Thermodynamics of Mixtures (Multicomponent Systems)

Abstract

This is the central chapter of the book which is not only concerning the arrangements of the eleven chapters but also has the key role from the point of view of chemical thermodynamics. The reader finds a meticulously explained description of the basic thermodynamic characteristics of multicomponent systems which are of paramount importance in chemistry. Though the composition variable is explicitly present in the formalism from the beginning of the book, and the chemical potential is also introduced at an early stage, the complicated dependence of the chemical potential on the composition of various mixtures needs a special approach. The most common and useful thermodynamic function in chemical applications is the chemical potential – mainly as a function of pressure and temperature – thus the chapter concentrates on the dependence on composition of the chemical potential when the other variables are pressure and temperature. Widely used partial molar quantities are also introduced at the beginning of the chapter, with a short discussion of their experimental determination. The thermodynamic discussion of mixtures begins with the basic formalism on the example of a mixture of ideal gases, and then this description – the ideal mixture formalism – is extended for use in the case of real mixtures. In discussing real mixtures, emphasize is on the precise treatment of various activities and reference states or standard states related to the relative activities. The definition of the activity coefficient is based on excess quantities. A detailed comparison and interrelation of different activities is also shown, including the case of ideal dilute solutions. Thermodynamic properties of real solutions are deduced from the chemical potential function.