Is the Chemical Equilibrium-Constant always Constant ?
(Not for a Reaction-Mixture under Nano-Confinement !)

Chemical equilibrium involving a small number of molecules inside a confined nanospace can exhibit mixing-entropy related considerable deviations from the macroscopic thermodynamic limit. Thus, in the nanoscale range the "equilibrium constant" is system-size dependent, as was predicted for the first time in several of our works using statistical-mechanics and the lattice-gas model (e.g., ref.[1]). In particular, for exergonic addition and dimerization reactions a considerable shift of the bimolecular association extent towards product formation is expected as compared to only minor or even inverse effects in the case of endergonic reactions. The phenomena should be relevant to several advanced routes for the synthesis of encapsulated organic molecules, metallic or inorganic nanoclusters, as well as to reactions inside pores, droplets and nanoparticles. The effect was verified by a new analysis [2] of reported measurements concerning DNA hybridization inside confined nano-fabricated chambers. Thus, the DNA dissociation constant and extent are consistently diminished. This extra stabilization may have biological significance.

Nevertheless, it appears that a comprehensive recognition of the strict nano-confinement conditions for potentially practical implications, as well as full insight into the entropic origin and theoretical importance of the unique effect, are still lacking. Finally, modeling of Ir dimers preferential formation at the subsurface of Pd cuboctahedrons will be presented. Such phenomena are likely to affect catalytic properties of useful alloy nanoparticles.

[1] M. Polak and L. Rubinovich, Nano Letters 8, 3543, (2008).

[2] L. Rubinovich and M. Polak, Nano Letters 13, 2247, (2013).