Kinetics of the Nitrous Oxide–Hydrogen Reaction

Abstract

The reaction of hydrogen with nitrous oxide was studied behind incident shock waves over the temperature range 1700°–2600°K. Experimentally, the concentration profiles of OH and the concentration of NO after the decomposition of N₂O were measured by uv absorption. The OH profiles have qualitatively similar features to those determined in the H₂–O₂ reaction. The concentration of NO after the disappearance of N₂O remains constant for several hundred microseconds. Interpretation of the experiments was based on a mechanism which contains the currently accepted data on the H₂–O₂ reaction and four additional reactions. Computer calculations show that the rate constants for the reaction $$\mathrm{O}+{\mathrm{N}}_2\mathrm{O}\to {\displaystyle {lim}^{k_3}}2\mathrm{NO}$$ as cited in the current literature are too low. The magnitude of k₃ determined in this work is consistent with published data on the reverse reaction, and $k_3{\text{\hspace{0.17em}=\hspace{0.17em}6.3\hspace{0.17em}×\hspace{0.17em}10}}^{14}\exp \text{(−\hspace{0.17em}26 700\hspace{0.17em}/\hspace{0.17em}RT)}{\mathrm{cm}}^3{\mathrm{mole}}^{\text{−1}}·{\sec }^{\text{−1}}$ is believed to be correct to within a factor of 3 between 1700° and 4000°K. The present investigation also permitted estimation of the constant for the reaction $$\mathrm{H}+{\mathrm{N}}_2\mathrm{O}\to {\displaystyle {lim}^{k_5}}\mathrm{OH}+{\mathrm{N}}_2.$$ If the literature rate constants for the H₂–O₂ system are assumed to be correct the best fit to our data is achieved with $k_5{\text{\hspace{0.17em}=\hspace{0.17em}4.0\hspace{0.17em}×\hspace{0.17em}10}}^{13}\exp \text{(−\hspace{0.17em}12 000\hspace{0.17em}/\hspace{0.17em}RT)}$ . However, a number of inconsistencies remain in the lower temperature range which cannot be reconciled within the framework of the assumed mechanism. These are similar to difficulties which were reported by others on the H₂–O₂ reaction.