Kinetics of Decomposition of Nitric Oxide at Elevated Temperatures. I. Rate Measurements in a Quartz Vessel

The rate of thermal decomposition of nitric oxide has been measured in a quartz vessel from 872 to 1275°K. The reaction follows a second-order rate law over the range of temperatures studied. Variations in the surface-to-volume ratio of the reaction vessel indicate the predominance of a heterogeneous mechanism at temperatures below 1000°K, whereas at higher temperatures a homogeneous mechanism prevails. The experimental data are interpreted on the basis of the relative contribution of the heterogeneous and homogeneous mechanisms to the over-all kinetics. Such an analysis explains the variation in effective activation energy with temperature from a value of 21.4 kcal below 1000°K to 82 kcal above 1600°K. An intermediate temperature region exists in which both mechanisms contribute an important part to the over-all rate.