Generalized friction forces in electrochemical and gravitational non-equilibrium systems with or without temperature gradients

Abstract

[EN] A formalism is developed for the treatment of general, vectorial transport phenomena of the energetic quantities of Brønsted in nonelectrolyte or electrolyte systems with or without temperature gradients, gravitational or electric fields, and with or without a membrane matrix present. The treatment is based in the properties of so-called generalized friction forces between the streaming components and between these and the streaming entropy. The role of the proper form of the Gibbs¿Duhem equation in such systems is discussed in prolongation of the treatment of Sørensen and Compañ[Electrochim. Acta42, 639¿649 (1997)]. It is shown that the local dissipation may be expressed in the usual bilinear form of fluxes and forces, but this form is derived from the fact that the dissipation is the work performed against the generalized friction forces. The relation between the Galilei invariance and the noninvertibility of the phenomenological equations as well as the overall balance of the friction forces is stressed. The formalism is used to derive expressions for the electromotoric force in isothermal electrochemical cells with a membrane separator and gravitational forces included, for thermoosmotic effects and thermodiffusion of salts in membranes and for thermoelectromotive forces over membranes. Suitable ¿quantities of transport¿ are defined in nonisothermal systems. Using the ¿quasi-thermostatic method¿ of Helmholtz, Thomson and Brønsted and using the present formalism lead to the same results. Single ion activities cannot be found experimentally neither from isothermal nor from nonisothermal measurements of electromotive force.