A new approach to the analysis of absolute free energies, enthalpies and entropies of hydration of individual gaseous ions and absolute single-ion viscosity B-coefficients

Abstract

Least-squares analytical techniques are used to examine additivity relationships for combinedion thermodynamic data to effect appropriation into single-ion components for alkali-metal halide salts by employing Fajans' competition principle. Absolute free energies, enthalpies and entropies of hydration are derived leading to values of ΔH^⊖_hyd(ion)(g)/kJ mol^–1: Li⁺, –536.3; Na⁺, –420.8; K⁺, –337.1; Rb⁺, –312.5; Cs⁺, –287.3; F^–, –513.6; Cl^–, –362.8; Br^–, –331.8; I^–, –291.5; ΔG^⊖_hyd(ion)(g)/kJ mol^–1: Li⁺, –498.0; Na⁺, –392.2; K⁺, –319.2; Rb⁺, –297.4; Cs⁺, –274.3; F^–, –468.2; Cl^–, –336.0; Br^–, –309.8; I^–, –275.0; ΔS^⊖_hyd(ion)(g)/J K^–1 mol^–1: Li⁺, –128.5; Na⁺, –96.1; K⁺, –60.1; Rb⁺, –50.7; Cs⁺, –43.6; F^–, –151.8; Cl^–, –89.8; Br^–, –73.7; I^–, –55.2. The absolute enthalpy of the proton is assigned to be –1107 kJ mol^–1. For the viscosity B-coefficients the following absolute ion values are assigned for B(ion)/dm³ mol^–1: Li⁺, 0.136; Na⁺, 0.072; K⁺, –0.021; Rb⁺, –0.043; Cs⁺, –0.059; F^–, 0.133; Cl^–, 0.007; Br^–, –0.018; I^–, –0.055. The significant conclusion from these values is that the customary assumption, widely used in the literature, that B(K⁺)≈B(Cl^–) may not be correct and that the Krumgal'z assumption that B(Cs⁺)≈B(I^–), suggested in 1973, is more reliable in aqueous solution. We intend to examine this latter question further.