Written by the Fiveable Content Team • Last updated August 2025
Written by the Fiveable Content Team • Last updated August 2025
Definition
Effusion is the process by which gas particles pass through a tiny opening from one container to another. It occurs when gas molecules escape from a container into a vacuum or less pressurized area through a small hole.
Effusion rate is inversely proportional to the square root of the molar mass of the gas, according to Graham's law.
Graham's law of effusion mathematically states that $\text{rate}_1 / \text{rate}_2 = \sqrt{M_2 / M_1}$, where $\text{rate}_1$ and $\text{rate}_2$ are the effusion rates of gases 1 and 2, and $M_1$ and $M_2$ are their molar masses.
Lighter gases effuse faster than heavier gases due to their lower molar mass.
Effusion differs from diffusion in that effusion involves movement through a small hole, whereas diffusion involves spreading throughout a space.
Real-life applications of effusion include separation of isotopes in nuclear processes and leakage detection in containers.