Hydrogen has a molar mass of 2 g/mol and oxygen 32 g/mol. What is the ratio of their effusion rates?

1. Graham's law gives the rate of hydrogen over the rate of oxygen as the square root of the oxygen molar mass over the square root of the hydrogen molar mass. 2. Note the direction carefully: the heavier gas sits on top inside the square roots, because rate and mass run opposite ways. 3. Substitute the masses: the square root of 32 divided by the square root of 2. 4. Combine under one root: the square root of 32 over 2, which is the square root of 16. 5. That equals 4, so hydrogen effuses four times as fast as oxygen. 6. Answering 16 times faster means using the plain mass ratio and forgetting the square root altogether. _Source: OpenStax Chemistry (CC BY 4.0), Ch 9 "Gases", section 9.4 Effusion and Diffusion of Gases_