As a result of thermodynamic data accumulation, an expected topic for chemical thermodynamics arises based on the thermodynamic data known for separate reactions, to calculate the integral thermodynamic characteristics of the previously unstudied processes. The multi-component heterogeneous system is formulated herein as biphasic system “precipitate (solid phase) - solution (liquid phase)”, in which a series of simultaneous reactions occur and the contribution of each depends on the chemical composition of the system, that is the ratio of the concentrations of the constituent components [1]. In this regard, an increased interest acquires the direct and indirect problems of the chemical thermodynamics in the heterogeneous multicomponent systems. In this context, the direct problem consists in calculating the thermodynamic functions of the overall process based on the thermodynamic characteristics of the particular reactions. The indirect problem is to calculate the thermodynamic characteristics of separate reactions based from the overall functions. On the other hand, the practical importance of buffer systems, as well as the need for focused search and the creation of new perspective buffer systems, have made the necessity to develop quantitative principles of the theory of buffering properties of multicomponent heterogeneous systems. The paper presents a new thermodynamic approach to the study of complex chemical equilibria in real conditions, taking into account the complex formation reactions in multicomponent heterogeneous systems. Its quintessence consists in the thermodynamic analysis of the conditions of various processes on the basis of their total thermodynamic characteristics. In the case of taking place of reactions of complex formation, hydrolysis and protonation in heterogeneous multicomponent systems, the total change of Gibbs energy cannot be presented as a sum of contributions of several separate reactions [2]. Original methods for determining such thermodynamic characteristics as the solubility and solubility product, as well as the stability constant of chemical compounds of the arbitrary composition in the heterogeneous multicomponent systems are also described. The quintessence of the elaborated formal thermodynamic approach consists in the analysis of the conditions of different processes based on the overall thermodynamic characteristics. The authors prove that in the case of the multicomponent heterogeneous complexation complexation reactions, the total Gibbs energy variation cannot be presented as a sum of the contributions of separate reactions. The calculation of the global Gibbs energy variation of complex chemical processes allows determination of the thermodynamic stability domains of solid phases, the direction and optimum conditions for chemical processes under conditions close to the real ones.