Experimental heat capacities of LaNi5, α-LaNi5H0.36, and β-LaNi5H6.39 from 5 to 300 °K. Thermodynamic properties of the LaNi5–H2 system

Abstract

The heat capacities of LaNi5, α‐LaNi5H0.36, and β‐LaNi5H6.39 were measured from 5 to 300 °K, and in the case of LaNi5 also from 300 to 350 °K. Various special techniques and unusual circumstances involved in the measurements and calculations are described. A slight enhancement of the heat capacity of β‐LaNi5H6.39 was observed in the temperature range 120 to 160 °K. The standard entropies of LaNi5, α‐LaNi5H0.36, and β‐LaNi5H6.39 at 298.15 °K were found to be 209.9±0.5, 214.1 ±0.5, and 271.7±0.7 J °K−1 mole−1, respectively. These results together with other thermochemical data were used to calculate the entropy and enthalpy of formation of β‐LaNi5H6.39 at 298.15 °K. The partial molar entropy of hydrogen in β‐LaNi5H6.39 was derived from our results and used to estimate the configurational entropy at 298.15 °K.