Further development of the reaction mechanism

3 FURTHER DEVELOPMENT OF THE REACTION MECHANISM 4.3.1 Slow reaction 

since competition between reactions (xi) and (v) or (vb) is excluded by the second limit behaviour referred to in Sect. 4.2 immediately above, the peroxide must be formed by mutual interaction of two HO2 radicals either at the surface by reaction (va) or in the gas phase by reaction (x) below. Second, the autocatalytic nature of the reaction can only be attributed to the dissociation of H2 Oj by reaction (vii) or the alternative (viia). Competition between the dissociation and a surface destruction of H2O2 would introduce a diameter dependence of the rate which is contrary to the results. A second function of the ageing of the surface therefore must be to eliminate surface destruction of the peroxide. Third, if H2O2 always dissociates by (vii) or (viia), the formation of HO2 by reaction (iv) always leads to a chain propagating cycle 

Superimposed on this will be chain branching due to reactions (ii) and (iii), and unless some form of chain termination is introduced the reaction will always be explosive. The termination must be gas phase in order to account for the absence of a diameter effect, and since the observed overall activation energy of 57 kcal. mole is close to the expected activation energy of reaction (vii), the terminating reactions probably compete with (vii) for H2O2. Possible reactions are (vi), (xiii), (xiv) and 

The boric acid type of second limit behaviour was shown by Egerton and Warren [24] to be obtained by introducing a quadratic branching step 

However, under quadratic branching conditions the steady state concentration of chain centres is given by 

---