David M. Mason

Thermodynamic Properties of the Titanium Chlorides

From a series of ten different experiments performed at this laboratory and from experiments reported elsewhere, the following thermodynamic properties have been obtained (ΔHf298 in kcal/mole and S°298 in cal/°C/mole): TiCl4(l), ΔHf298=—191.2; TiCl4(g), ΔHf298=—181.6; TiCl3(s), ΔHf298=—170.7, S°298 =34.4; TiCl3(g), ΔHf298=—128.7, S°298=74.9; TiCl2(s), ΔHf298=—120.6, S°298=24.7; TiCl2(g), ΔHf298 =—69.4, S°298=65.9. A theoretical value for S°298 of 56.1 was calculated for TiCl(g). Estimated values for the Cp of these compounds are also included.

Calorimetric Determination of Heats of Formation of Titanium Chlorides

The heats of formation of TiCl4(l), TiCl3(s), and TiCl2(s) were determined by chlorinating Ti, TiCl3(s), and TiCl2(s), respectively, in a nickel‐bomb calorimeter to give TiCl4(l). The directly measured heat of chlorination at 25° of Ti is —190.0±0.4, of TiCl3(s) is 20.9±0.1, and of TiCl2(s) is 69.9±0.8 kcal/mole—1. Relative to a value for the heat of formation of TiCl4(l) of —190.0±0.4, the corresponding values for the heats of formation of TiCl3(s) and TiCl2(s) are —169.1±0.4 and —120.1±0.8 kcal/mole—1, respectively.

Measurement of Equilibrium of the Reaction: TiCl3(s)+HCl(g) ⇋TiCl4(g)+1/2H2(g)

Equilibrium in the TiCl3(s)–HCl(g) system was studied in the temperature range 350 to 475°C by measuring the total pressure in an isochoric vessel. The equilibrium data for the above reaction in this temperature range is given by log10K (atmos) = (—2.27×103/T)+1.82. From these data, the enthalpy and entropy of reaction at the average temperature of about 690°K are 10.4±0.4 kcal and 17.5±0.5 cal/deg, respectively. From an estimated value for the ΔCp of reaction, the enthalpy and entropy of reaction at 25°C are estimated to be 12.7±1.0 kcal and 22.5±2.0 cal/deg, respectively. The difference between the enthalpies of formation of TiCl3(s) and TiCl4(l) is 19.0±1.0 kcal/mole—1 at 25°C. The equilibrium is shifted toward TiCl4(g) and H2(g) with increase in temperature, and 25°C the reduction of TiCl4(g) by H2(g) to give TiCl3(s) is nearly complete, although the rate of the reaction is very low.