A new estimation of the lattice energies of the ammonium halides and the proton affinity of gaseous ammonia

A linear relationship between the viscosity B-coefficient of the Jones-Dole equation for aqueous solutions of certain alkali metal salts and the enthalpy of hydration of the gaseous monatomic constituent ions has been established. The assumption that a similar rectilinear law applies to ammonium halides appears justified and the enthalpies of solution of NH4 +(g)+X-(g) have been estimated and used to obtain magnitudes for the lattice energies of NH4X(c) [X=F, Cl, Br, I]. In conjunction with experimental thermochemical data, the latter yield consistent results for the proton affinity of ammonia ΔH 1 ⊖=860·5±2·0 kJ mol-1 (298·15 K). The lattice energies of the salts are, (in kJ mol-1) 834 (NH4F), 708 (NH4Cl), 682 (NH4Br) and 637(NH4I).