An algorithm for computation of simultaneous chemical and phase equilibrium in homogeneous as well as in heterogeneous liquid mixtures has been developed. It is based on the rigorous tangent plane stability test performed in transformed coordinates. The coordinates make it possible to represent phase equilibrium in reactive systems in a similar way as for non-reactive mixtures. Therefore, the reactive phase diagrams look similar to the non-reactive ones and geometric design procedures for non-reactive heterogeneous distillation columns can be extend to reactive systems. A detailed algorithm for design of a reactive distillation column with top decanter is presented.