We have followed theoretically the local and global rates of decomposition, in aqueous solution, of a simple dimer A2 inside an upright cylindrical container with perfectly thermally conducting walls maintained at the initial temperature of the reactants. Computational fluid dynamics modelling, using the finite-volume method, indicates that the net reaction progresses significantly faster in the presence of gravity than in its absence. This accelerated rate of dimer decomposition in the presence of gravity is attributed to the effects of thermal convection currents that develop inside the walls of the vessel as a direct consequence of the reaction endothermicity. These convection currents cause more rapid heat transfer to the reaction vessel and are absent under conditions of zero gravity. The influence of natural convection on the spatiotemporal distributions of the product species and of temperature is also illustrated in this article.