Determination of the absolute values of Gibbs energy of hydration or solvation ΔG~0_(abs)(M~+or X~-)_(hors) of monovalent (alkali metal and halide) ions and other thermodynamic parameters in aqueous and non-aqueous solvents using a single standard

摘要

Absolute values of Gibbs energy of hydration (h) or solvation (s) of alkali metal and halide ions ΔG~0_(abs)(M~+ or X~-)_(h or s) and other thermodynamic parameters in aqueous and non-aqueous solvents (methanol, ethanol, n-propanol, isopropanol, n-butanol, ethylene glycol, propylene carbonate (PC), N-methyl formamide (NMF), acetone, tetrahydrofuran (THF), 1,4-dioxan, acetonitrile) were determined directly using modified Born equation and a single standard state [i.e. ΔG~0 and ΔH~0 (but not ΔS~0) of H2 gas and other elements to be zero in their elementary standard states at 1 atm. pressure (1 bar) and 298 K]. The ΔH~0_(abs)(M~+ or X~-)_(h or s) and ΔG~0(M~+ or X~-)_(h or s) values are calculated considering ion-dipole, ion-quadrupole interactions and without considering the interaction terms. Very few data are available in non-aqueous solvents for comparison. Most of the single ion values (particularly for the anions) suffer from limitations associated with the erroneous principle of division of solvation energies ΔG~0_(h or s)(MX) or ΔH~0_(h or s)(MX) of electrolytes into single ion values. ΔG~0(M~+ or X~-)_h values determined using cluster-ion solvation data have also been presented. The values have been claimed to be most accurate in recent years. However, the method involves a number of assumptions of doubtful validity and the values cannot be regarded to be equivalent to ΔG~0(M~+ or X~-)_(h or s) determined by other workers using different methods. Coupling the values of ΔG~0(M~+ or X~-)_(h or s) and ΔH~0(M~+ or X~-)_(h or s) with ΔG~0(M~+ or X~-)_g and ΔH~0(M~+ or X~-)_g values in the gaseous state, ΔG~0(M~+ or X~-)_(water or org. solvent), ΔH~0(M~+ or X~-)_(water or org. solvent) and ΔS~0(M~+ or X~-)water or org. solvent [values in water and in organic solvents] are determined.