The CHESS model for calculating chemical equilibria in soils and solutions

This chapter describes a model for chemical equilibria in soils and solutions (the CHESS model) that can be used to assess reaction formulation in environmental chemistry research. The approach used in the CHESS model is similar to models such as MINEQL that are based on the tableau notation for describing chemical systems. A thermodynamic approach for modeling reactions between dissolved solutes and soil surfaces can be patterned after the approach used for solute-solute interactions. An equilibrium model capable of simulating soil surface reactions using a variety of formulations, and in a variety of experimental systems, can provide information necessary for evaluating the applicability of various equilibrium approaches. The CHESS model was designed to allow the user to evaluate alternative formulations for sorption reactions. Some of the formulations which have been used with the CHESS model are discussed for reactions involving sulfate adsorption and cation exchange.