Download - Diffusion and Effusion - WCS

11.4.notebook June 03, 2018

Diffusion and Effusion• The constant motion of gas molecules causes them tospread out to fill any container they are in.• The gradual mixing of two or more gases due to theirspontaneous, random motion is known as diffusion.• Effusion is the process whereby the molecules of agas confined in a container randomly pass through atiny opening in the container.

Graham’s Law of Effusion• Rates of effusion and diffusion depend on therelative velocities of gas molecules. The velocity of agas varies inversely with the square root of its molarmass.


All gases at the same temperature have the same average kinetic energy. Therefore, heavier molecules have slower average speeds. Graham’s law states that molecular speeds vary inversely with the square roots of their molar masses. Thus, the gases are ranked from heaviest to lightest in molar mass.