Partial molal entropy and heat capacity of the aqueous thorium(IV) ion. Thermochemistry of thorium nitrate pentahydrate

Th(NO3)4.5H2O(c) was prepared in high purity and its enthalpy of solution was measured in 0.01 M HClO4 at 15, 25, and 350C, using a calorimeter sensitive to 5 x 10-6K. These measurements are combined with recent literature data to derive anti S0(Th4+, aq) = -424 +- 4 J mol-1 K-1, anti C0/sub p2/(Th4+, aq) = -1 +- 11 J mol-1 K-1, and ΔH0/sub f/[Th(NO3)4.5H2O, c] = -3009 +- 4 kJ mol-1 at 298.150K. Anti S0 and anti C0/sub p2/ are interpreted by comparison with other monatomic ions, using appropriate semiempirical equations