Diffusion

Diffusion is the movement of molecules along a concentration gradient, from an area of high concentration to one of low concentration. Diffusion proceeds until the two concentrations are equal. Diffusion occurs in both gases and liquids.

Diffusion takes place not only in liquid solutions, but in gases. The odor of bread wafting through a house is an example of the diffusion of bread-smell chemicals from a high concentration to a lower concentration.