Ionization equilibria at high pressure

The equilibria of reactions forming or dissipating ions or those which change the charge of existing ions, such as the dissociation of acids or dissolving of salts, depend on pressure as equilibrium constants(1) and activity coefficients are both functions of pressure. In particular, acid-base reactions which are responsible for the pH value of the medium and for reactions of proteins play an important role in high-pressure microbiology and food science. To understand more about such reactions it is important to understand the pressure behaviour of such reactions. In this study the background and the most important methods from previous studies to determine this pressure behaviour are introduced and discussed, specifically for reactions affecting the pH value. A comprehensive theory has not yet been proposed, but some models described in the literature show adequate agreement with existing measurements and can be used to interpret experimental results. The reason for the changes of equilibrium constants with pressure and the basis for the calculation is the volume change accompanying a reaction. This volume change is caused mainly by the electrostatic interaction between an ion and surrounding water.