ABSTRACT

There are four “excess” thermodynamic properties for real solutions – volume, enthalpy, entropy and free energy of mixing. The importance of the parameters is that they provide knowledge of the nature of the molecular interactions A-B and how the interaction changes with composition, on the nanoscale in the binary mixture, that are very difficult to measure directly or to predict. Non-volatile solutes produce predictable changes in the equilibrium properties of solvent A. These changes in the physical properties of solvent A are described as colligative properties, which depend only on the number of moles of solute particle B dissolved in the solvent A and not on the chemical identity of the solute. Thus, a colligative property equation can describe the effect for all solutes in a particular solvent. Non-volatile solutes are usually solid at room temperature and fall into one of two categories: electrolytes, which dissociate to produce ions in the solvent A, or non-electrolytes.