Extents of reaction as supplementary constraints for Gibbs energy minimization
Pertti Koukkari, Peter Blomberg
Abstract
The stoichiometric conservation matrix C used in Gibbs energy minimization calculations conserves the molar amounts of the chemical elements of the multi-phase system. Supplementary reaction kinetic constraints can be included in min(G) by using additional massless components in the conservation matrix. A systematic method to incorporate such reaction constraints is based on row operations by which a coupled identity matrix I and a reaction matrix R is transformed into the augmented conservation matrix, C′. The reaction constraints then appear as well-defined components, based on measurable extents of slow reactions in the complex system, the incorporation of which allows for the calculation of the dynamical time evolution of the irreversible thermodynamic system. The non-zero affinities of the slow reactions are obtained as constraint potentials. The systematic I,R approach is explained by working through a few illustrative examples, showcasing the mechanics of applying it and the thermodynamic reasoning that accompanies it.