Selected thermodynamic functions of thionyl chloride

The compound thionyl chloride when heated above the region of 560[degrees]K will undergo dissociation to a measurable degree. The reaction 43OCl[lowered 2] = 3Cl[lowered 2]+23O[lowered 2]+S[lowered 2]Cl[lowered 2] is presumed to take place. In this investigation a carefully purified sample of thionyl chloride was prepared and was found to boil at 76.5[degrees]C. Samples of the thionyl chloride were heated in an all Pyrex apparatus and their pressures were measured with the aid of a Bourdon type sickle gauge. From those pressures it was possible to calculate the equilibrium constant at several temperatures. The equilibrium constant in turn made the calculation of [Delta]F[degrees] possible. The enthalpy change was determined by plotting the van't Hoff equation and measureing the slope of the line.