<Dd> M is the molar mass of gas 2 . </Dd> <P> Graham's law states that the rate of diffusion or of effusion of a gas is inversely proportional to the square root of its molecular weight . Thus, if the molecular weight of one gas is four times that of another, it would diffuse through a porous plug or escape through a small pinhole in a vessel at half the rate of the other (heavier gases diffuse more slowly). A complete theoretical explanation of Graham's law was provided years later by the kinetic theory of gases . Graham's law provides a basis for separating isotopes by diffusion--a method that came to play a crucial role in the development of the atomic bomb . </P> <P> Graham's law is most accurate for molecular effusion which involves the movement of one gas at a time through a hole . It is only approximate for diffusion of one gas in another or in air, as these processes involve the movement of more than one gas . </P> <P> In the same conditions of temperature and pressure, the molar mass is proportional to the mass density . Therefore the rate of diffusion of different gases is inversely proportional to the square root of their mass densities . </P>

According to graham 's law effusion rate is inversely proportional to the square root of molar mass