Before any model is ready for use it must be verified. The verification step is greatly simplified if the model is constructed using conventional computational methods, notation, and units. This chapter reviews some procedures and conventions that are recommended for geochemical model construction.

Balancing chemical reactions

The first step in building a geochemical model is to write balanced equations that describe the governing chemical reactions. It is often possible to recognize these reactions based on past experiences, but when experience is lacking a general strategy is needed to identify these key reactions. The strategy should recognize that, with few exceptions, the key reactions involve the most abundant phases and chemical species. Creating a mineral inventory listing the possible hosts for the elements of interest is a first step toward selecting the solid phases to include in the model. Similarly, a chemical analysis of the aqueous phase can be used along with an aqueous speciation model to identify important aqueous species. The reactions among these mineral and aqueous species are expressed as balanced chemical reactions and these reactions become the basis for the subsequent model.