Improvements in Estimated Entropies and Related Thermodynamic Data for Aqueous Metal Ions

Abstract

New estimated standard entropies for some aqueous metal ions are obtained by taking account of magnetic and symmetry contributions. By combining them with an analysis of literature data, improved experimental and estimated values are derived for the standard enthalpies and Gibbs energies of formation of the aqueous ions of titanium, vanadium, chromium, manganese, cerium, and praseodymium. Separate entropy correlations are used for each primary coordination number, and the size dependence is represented by the reciprocal of the metal-oxygen distance in that coordination. The new scheme is consistent with recent work on the coordination of Hg(2+)(aq), Pb(2+)(aq), and tripositive rare earth ions. It differs from its predecessors in indicating a larger variation of the standard molar entropies of aqueous ions with coordination number. The value of S(Θ)(Be(2+), aq) is discussed in this context.