Expressions for Enthalpies of Concurrent Polynuclear Complex Formation Reactions in Two-Phase Aqueous Systems

Abstract

The paper presents a new thermodynamic approach to studying polynuclear complex formation reactions in multicomponent two-phase systems, solid phase plus saturated aqueous solution, under real conditions. The quintessence of this developed approach consists in the thermodynamic analysis of concurrent reactions on the basis of the introduced notion of a generalized reaction equation. The formation of complex polynuclear species is characterized by certain peculiarities in the behavior of studied two-phase heterogeneous systems. The formation of polynuclear complexes of the metal ion with a complexing agent leads to expressions for the enthalpy ∆H and heat capacity ∆Cp as certain concentration functions, which are normative multipliers, referring these thermochemical quantities to one mole of the metal ion. It is shown that one of these functions, Φ, characterizes the degree of formation of polynuclear complexes. In the case of concurrent formation of mono- and polynuclear complexes, the derived expressions are useful in distinguishing separate contributions of individual complex formation reactions to the ∆H and ∆Cp of the overall process.