**Graham’s Law of Diffusion: **Graham in 1829, observed the spreading out or diffusion of gases. He postulated that the rate of the diffusion of the gas does not depend upon the gravity, but it depends upon the temperature of a gas. This law states that “rate of diffusion of a gas is inversely proportional to the Square root of the density of the gas at a given temperature.”

If we have two gases having rates of diffusion as r_{1}, r_{2}, with densities d_{1} and d_{2}, then

Dividing the two equations,

We also know that densities are directly proportional to the molar masses,

so,

## Graham’s Law Formula

It means that the rate of diffusion can be calculated from the densities of gases and molar masses of the gases.