ABSTRACT
I. Introduction 225 A. Stoichiometry of chemical reactions 226
II. Surface Reactions 227 A. Mechanism of surface charging 228 B. Counterion association 230 C. Zero charge condition 232
III. Enthalpy of Surface Charging Reactions 233 A. Temperature dependency of the p.z.c. 233 B. Calorimetry 236 References 246
I. INTRODUCTION
The thermochemistry of surface reactions provides important information on the inter actions of ionic species at an interface. The thermodynamics of interfacial reactions is rigorously treated in Chapter 3 of this book. This chapter is devoted to the interpretation of experimental data, which is not simple. The results are usually expressed in an empirical way as “enthalpy per adsorbed amount,” and the mutual effects of adsorbed molecules are often neglected. In addition, an adsorption process may be accompanied by several others, either at the surface or in the bulk of the solution, so that “enthalpy per adsorbed amount” has no exact physical meaning. These problems are especially present in the case of surface-ionic interactions, since the binding of an ion to the surface influences all other equilibria at the interface through the electrostatic effects. For example, in the case of a metal oxide aqueous interface, several equilibria take place and influence each other. Thus the measured heat is not a consequence of one reaction only, so that the enthalpy of a particular surface reaction cannot be simply evaluated. Another problem is related to the separation of the electrostatic effects that is necessary in evaluation of the standard thermodynamic quantities.
