Vapor Pressures and Vapor Thermodynamic Properties of Some Lithium and Magnesium Halides

Abstract

The vapor pressures of LiF, LiCl, MgF₂, and MgCl₂ have been measured by the torsion‐effusion method. The lithium halide vaporization data have been analyzed to yield heats of sublimation of monomer and dimer species which are consistent with available data on vapor composition, heats of dimerization, and the normal boiling points. Derived heats of sublimation of monomer and dimer at 298°K are 66.5 and 71.6 kcal/mole for LiF and 51.0 and 52.0 kcal/mole for LiCl, respectively. An analysis of the data obtained here and other vaporization data on the magnesium halides indicates that the available entropy and free‐energy functions for MgF₂(g) and MgCl₂(g) may be low by 4 to 5 cal/mole deg. Possible reasons for the discrepancy are discussed. The heats of sublimation of MgF₂(g) and MgCl₂(g) at 298°K are calculated to be 93 and 59 kcal/mole, respectively.