Multicomponent equilibrium models for aqueous salt solutions have been developed With the novel ChemSheet program. The calculations are based on the minimization of the Gibbs free energy of the reaction mixtures. For the excess Gibbs energies of the solute species, the Pitzer interaction model with temperature-dependent parameters was used. The results of the ChemSheet multiphase calculations have been verified with experimental or reference data. With the presented modeling technique, reaction kinetics can also be taken into account for specific systems using the Gibbs energy approach. These methods have been applied to the aqueous chemistry of calcium carbonate and sulfate in the wet-end solutions of papermaking. ChemSheet models are applicable in spreadsheets and can be customized for the needs of an industrial user.