THETHERMAL DECOMPOSITION OF SOLID ALKALIPERCHLORATES
summary is given in Table 11. (Ti is taken as 2 for each rotational mode (Le., urot = 8 for a three-dimensional rotor).
Table I1 : Numerical Summary of Preexponential Factors at 400°K Y P r e e x p o n e n t i a l factor---Mono-
Case
Bimoleoular
molecular
Bulk Decomposition throughout the Solid, A (sec-1) Case Ia Case I b Case I1 Case I11
1016 10'6 10'6 1012
Not applicable 10'8 1018 10'0
Surface Decomposition, A (sec-1) for 10-p Particles Case I a Case Ib Case I1 Case I11 Case I V
10" 10" 10'2 108
...
... . 1012 1014 106 108
A , (cm/sec) for Regression Rate Case I a Case Ib Case I1 Case I11 Case IV
108 108 109 106
...
2189
... 109 10" 103 108
Conclusions It can be Been from Table I1 that, in contrast to the case of gas-phase reactions, the preexponential factors for solid-phase reactions are expected to have a wide range of values (six or seven orders of magnitude), even after the effect of surface area is corrected for. Empirical first-order preexponential factors may vary from lo5 to 10ls sec-'. The low factors will often indicate a surface reaction, but if the reactions are not dependent on surface area, the low factor may indicate a "tight" complex. The high factors will usually indicate a "loose" complex. Even higher factors (after correction for surface area) can be obtained if the complexes have free translation on the surface. Since in many cases the concentrations in the solid are not controllable, it would have been convenient if the magnitude of the preexponential gave an indication of the molecularity. This appears to be true only for nonsurface-controlled reactions having low (
