Graham's Law of Diffusion and Effusion

　　Graham's law states that the rates of effusion of two gases are inversely proportional to the square roots of their molar masses at the same temperature and pressure:

　　Effusion is the term used to describe the passage of a gas through a tiny orifice into an evacuated chamber, as shown in the figure below.

　　The rate of effusion measures the speed at which the gas travels through the tiny hole into a vacuum. Another term to remember for the test is diffusion. Diffusion is the term used to describe the spread of a gas throughout a space or throughout a second substance.