The Thermal Decomposition of Hydrogen Peroxide Vapour

The decomposition of hydrogen peroxide vapour at pressures less than 1 mm. in silica vessels has been investigated, mainly at 80 degrees C, but also over the temperature range 15-140 degrees C. Oxygen at low pressures was found to have no appreciable influence on the rate of decomposition; water vapour retarded the rate slightly. The reaction was predominantly a surface one. In one vessel, the decomposition was bimolecular with respect to the peroxide pressure, the rate being given by k[H$\_{2}$O$\_{2}$]$^{2}$/(1 + b[H$_{2}$O])$^{2}$: in another, the bimolecular reaction of the final stages at low peroxide pressures was preceded by one of order approximately 0$\cdot $7 at the high pressures. Higher pressures of oxygen and nitrogen retarded the decomposition appreciably. At higher pressures of water vapour, a pronounced periodicity in rate was evident. The apparent heat of activation over the temperature range investigated was not constant, being calculated as 4200 cal. from rates at 15 and 70 degrees C and 8400 cal. from rates at 80 and 140 degrees C. On the assumption that the lower value more nearly represents the surface reaction, the velocity of decomposition, calculated for 1 mm. pressure of peroxide at 50 degrees C by the theory of absolute reaction rates, was 0$\cdot $70 $\times $ 10$^{13}$ mol.cm.$^{-2}$ sec.$^{-1}$, in agreement with the experimental value of 0$\cdot $76 $\times $ 10$^{13}$ mol.cm.$^{-2}$ sec.$^{-1}$.