According to the second law of thermodynamics, molecular movement of a substance takes place from a region of higher free energy of the’ molecules to a region of lower free energy. So any factor that affects the free energy also affects the rate of diffusion. The factors that affect the rate of diffusion of gases are described below.

i. Temperature

The rate at which a gas will diffuse increases with increase in temperature an increase in temperature increases the kinetic energy of the gas molecules i.e. raise in temperature is accompanied by an increase in the velocity at which the gas molecules move.

ii. Density of the diffusing gas molecules the rate of diffusion of any gas is inversely proportional to the square root of its density.


Where ‘r’ stands for rate of diffusion of gas’d’ stands for density of the gas.

iii. Medium in which diffusion occur

The more concentrated a medium is, the slower molecules will diffuse through it.

iv. Diffusion pressure gradient


In general, steeper the diffusion pressure gradient, the faster is the rate of diffusion.

v. The size and mass of the diffusing particles

If the size and mass of the diffusing particles is smaller, the rate of their diffusion will be faster.

The factors controlling the rates of diffusion of gases, in general, control the rates of diffusion of liquids and solids. In addition to the above mentioned factors, the diffusion of solutes in solvents, liquids in liquids and gases in liquids is influenced by the size and solubility of the diffusing molecules.


Diffusion of more than one substance at the same time and place may be at different rates and in different directions and is independent of each other.