eng Science and Education Publishing World Journal of Chemical Education 2375-1657 2015-12-01 3 6 127 133 10.12691/wjce-3-6-1 WJCE2015361 article Juan José Baeza-Baeza juan.baeza@uv.es 1 Francisco Fernando Pérez-Pla 2 María Celia García-Álvarez-Coque 2 Departament de Química Analítica, Universitat de València, c/Dr. Moliner, Burjassot, Spain Institut de Ciencia dels Materials (ICMUV), c/Catedrático Beltrán, Paterna, Spain The use of computational software can greatly facilitate the teaching of chemical equilibria. It allows the treatment of complex problems without the need of simplifications, and the outcome of a very large number of calculations in a short time. Two practical examples of different complexity are proposed in this work to show the application of a general systematic approach for the numerical calculation of multi-equilibria problems, regardless of the number or types of equilibria involved. The method consists in writing down a system of non-linear equations formed by equilibrium constant expressions and the needed number of conservation balances so to match the number of chemical species involved. The exact solution of the system of non-linear equations describing the multiple equilibria is obtained by means of the fsolve tool of the open source software OCTAVE. The approach also allows multiple calculations by automatic changing of the initial conditions. The graphical representation of the concentration of chemical species is also possible as a function of selected variables, such as the initial concentration or the volume of a given reagent. http://pubs.sciepub.com/wjce/3/6/1/wjce-3-6-1.pdf chemical equilibrium multi-equilibria problems non-linear equations diprotic acid carbonate solubility; OCTAVE software