Rates of Reaction of Hydrogen with Iodine. II

Abstract

The rate of reaction of hydrogen with iodine was measured at 666.79° and 799.77°K. The elementary reactions were considered to be ⇀ ↼H2+I2⇌2HI, (1) (2) I+H2⇌HI+H, (3) (4) H+I2⇌HI+I, (5) (6) I2=2I, 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(k3/T12)=12.55±0.07−(32 800±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.