A non-ideal solution is a solution that does not abide to the rules of an ideal solution where the interactions between the molecules are identical (or very close) to the interactions between molecules of different components. That is, there is no forces acting between the components: no Van-der-Waals nor any Coulomb forces. We assume ideal properties for dilute solutions. Activities and their Effects on Equilibria Activity is a measure of the “effective concentration” of a species in a mixture, in the sense that the species' chemical potential depends on the activity of a real solution in the same way that it would depend on concentration for an ideal solution. By convention, activity is treated as a dimensionless quantity, although its value depends on customary choices of standard state for the species. The activity of pure substances in condensed phases (solid or liquids) is normally taken as 1. Activity Activity is a measure of the effective concentration of a species under non-ideal (e.g., concentrated) conditions. This determines the real chemical potential for a real solution rather than an ideal one. Azeotropes An azeotrope is a mixture that exhibits the same concentration in the vapor phase and the liquid phase. This is in contrast to ideal solutions with one component typically more volatile than the other; this is how we use distillation to separate materials. If the mixture forms an azeotrope, the vapor and the liquid concentrations are the same, which preventing separation via this approach. Debye-Hückel Theory The Debye-Hückel theory of electrolytes is based on three assumptions of how ions act in solution: (1) Electrolytes completely dissociate into ions in solution (2) Solutions of Electrolytes are very dilute, on the order of 0.01 M and (3) Each ion is surrounded by ions of the opposite charge, on average. Introduction to Non-ideal Solutions A non-ideal solution is a solution that does not abide to the rules of an ideal solution where the interactions between the molecules are identical (or very close) to the interactions between molecules of different components. That is, there is no forces acting between the components: no Van-der-Waals nor any Coulomb forces. We assume ideal properties for dilute solutions. Template:HideTOC