The objective of this work is to present a procedure for the calculation of chemical and phase equilibrium (CPE) in multicomponent mixtures subject to the effect of gravitational fields. The specifications are the total volume, initial number of moles of each species and temperature. The problem is formulated as the minimization of a modified form of the Helmholtz function that contains a term to account for the potential energy. To solve this problem, the system is divided into layers. It is assumed that each of these layers is a homogeneous part of the system, and that each phase occupies a specified number of layers. Layers in the same phase are assumed to have the same size whereas those in different phases typically have different sizes. In the minimization of the modified Helmholtz function, the independent variables are the volume fraction of each phase (thereby defining the location of the interfaces) and the number of moles of each species in each layer, taking into account the possibility of chemical reactions. The procedure is used to calculate density and pressure profiles with height for pure fluids close the critical point and composition profiles for reactive and non-reactive mixtures.