Why do lighter gases diffuse faster than heavier gases?

Lighter gases diffuse faster than heavier gases due to their lower molecular mass and higher average speed.

Diffusion is the process by which particles spread out from an area of high concentration to an area of low concentration. This process is driven by the kinetic energy of the particles, which is directly related to their mass and speed. In gases, the particles are in constant, random motion and collide with each other and the walls of their container. The speed of these particles is determined by their kinetic energy, which is in turn determined by their temperature and mass.

Lighter gases have lower molecular masses than heavier gases. According to the kinetic theory of gases, at a given temperature, all gases have the same average kinetic energy. However, because kinetic energy is proportional to the mass and the square of the speed of the particles, lighter particles must move faster to have the same kinetic energy as heavier particles. Therefore, at the same temperature, lighter gases have a higher average speed than heavier gases.

This higher average speed means that lighter gases diffuse faster. When a gas is released into a space, its particles move randomly in all directions. The faster the particles move, the quicker they spread out and the faster the gas diffuses. Therefore, because lighter gases have a higher average speed, they diffuse faster than heavier gases.

Furthermore, the lower mass of lighter gases also means they are less likely to be slowed down by collisions with other particles. In a gas, particles are constantly colliding with each other and these collisions can slow down the particles. However, because lighter particles have less mass, they are less affected by these collisions and therefore maintain their high speeds, further contributing to their faster rate of diffusion.