1890
T. K. WIEWIOROWSKI, A. PARTHASARATHY, AND B. L. SLATEN
Molten Sulfur Chemistry.
V.
Kinetics of Chemical
Equilibration in Pure Liquid Sulfur by T. K. Wiewiorowski, A. Parthasarathy, and B. L. Slaten Freeport Sulphur Companu, Belle Chasse, Louisiana
(Received December 80,1967)
The rate at which liquid octatomic sulfur rings, S8R, react to reach ring-chain equilibrium was investigated. Experimentally, this involved a study of the effect of temperature and time on the freezing point of liquid sulfur initially consisting only of octatomic sulfur rings. From the rate at which the freezing point depression occurred in the system, the reaction rate constant of chain formation was calculated. The temperature dependence of this rate constant is thermodynamically interpreted in terms of the dissociation energy of a sulfur-sulfur bond in octatomic sulfur, AH = 32 kcal/mole.
Introduction It is well known that the freezing point of liquid sulfur is lower than the melting point of monoclinic sulfur. This phenomenon has been experimentally observed by Smith' in 1903 and interpreted by Schenk and Thummler2 in terms of octatomic chain formationin the sulfur melt. Recently, this behavior was rationalized from the thermodynamic point of view by the theory of acid-base (ring-chain) equilibria in liquid sulfur.3 Although the effect of temperature on the freezing point depression of liquid sulfur has been studied to some extent, the kinetic aspect of this phenomenon has not been previously investigated. In the present study, the effect of time and temperature on the freezing point of pure liquid sulfur was studied in an effort to gain further understanding of the unusual physicochemical behavior of the system.
Experimental Section The sulfur used in this investigation was purified by the method of Bacon and Fanelli4and preconditioned at 95" to ensure complete conversion to octatomic rings. Samples of this sulfur (approximately 10 g) were placed in 5 X 0.5-in. test tubes. The test tubes were immersed in constant temperature oil baths maintained a t 130, 140, and 150" for a specified period of time. After the heating period, each test tube was removed from its oil bath and allowed to cool. Temperature measurements were made by means of a chromelalumel thermocouple inserted in the sample and connected to a millivolt recorder. To minimize supercooling, the melt was vigorously agitated. The temperature at which the first crystals were visually observed in the system was noted. There producibility of the data obtained in this manner was 50.2". The experimental results are condensed in Table I.
Discussion Thermodynamic considerations indicate that the freezing point of any pure solvent can be lowered by The Journal of Physical Chemistry
dissolving in it another component. The freezing point depression and the concentration of the solvent are related by the equation
where N is the mole fraction of pure solvent, AHf is the molar heat of fusion of the solvent, 2'0 is the freezing point of pure solvent in deg I 2) are shown to be in error. Rather an equilibrium M 2 2 + e 2MZ+ 2e- is indicated as proposed earlier in connection with electrical conductance measurements.
+
The following is part of an account of the extension of our general study on mixtures of the electropositive metals with their molten halides2to many of the alkaline earth metal-alkaline earth halide systems. Measurements of the electrical conductance carried out in parallel with the phase equilibrium studies have been discussed earlier.3 In the alkali metal-metal halide systems, miscibility of the metal with the salt had been found to increase with the atomic number, or the size, of either the metal or the halide ion, Le., apparently with the simultaneous decrease in the cohesive, or interionic, forces in both components.2 It was of interest to ascertain that this was indeed a general trend for this type of metal-salt miscibility by measurements on alkaline earth systems. The Journal of Phyaical Chemistry
Reported consolute temperatures, taken as a measure of miscibility, namely,
