How do gases with different molecular masses diffuse in air?

Gases with different molecular masses diffuse in air at different rates, with lighter gases diffusing faster than heavier ones.

In more detail, the process of diffusion involves the movement of particles from an area of high concentration to an area of low concentration. This is a natural process that occurs until the particles are evenly distributed throughout a space. The rate at which gases diffuse is influenced by several factors, one of which is the molecular mass of the gas.

According to Graham's law of diffusion, the rate of diffusion of a gas is inversely proportional to the square root of its molar mass. This means that lighter gases, or those with a smaller molecular mass, will diffuse more quickly than heavier gases with a larger molecular mass. For example, helium (He) with a molar mass of 4 g/mol will diffuse faster than oxygen (O2) with a molar mass of 32 g/mol.

The reason for this is due to the kinetic energy of the gas particles. All gas particles, regardless of their size or mass, have the same average kinetic energy at a given temperature. However, lighter particles move faster than heavier ones because they have less mass to move. Therefore, they can spread out and mix with other gases more quickly.

In summary, the molecular mass of a gas significantly affects its rate of diffusion in air. Lighter gases with smaller molecular masses diffuse faster than heavier gases with larger molecular masses. This is a fundamental concept in the study of gases and their behaviour, and it's crucial for understanding many natural and industrial processes where gas diffusion plays a key role.