20. Transport Phenomena

Diffusion can play an important role for the kinetics of chemical reactions in solutions. We use that as an opportunity to discuss this process of molecular motion more closely. The migration velocity is determined by a gradient of chemical potential and therefore eventually by a concentration gradient. This leads us to the quantitative description with the help of Fick’s law of diffusion. But not only matter can be transported from one place to another but also some other properties such as entropy or momentum. Entropy conduction is determined by the migration of entropy down a temperature gradient and viscosity by a migration of linear momentum down a velocity gradient. In order to carve out the commonalities and differences of the transport phenomena discussed, they are summed up in the last section and compared with the transport of electric charge, because the latter is the best known of these phenomena.