An equilibrium simulator for multiphase equilibria based on the extent of reaction and Newton-Raphson method with globally convergent strategy (SEQEx2)

An algorithm for simulation of chemical equilibrium was developed. The method is based on the extent of reaction instead of the mass balance, which is currently used in other programs. This feature, besides the globally convergent strategy applied in the Newton-Raphson method, allows to carry out simulations without a good approximation for the initial concentrations. The program SEQEx2, implemented with this algorithm, has been applied to systems with any kind of reaction (neutralization, precipitation, complexation, and oxidation/reduction). Two examples are shown. The simulation of calcium carbonate and water in contact with the atmosphere consumes 5 s in a 486DX2 66 MHz. The simulation of a conductometric titration of acetic and hydrochloric acids consumes 55 s for 601 additions of sodium hydroxide solution.