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

Abstract

Careful measurements of the equilibrium dissociation of nitrosyl chloride into nitric oxide and chlorine have been made in the temperature range 100–220°. Pressure‐temperature measurements at 0°‐100° 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 —389 cm³/mole at 0° to —196 cm³/mole at 100°. 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 3.61±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 infra‐red frequency at 923 cm^‐1 is a combination, 633+290 cm^‐1. For the reaction 2NOCl(g) = 2NO(g)+Cl₂(g), ΔF°₂₉₈=9,720±60 cal., ΔS°₂₉₈=28.0±0.5 cal./deg. ΔH°₂₉₈=18,060±200 cal. S°₂₉₈(NOCl)=63.0±0.3 cal./deg.