$

Molar masses

Unit: $\text{g/mol}$

Key Information

📐 Derived From

Kinetic theory: average speed $\propto 1/\sqrt{M}$.

💡 Example

Compare He ($M=4$) and Ne ($M=20$): $r_{\text{He}}/r_{\text{Ne}} = \sqrt{20/4} = \sqrt{5} \approx 2.24$.

🔧 Applications

Isotope separation, gas leak detection.

⚠️ Constraints

Same temperature and pressure, small pinhole.

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