Thorium Monosulfide: Heat Capacity and Thermodynamic Properties from 1–350°K. Re‐evaluation of the Magnetic Entropy of Uranium Monosulfide

The heat capacity of thorium monosulfide was determined between 1 and 22°K by an isoperibol method and between 8 and 350°K by an adiabatic method. Below 4.2°K the heat capacity is represented by $C_P{\text{\hspace{0.17em}=\hspace{0.17em}3.70\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−3}}{\text{T\hspace{0.17em}+\hspace{0.17em}3.98\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−4}}{T}^3\mathrm{J}°{\mathrm{K}}^{\text{−1}}·{\mathrm{mole}}^{\text{−1}}$ , where the first term is the conduction‐electron contribution and the second term the lattice contribution to the heat capacity. Values for the thermodynamic quantities $C_P{\mathrm{°,\; S°,\; (H°\hspace{0.17em}-\hspace{0.17em}H}}_0\mathrm{°)\hspace{0.17em}/\hspace{0.17em}T}$ , and ${\mathrm{(G°\hspace{0.17em}-\hspace{0.17em}H}}_0\mathrm{°)\hspace{0.17em}/\hspace{0.17em}T}$ at 298.15°K are 47.72 ± 0.24, 69.81 ± 0.35, 32.60 ± 0.16, and − 37.21 ± 0.19 J°K⁻¹·mole⁻¹, respectively. The entropy of formation at 298.15°K is − 15.46 ± 0.47 J°K⁻¹·mole⁻¹, and an estimated value for the Gibbs energy of formation at 298.15°K is − 430 kJ mole⁻¹. The magnetic entropy of uranium monosulfide associated with the ferromagnetic transition at 180.1°K was previously estimated as 6.8 J°K⁻¹·mole⁻¹ but has been re‐evaluated as 8.8 ± 0.4 J°K⁻¹·mole⁻¹. The re‐evaluation was based upon a new estimate of the lattice heat capacity of uranium monosulfide from the heat capacity of thorium monosulfide and a corresponding‐states calculation. These calculations also lead to the conclusion that the coefficient $\gamma$ in the conduction‐electron contribution to the heat capacity of uranium monosulfide above the ferromagnetic transition is only 59% of the value near 0°K.