Diffusion -- the spontaneous intermingling of one substance with another.
Effusion -- movement through an extremely tiny opening into a region of lower pressure.
Thomas Graham described the rate at which gases effuse.
The rate is described mathematically as an inverse square function; the rate effusion for a gas is inversely related to the square root of its mass. If the absolute temperature of the two gases is equal, then so are their kinetic energies (KE=0.5mv2). Graham's law can be derived algebraically by setting the kinetic energies equal and solving for the ratio of velocities (a good practice exercise!)
