Rates of Reaction of Hydrogen with Iodine

The rates of reaction of hydrogen with iodine have been measured at 633.21°, 666.79°, 710.33°, and 737.93°K with at least a tenfold variation in the hydrogen and iodine concentrations at each temperature. The data have been treated considering the elementary reactions to be $$\begin{array}{c}{\mathrm{I}}_2\text{⇌2}\mathrm{I}\\ \text{(1)}{\mathrm{H}}_2+{\mathrm{I}}_2\text{→2}\mathrm{HI}\\ \text{(2)}\mathrm{HI}\to {\mathrm{H}}_2+{\mathrm{I}}_2\\ \text{(3)}\mathrm{I}+{\mathrm{H}}_2\to \mathrm{HI}+\mathrm{H}\\ \text{(4)}\mathrm{H}+\mathrm{HI}\to {\mathrm{H}}_2+\mathrm{I}\\ \text{(5)}\mathrm{H}+{\mathrm{I}}_2\to {\mathrm{H}}_2+\mathrm{I}\\ \text{(6)}\mathrm{I}+\mathrm{HI}\to {\mathrm{I}}_2+\mathrm{H}.\end{array}$$ This classical reaction has long been considered to consist solely of the simple bimolecular reactions (1) and (2). However, the atom mechanism, reactions (3) to (6), is shown to account for 10% of the over‐all reaction at 633° and 27% at 738°K when the iodine pressure is one‐half atmosphere. The three independent constants k₁, k₃, and k₄/k₅ in (mole/cc)^—1 sec^—1, are given by log₁₀(k₁/T^½) = 12.78–40740/4.575T, log₁₀(k₃/T^½) = 12.75–33440/4.575T, and k₄/k₅ = 0.07, 0.082, 0.117, 0.125 at the experimental temperatures 633°, 667°, 710°, and 738°K.