Fundamental thermodynamic equations are presented for anisotropic bodies with account for thermal effects. Definitions for Gibbs energy and partial molar quantities with respect to a direction chosen in an anisotropic phase, as well as expressions for the chemical potential tensor of an immobile component of a solid and for the chemical affinity tensor for a physicochemical process (including chemical reactions) in terms of the strain tensor variables and mixed variables including one component of the stress tensor are proposed. Conditions of stationary affinity and phase equilibrium are deduced. The mechanochemistry of polymorphous transformations is formulated for the cases of first- and second-order phase transitions.