The kinetics of formation of sodium hexachlorozirconate from sodium chloride single crystals and zirconium tetrachloride vapor at about 600 Torr have been investigated by the weight-gain method. Analysis of the results showed the formation reaction to be diffusion controlled, with zirconium tetrachloride being the most probable diffusing species. The apparent energy of activation has been determined for this reaction from the variation of the rate constant with temperature, and it was found to be 12.3 ± 3 kcal/mole. The Arrhenius rate equation for the formation of Na2ZrCl6 from NaCl and ZrCl4 at 600 Torr pressure, in the temperature range 400 to 500 °C, is [Formula: see text]where the units of the parabolic rate constant, K, are (g(Na2ZrCl6))2 cm−4 h−1.