JESS, a Joint Expert Speciation System – VI: thermodynamically-consistent standard Gibbs energies of reaction for aqueous solutions

Abstract

Spanning all available combinations of more than 50 000 chemical species pertinent to aqueous solutions at 25 °C, a comprehensive set of reliable, thermodynamically-consistent standard Gibbs energies of reaction and their corresponding equilibrium constants is derived. The number and type of species that can be assessed for consistency is greatly expanded by abandoning conventional use of the chemical elements as the basis set. Using reaction data previously accumulated from the literature for almost 80 000 chemical reactions, equilibrium constants are automatically obtained (by extrapolation to standard conditions as necessary) and brought into thermodynamic consistency by a large-scale ordered Gaussian elimination process, yielding over 2500 basis species and the relative standard Gibbs energies for all other chemical species in known equilibrium with them. This allows the Gibbs energy difference for any relevant reaction to be calculated by summation. Strategies have been developed to ensure the process is dependable, scalable and sustainable. A new hazard with the averaging of thermodynamic parameters is identified. The results, which are openly available on-line, are in good accord with authoritative sources such as the U.S. National Institute of Standards and Technology (NIST) Thermodynamic Web-book and the Chemical Thermodynamics Series from the OECD Nuclear Energy Agency (NEA) but are far more extensive, including for the first time many analytical chelating agents and their metal complexes.