Rates of Reaction of Hydrogen with Iodine. II

The rate of reaction of hydrogen with iodine was measured at 666.79° and 799.77°K. The elementary reactions were considered to be $$\begin{array}{cc}& \mathrm{\hspace{0.17em}\rightharpoonup \hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\leftharpoonup }\\ {\mathrm{H}}_2+{\mathrm{I}}_2\text{⇌2}\mathrm{HI}\mathrm{,\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}}& \text{(1)\hspace{0.17em}\hspace{0.17em}(2)}\\ \hspace{0.17em}\mathrm{I}+{\mathrm{H}}_2\rightleftharpoons \mathrm{HI}+\mathrm{H}\mathrm{,\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}}& \text{(3)\hspace{0.17em}\hspace{0.17em}(4)}\\ \hspace{0.17em}\mathrm{H}+{\mathrm{I}}_2\rightleftharpoons \mathrm{HI}+\mathrm{I}\mathrm{,\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}}& \text{(5)\hspace{0.17em}\hspace{0.17em}(6)}\\ \mathrm{\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}}{\mathrm{I}}_2\text{=2}\mathrm{I}\mathrm{,\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}}& \end{array}$$ where the left‐hand equation number applies when the reaction proceeds to the right and the right hand number when the reaction proceeds to the left. Our previous measurements over a shorter and lower temperature range had given E₄∼0 kcal and an apparent temperature dependence for k₄/k₅ which suggested a negative temperature coefficient for k₅. The present more extensive and more precisely treated data show that k₄/k₅ is temperature independent and E₄=0 kcal, E₅=0 kcal. The specific rate [(mole/cc)⁻¹ sec⁻¹] of (3), which at 800°K accounts for about 95% of the HI production, is given by $\log {\mathrm{(k}}_3{\mathrm{/T}}^{\frac{1}{2}}\text{)=12.55±0.07−(32\hspace{0.17em}800±250)/4.575T}$ . The close agreement of our rates with those calculated from data in the literature leads to the conclusion that the experimentally determined values of k₄/k₅ are equal to values of k₄/k₅ for thermal energy distributions of H atoms.