Graham’s law of effusion

Definition

Graham’s law of effusion states that the rate of effusion of a gas is inversely proportional to the square root of its molar mass. This means lighter gases effuse faster than heavier gases.

5 Must Know Facts For Your Next Test

1. Graham's law can be mathematically expressed as $\frac{\text{Rate}_1}{\text{Rate}_2} = \sqrt{\frac{M_2}{M_1}}$, 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 respective molar masses.
2. Effusion is the process by which gas molecules escape through a tiny hole into a vacuum without collisions between molecules.
3. The law is named after Thomas Graham, who formulated it in 1848.
4. Graham's law is applicable only under conditions where intermolecular forces are negligible and the gas behaves ideally.
5. Diffusion, which is different from effusion, involves gas molecules spreading out due to random motion and mixing with other gases.

Review Questions

• What does Graham's law of effusion state about the relationship between the rate of effusion and molar mass?
• How can you mathematically express Graham's law?
• Explain how Graham's law applies to two different gases with known molar masses.

Related terms

Effusion: The process by which gas molecules pass through a tiny opening into an evacuated space without significant collisions.

Diffusion: The process by which gas molecules spread out in response to concentration gradients, resulting in mixing.

Ideal Gas Law: $PV = nRT$, an equation representing the state of an ideal gas where $P$ is pressure, $V$ is volume, $n$ is moles of gas, $R$ is the universal gas constant, and $T$ is temperature.