Kinetics of the Thermal Dissociation of N2F4 in Shock Waves

The equilibrium dissociation of N₂F₄⇌2NF₂ was studied in shock waves, yielding an equilibrium constant identical to those obtained previously in static measurements. The thermal dissociation rate for N₂F₄ diluted with argon, helium, and SF₆ was studied between 350° and 450° at total pressures of 0.58–2.7 atm. The reaction $$\mathrm{M}\mathrm{\hspace{0.17em}+\hspace{0.17em}}{\mathrm{N}}_2{\mathrm{F}}_4\rightleftharpoons {\displaystyle {lim}^{k_M}}\mathrm{M}\text{\hspace{0.17em}+\hspace{0.17em}2}{\mathrm{NF}}_2$$ was found to be first order in M and first order in N₂F₄, indicating a bimolecular mechanism. The rate constant for argon could be expressed either by $$k_{\mathrm{Ar}}{\text{\hspace{0.17em}=\hspace{0.17em}1.5\hspace{0.17em}×\hspace{0.17em}10}}^{12}{T}^{\text{0.5}}\exp \text{(\hspace{0.17em}−\hspace{0.17em}15 200\hspace{0.17em}/\hspace{0.17em}RT)}\mathrm{liter}/\mathrm{mole·sec}$$ or $$k_{\mathrm{Ar}}{\text{\hspace{0.17em}=\hspace{0.17em}3.0\hspace{0.17em}×\hspace{0.17em}10.T}}^{\text{0.5}}{\mathrm{(E}}_0{\mathrm{\hspace{0.17em}/\hspace{0.17em}RT)}}^{\text{4.0}}\exp {\mathrm{(\hspace{0.17em}-\hspace{0.17em}E}}_0\mathrm{\hspace{0.17em}/\hspace{0.17em}RT)}\mathrm{liter}/\mathrm{mole·sec}$$ , where $E_0$ is the dissociation energy of N₂F₄, here taken to be 18.4 kcal/mole. For the other gases, the activation energy was unchanged, the relative rate constants being given throughout the temperature range by $k_{\mathrm{He}}{\mathrm{\hspace{0.17em}/\hspace{0.17em}k}}_{\mathrm{Ar}}{\text{\hspace{0.17em}=\hspace{0.17em}1.2\hspace{0.17em}±\hspace{0.17em}0.1, k}}_{\mathrm{SF}6}{\mathrm{\hspace{0.17em}/\hspace{0.17em}k}}_{\mathrm{Ar}}\text{\hspace{0.17em}=\hspace{0.17em}1.7\hspace{0.17em}±\hspace{0.17em}0.2}$ , and $k_{{\mathrm{N}}_2{F}_4}{\mathrm{\hspace{0.17em}/\hspace{0.17em}k}}_{\mathrm{Ar}}\text{\hspace{0.17em}=\hspace{0.17em}1.8\hspace{0.17em}±\hspace{0.17em}0.2}$ . The rate constants are discussed in terms of collision theory.