Equilibrium pressure measurements in the Li-N-H system by static manometric method

The equilibrium pressure over the phase mixture (Li2NH + LiNH2 + LiH) was measured from 343 to 683 K by static manometric method. The plot of ln (peq/p0) versus (1/T) showed three distinct temperature regions with different slopes. Analysis of the equilibrium gas composition in each temperature regions revealed that the equilibrium gas is a mixture of H2, NH3 and N2 below 443 K whereas above 443 K, the equilibrium gas is mainly H2. The enthalpy and entropy of the reaction of H2 with Li2NH to form LiNH2 and LiH are found to be −55.0 ± 1.3 kJ∙mol−1 and −86 ± 2 J∙K−1∙mol−1, respectively at 523 K, where LiNH2 exists in the solid state and −18.5 ± 0.5 kJ∙mol−1 and −26 ± 1 J∙K−1∙mol−1, respectively at 658 K, where LiNH2 exists in the liquid state. The enthalpy and entropy of melting of solid LiNH2 are calculated as 36.5 ± 1.4 kJ∙mol−1 and 60 ± 2 J∙K−1∙mol−1, respectively.