Thermodynamics of solubility

Dixon, J. and Johnston, K. (1991) Molecular thermodynamics of solubilities in gas antisolvent crystallization. AIChE Journal, 37 (10), 1441-1449. 

If any three of the four reactions can be measured or calculated, the fourth can be found by completing the cycle. It has been possible to estimate the solvation effects of many ions by comparing similar measurements on a number of different compounds. Naturally, the entropy of solvation also needs to be included as part of the thermodynamics of solubility. 

In this chapter, the solubility phenomenon will be developed using fundamental theories. The basic thermodynamics of solubility reveals the relation between solubility, and the nature of the solute and the solvent, which facilitates an estimation of solubility using a limited amount of information. Solubility-related issues, such as the solubility of polymorphs, hydrates, solvates, and amorphous materials, are included in this chapter. In addition, dissolution rate phenomena will also be discussed, as these relate to the kinetics of solubility. A discussion of empirical methods for the measurement of solubility is outside the scope of this chapter, but is reviewed elsewhere (Grant and Higuchi, 1990 Grant and Brittain, 1995). 

In order to understand the thermodynamics of solubility, it is appropriate to begin with a simplihed model of solution, namely that of an ideal solution. An ideal solution is dehned as one where the activity coefficient of all components in the solution equals one. Under these stipulations, the activity of the dissolved solute, the activity of the solid, and the molar solubility of the dissolved solute would be equal. 

Thermodynamics of Solubility Mathematics of Diffusion Factors Affecting Solubility and Transport Crystallinity, Fillers, and Morphology Temperature and Transitions Penetrant Size... 

Now that we have a basic understanding of solvents and solutes, let s examine the thermodynamics of solubility in more detail. The concepts involved lead directly to the thermodynamics of reactions. The second section of this book delves into the kinetics and mechanisms of organic transformations, which are highly dependent upon the nature of the solvent and the reactants. Hence, many of the topics discussed above will be revisited in these discussions. However, because the thermodynamics of solutions affects reactions and molecular recognition (the topic of the next chapter), it makes sense to discuss the thermodynamics of reactions here also. Therefore, in this section we explore the thermodynamic driving force for solubility and chemical reactions. 

Although the thermodynamics of solubility are rather more complex than this (involving a consideration of entropy changes as described in Chapter 15), this simple rule of thumb often helps us to account for patterns in solubility. It can be summarized in the phrase like dissolves like . 

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