Temperature-driven mass, charge and heat transfer in terms of physicochemical potential and Einstein's mobility

Abstract

Unified description of mass, charge and heat transport in a solution in the presence of temperature gradient is suggested. The description is based on the idea that the rate of mass transport is proportional to the gradient of physicochemical potential, which is a more general function than electrochemical potential and includes the product of molar entropy and temperature. The proportionality coefficient is the product of Einstein's mobility and concentration. The approach explains the dependence of the Soret coefficient on concentration, molar entropy, and temperature. It also explains the reciprocal process (Dufour effect) and temperature-induced charge separation (Seebeck effect). In addition to usual reciprocal relation L 21=L 12 it gives the relation of different phenomenological coefficients of the Onsager description. In its turn, description of heat transport driven in opposite directions by concentration, pressure, and voltage gives classic equilibrium relations for mass transport.