engleski

Standard States and Activity Coefficients of Interfacial Species

Standard states of species at solid - liquid interface was analyzed in the same way as for other thermodynamic systems such as liquid or solid mixtures, gaseous phase and solutions. Accordingly, standard states of interfacial species are described by two characteristics ; the first one is composition and the second one is ideality. It is proposed to define standard composition on the basis of surface coverage or surface concentration. The ideal state of interfacial species were taken to be at the zero electrostatic potential and deviation from ideality was described by means of activity coefficients. Activity coefficients were derived for interfacial species charged due to the interaction with potential determining ions and for interfacial ion pairs. The presented approach was demonstrated on the example of the "2-pK" mechanism of surface complexation model and may be applied to any assumed mechanism of interfacial reactions. The derived thermodynamic equilibrium constants correspond to classical "intrinsic equilibrium constants".

standard state; activity coefficient; interface; surface complexation; site binding

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