Simplified theory of diffusion of mixed electrolytes with simultaneous chemical reactions. Application to glycine + HCl + H2O mixtures

Abstract

Expressions are obtained by non-equilibrium thermodynamics for the diffusion coefficients and Onsager transport coefficients of multicomponent electrolytes with chemical reactions. The results apply to isothermal systems with arbitrary numbers of electrolytes and chemical reactions, provided the rates of the reactions are rapid enough to guarantee local equilibrium. A procedure analogous to the Nernst–Hartley method is proposed for the estimation of transport coefficients of complex electrolyte mixtures from binary data. The procedure allows coupled transport of ions to be analysed in terms of electrostatic and chemical interactions between solute flows. For purposes of illustration, data available in the literature are used to predict ternary diffusion in glycine + HCl + H₂O mixtures. Diffusion in this system is strongly coupled by the protonation of the glycine zwitterion by HCl and by the electric field produced by diffusion of the ionic species.