Kinetics of Thermal Decomposition of Aqueous Perchloric Acid

Abstract

Thermal decomposition of 1.1–6.6 m aqueous perchloric acid at 295–322° yields oxygen, chlorine, and a small quantity of hydrochloric acid. The initial rates of decomposition have been measured, using a perchlorate ion activity electrode, and show 3.5 order dependence on the stoichiometric perchloric acid concentration; the corresponding rate coefficient and activation energy at 300.0° are 3.1 × 10-7 m −2.5 s−1 and 84 kcal mole−1, respectively. The order of reaction with respect to time is less than 3.5 and depends upon the initial perchloric acid concentration; this effect is due to acceleration of the decomposition by the reaction products, notably chloride ion. It is suggested that the rate-determining step in the decomposition of aqueous perchloric acid is the reaction of two undissociated HClO4 molecules to give H2O, ClO3, and ClO4.