Chapter II - Solution thermodynamics — Use of the second and third derivatives of G

Abstract

This chapter follows the derivation of the second derivatives of G, partial molar quantities, and the third derivatives, intermolecular interaction functions. It demonstrates their actual power in elucidating the nature of mixing schemes or “solution structures,” evaluating these quantities for actual aqueous solutions. It begins with a discussion of gaseous mixtures and deriving their pressure using the Boyle-Charles law. Following this, it describes the Gibbs-Duhem relation. Furthermore, the study takes a turn to the discussion of vapor pressures. It demonstrates using an example, that in the state of equilibrium, the pressure of gas is equal to the pressure of liquid in an aqueous mixture. As a further discussion of the concept, it assumes that the gas phase mixture can be treated as an ideal mixture in comparison with the non-ideality of a liquid mixture. Since the density of gas is generally 1000-fold smaller than that of liquid, the intermolecular interactions in gas could be negligibly small in comparison with those in liquid. This assumption is demonstrated to be acceptable with an example. Furthermore, this chapter deals with Raoult’s law and Henry’s law, finally leading to the explanation of mixing–mixing entropy.