Standard molal Gibbs energy of formation and entropy data for aqueous uranium and plutonium ions in all oxidation states and their complexes with OH™, Cl™, F™, C032™, P043™, and SO,2' are critically reviewed. Selected values are used In a modified Criss-Cobble entropy extrapolation to derive self-consistent analytical expressions for the temperature dependence of the standard molal Gibbs energies of formation of 74 aqueous species and, hence, the Gibbs energy changes and equilibrium constants of their complexation and solubility reactions, from 25 to 200 °C.

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Heat capacities and densities of aqueous solutions containing mixtures of simple electrolytes, [NaCl(aq) + CaClz(aq)l, [NaCUaq) + MgCl~(aq)l, and [CaCldaq) + MgCldaq)], have been measured from 298.15 to 373.15 K a t 0.6 MPa. For each system, values were obtained for full ranges of mixture compositions for total ionic strengths of approximately 3 and 5 mol-kg-1. Measurements for NaCl(aq) (0.11-5.95 mol-kg-l), MgClz(aq) (0.44-5.19 mol-kg-l), and CaCldaq) (1.46-5.54 mol-kg-') are also reported. The measurements were done using a flow differential heat capacity calorimeter in series with a vibrating-tube densimeter. Values for the apparent molar heat capacities and volumes are reported and compared to literature values and to values predicted by both Young's rule and Pitzer's theory.

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