The low-temperature heat capacity and standard entropy of synthetic huttonite ThSiO4

The low-temperature heat capacity of synthetic huttonite ThSiO₄ has been measured from T = (2 to 300) K. The sample was synthesised successfully from SiO₂ and ThO₂ by solid-state reaction at T = 1873 K at atmospheric pressure. From the calorimetric results, the value for the standard entropy $S_{\text{m}}^{°}$ (ThSiO₄, huttonite, 298.15 K) = (104.3 ± 2.0) J · K^?1 · mol^?1 has been obtained. This value indicates that the entropy of reaction from SiO₂ and ThO₂ is negative, giving a positive entropy term (?T · Δ_rS) of the Gibbs free energy of reaction. The implications of this finding are discussed extensively.