Hydration of CN⁻, NO₂⁻, NO₃⁻, and OH⁻ in the Gas Phase

Abstract

By measuring the A − (H 2 O) n−1 + H 2 O = A − (H 2 O) n equilibria in the gas phase and their temperature dependence, the equilibrium constants and ΔH n , n–1 and ΔS n , n–1 for some of the hydrates of NO 2 − , NO 3 − , CN − , and OH − were determined. Available thermochemical data are used for the evaluation of the total heats of hydration of the above ions. The total heats of hydration were then compared with the ΔH 1,0 . Relative to the total hydration energies the ΔH 1,0 of the above ions were found larger than the ΔH 1,0 of the halide ions.An approximate linear correlation was found to exist between ΔH 1,0 of negative ions and the heterolytic bond dissociation energy D(A − –H + ). With this relationship independent estimates for the electron affinities of NO 2 and NO 3 could be obtained.The ΔH n , n–1 of OH − were found in essential agreement with earlier measurements from this laboratory and in disagreements with recent measurements (Friedman) which gave much higher values.