Nanochemical equilibrium involving a small number of molecules: a prediction of a distinct confinement effect

The equilibrium state of a reaction mixture comprised of a small number of molecules is modeled for three different nanoconfined systems. The issue is relevant to several advanced routes for the synthesis of encapsulated organic molecules, metallic or inorganic nanoclusters, and other nanoscale structures. Canonical-ensemble based formulations and computations predict for the equilibrated closed small systems significant deviations from the (macroscopic) thermodynamic limit. The effects include the enhancement/suppression of the equilibrium extent of the exothermic/endothermic model reactions, associated mainly with reduced numbers of mixed reactant-product microstates in the closed system. Fluctuations in the nanochemical reaction extent, which are found to be closely related to the stoichiometric coefficients, become more dominant for smaller systems and modify considerably the temperature dependence of the equilibrium constant.