Diffusion is, simply speaking, the spread of
particles from a
lower concentration to a
higher one. Diffusion takes place in both
gases and
liquids, and is especially noticeable if you put two different coloured
liquids together in a
glass. Due to the
random motion of the
particles, the two colours will mix into each other until the mixture is
uniform. The connection between concentration of the diffusing substance and its
rate of
diffusion was first formulated by
Adolf Fick.
J = DA(C1-C2)/Δx
where J is the mass movement per second, Δx is the length of the medium the substance is diffusing through (we are assuming a cylindrical container) and C1 and C2 are, of course, the concentrations of the two substances. J is measured in mass over seconds or moles per second, depending on the unit used to describe concentration.