Thermodynamic Modeling of Aqueous Electrolyte Systems: Current Status

The current status of thermodynamic modeling in aqueous chemistry is reviewed. A number of recent developments hold considerable promise, but these need to be weighed against ongoing difficulties with existing theoretical modeling frameworks. Some key issues are identified and discussed. These include long-standing difficulties in choosing the right program code, in comparing alternatives objectively, in implementing models as published, and in wasting effort on numerous proposed "modifications" and/or "improvements". There needs to be greater awareness of the major limitations that such assorted variations in modeling functions imply for practical thermodynamic modeling purposes. They typically lack proper substantiation, fail to distinguish between cause and effect, and are presented in ways that all-too-often cannot be falsified. Numerical correlations in particular permit overoptimistic assertions based only on "satisfactory" fits, neglecting the dictum that regression analyses can be used to discredit hypotheses but not to prove them. The risks of "model tuning" should always be acknowledged and minimized. Recognition of the uncertainties in data that have not been confirmed by independent measurement needs to be redoubled. Modeling frameworks incapable of explicit trace activity coefficient prediction should no longer be regarded as credible. The current modeling paradigm evidently has to be reassessed, hopefully to find better ways forward, including new protocols which command sufficient support to warrant IUPAC endorsement.