Thermodynamics of lithium-isotope-exchange reactions. IV. Exchange between the isotopic metals and solid fluorides

This paper reports our results for the direct experimental determination of the equilibrium constant for the lithium-isotope-exchange reaction 7Li(s) + 6LiF(s) = 6Li(s) + 7LiF(s). This reaction was studied in electrochemical double cells without liquid junction of the type 7Li(s)|7LiF(s)|KBF4(pc)|6LiF(s)|6Li(s), where pc represents the solvent propylene carbonate. The experimental value of the equilibrium constant for this reaction is K = 1.10 ± 0.01 (296°K). We also report here our results for a complete Born-von Kármán lattice calculation of the equilibrium constant for the above reaction. The calculated result is K = 1.082 at 298.15°K. The above reaction exhibits the largest lithium isotope effect that has been found experimentally.