The interaction of V2O5 with calcium oxide and calcium carbonate was studied by thermal analysis. The results indicated that the macrosuccession of the phase transformations in the systems CaO-V2O5 and CaCO3-V2O5 corresponds to an increasing calcium content in each successively formed calcium vanadate. Thermodynamical calculations carried out by methods available in the literature for determining the primary products and the succession of the subsequently formed products demonstrate that chemical reactions proceeding in the above systems are controlled by kinetic and not by thermodynamic factors.