Читать книгу Geochemistry - William M. White - Страница 137

We emphasized at the beginning of the chapter the importance of choosing the components in a system. How well we choose components will make a difference to how easily we can solve a given problem. Morel and Hering (1993) suggested these rules for choosing components and species in aqueous systems:

1 All species should be expressible as stoichiometric functions of the components, the stoichiometry being defined by chemical reactions.

2 Each species has a unique stoichiometric expression as a function of the components.

3 H2O should always be chosen as a component.

4 H+ should always be chosen as a component.

H⁺ activity, or pH, is very often the critical variable, also called the master variable, in problems in natural waters. In addition, recall that we define the free energy of formation of H⁺ as 0. For these reasons, it is both convenient and important that H⁺ be chosen as a component.