Thermodynamic Quantities for Reactions of Alkali Metaborate Monomer and Dimer Vaporss

概要

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Alkali metaborate monomer and dimer vapors have been studied thermodynamically, and these results have been compared with those for alkali halides. The ratios of mean dissociation energies for one M-BO2 bond in the M2(BO2)2(g) dimers to dissociation energies for one M-BO2 bond in the MBO2(g) monomers are almost constant for all the alkali metals (M) and an average value is 0.63±0.01. This value is just equal to the corresponding ratios for halides. For the dimerization reactions of MBO2(g), both free energies and enthalpies decrease in going from M=Li to M=Cs, while entropies are almost constant. A similar tendency can be seen in chlorides. For the alkali-alkali exchange reactions in the dimers, free energies, enthalpies, and entropies are very small for both metaborates and chlorides. Excess stabilities in the alkali-alkali mixed-dimer formations are explained from the correlation with the increases in the alkali cation-cation repulsion energies.