<P> Consider two systems; S and S at the same temperature and capable of exchanging particles . If there is a change in the potential energy of a system; for example μ> μ (μ is Chemical potential) an energy flow will occur from S to S, because nature always prefers low energy and maximum entropy . </P> <P> Molecular diffusion is typically described mathematically using Fick's laws of diffusion . </P> <P> Diffusion is of fundamental importance in many disciplines of physics, chemistry, and biology . Some example applications of diffusion: </P> <Ul> <Li> Sintering to produce solid materials (powder metallurgy, production of ceramics) </Li> <Li> Chemical reactor design </Li> <Li> Catalyst design in chemical industry </Li> <Li> Steel can be diffused (e.g., with carbon or nitrogen) to modify its properties </Li> <Li> Doping during production of semiconductors . </Li> </Ul>

The spreading out of molecules in air from a center of concentration is caused by