Vapor composition and the thermodynamic parameters of lanthanum trichloride

The vapor composition over lanthanum trichloride was studied by high-temperature mass spectrometry. Monomeric LaCl 3 and dimeric La 2 Cl 6 molecules and Cl - , LaCl - 4 , and La 2 Cl - 7 ions were observed in saturated vapor at 937-1144 K. The partial pressures of vapor components were determined. The second and third laws of thermodynamics were used to calculate the enthalpies of sublimation Δ s H°(298.15 K) in the form of monomeric and dimeric molecules, 340 ′ 4 and 486 ′ 20 kJ/mol for LaCl 3 and La 2 Cl 6 , respectively. Ion-molecular equilibria including negative ions were studied, and the equilibrium constants, enthalpies of reactions, and enthalpies of formation Δ f H°(298. 15 K) of the molecules and ions were calculated, -737 ′ 5 (LaCl 3 ), -1668 ′ 20(La 2 Cl 6 ), -1266 ′ 19 (LaCl - 4 ), and -2244 ′ 30 (La 2 Cl - 7 ) kJ/mol.