Thermodynamics of Lithium Isotope Exchange Reactions. II. Electrochemical Investigations in Diglyme and Propylene Carbonate

This paper reports our final results for the direct experimental determination of the equilibrium constants for the lithium isotope exchange reactions Li7(s)+6LiBr(digl)=6Li(s)+7LiBr(digl) Li7(s)+6Li+(PC)=6Li(s)+7Li+(PC)involving the solvents diglyme (digl, ε=7.2) and propylene carbonate (PC, ε=65.5). These reactions were studied in electrochemical double cells without liquid junction. The experimentally determined values of the equilibrium constants at 296.6°K are K1=1.035± 0.007 and K2=1.030± 0.005. The experimental values of K1 and K2 are compared with values calculated from statistical thermodynamic theory for various model reactions. A Born—von Kármán lattice calculation has been carried out for the isotopic lithium metals.