The Equilibrium Dissociation and Thermodynamic Constants of Nitrosyl Chloride. Comparison with Spectroscopic Data

摘要

Careful measurements of the equilibrium dissociation of nitrosyl chloride into nitric oxide and chlorine have been made in the temperature range 100ndash;220deg;. Pressurehyphen;temperature measurements at 0deg;hyphen;100deg; on mixtures of nitrosyl chloride and nitric oxide were made and from them the second virial coefficients of nitrosyl chloride gas were calculated. These vary from mdash;389 cm3/mole at 0deg; to mdash;196 cm3/mole at 100deg;. The virial coefficients were used to correct the measured equilibrium constants to those for perfect gases. Equations for free energy, entropy and heat content changes accompanying the dissociation were derived as functions of the temperature. The experimentally found entropy changes for the reaction were found to be less than those calculated from spectroscopic data by 3.61plusmn;0.3 cal./deg. To attain agreement, the spectroscopic entropy of nitrosyl chloride must be increased by 1.8 cal./deg., and this was attained by assuming that an observed infrahyphen;red frequency at 923 cmhyphen;1is a combination, 633+290 cmhyphen;1. For the reaction 2NOCl(g) = 2NO(g)+Cl2(g), Dgr;Fdeg;298=9,720plusmn;60 cal., Dgr;Sdeg;298=28.0plusmn;0.5 cal./deg. Dgr;Hdeg;298=18,060plusmn;200 cal.Sdeg;298(NOCl)=63.0plusmn;0.3 cal./deg.