Movement of particles from higher chemical potential to lower chemical potential (chemical potential can in most cases of diffusion be represented by a change in concentration). Diffusion, the spontaneous spreading of matter (particles), heat, or momentum, is one type of transport phenomena.
Because diffusion is thermally activated, coefficients for diffusion by a single mechanism at different temperatures may be described by an Arrhenius equation:
Data may be fit by a straight line on a graph of log D (m2/s) as a function of l/T (K-1). The resulting line has a slope of ΔH/(2.303R), where R is the gas constant (8.3143 J/mole K) and ΔH (J/mole) is the “Amount of energy that must be placed into a system to form an activated complex in a reaction. On an energy diagram, this is the difference in energy between the reactants and the transition state. The activation energy is often perceived as an energy barrier which must be overcome for.”
Some or all content above used with permission from J. H. Wittke.