GRAHAM’S LAW OF DIFFUSION:
Diffusion means mixing up of molecules of different gases moving in opposite directions. We know that gas molecules are constantly moving in haphazard direction. Therefore when two gases are placed separated by a porous membrane, they diffuse through the membrane and intermingle with each other. Light gases diffuse more rapidly than the heavier one. Graham (1881) established a quantitative relationship between the rates of diffusion of gases and their densities and is termed as Graham’s law of diffusion.
This law states “Rate of diffusion of a gas is inversely proportional to the square root of the density of that gas provided the pressure and temperature are the same for the two gases”. This law is stated mathematically.
Where ‘r’ is the rate of diffusion and ‘d’ the density of the gas.
If we consider two gases, having densities d1 and d2 respectively; then;