Introduction

We have now considered both ideal solution behavior and deviations from this, but in a rather generalized way, using activity coefficients. We now have to start to consider how to measure these things, and doing this means we have to consider partial molar properties in much more detail.

We start with a fairly detailed look at the volumetric properties of solutions, because these are the most intuitive. Partial molar properties of the other state variables are the same in principle, but become more complicated in the case of enthalpy measurements because of its relative nature. The Gibbs energy is also a relative property, but is treated in quite a different way.

Most of the material in this chapter is quite general, and can be applied to any kind of solution, although most of our examples are for aqueous solutions. The properties of electrolyte solutions introduce complications, discussed in Chapter 15. The properties of real gaseous solutions are often handled by “equations of state,” the subject of Chapter 13, and those of solid solutions have some unique aspects, discussed in Chapter 14.

Solution volumes

All real solutions are of course nonideal. Our discussion of their properties will be concerned for the most part with deviations from the properties of ideal solutions, whether Henryan or Raoultian.

Partial and apparent properties

The properties of a dissolved substance are described in terms of partial, apparent, and excess total or molar properties, so we begin by discussing these terms, using volume as an example.