Standard thermodynamic functions of the gaseous actinyl ions MO n+2 and for their hydration

Abstract

The standard molar ideal gas thermodynamic functions of the singly and doubly charged uranyl, neptunyl, plutonyl and americyl ions MOⁿ⁺₂(n= 1 or 2) have been calculated from structural, and electronic and vibrational spectroscopic data. Estimates have been made for values not found in the literature. The heat capacity, entropy, enthalpy and Gibbs free energy are reported over the temperature range 100–1000 K. The values for 298.15 K have been combined with the standard partial molar entropies of these ions in aqueous solutions to yield the standard molar entropies of hydration. For the hexavalent uranyl ion data are also available for the standard partial molar heat capacity of the aqueous ion and the standard molar heat of formation of the gaseous ion, so that the corresponding quantities of hydration could be calculated. The thermodynamic functions of hydration are interpreted in terms of a model for the hydrated ions.