Arrhenius plots general form, 22

The pressure dependence of methyl recombination is another factor which must be taken into account when relation (35) is applied. The values corrected by Dodd for this pressure dependence can be seen in Figure 10. The Arrhenius plot is reasonable, and the agreement of the data obtained from different sources is generally good, though some methane was probably formed at low temperatures by a wall reaction of CH3 in the photolysis at 3130 The best straight line drawn... 

In the discussion so far, orders of one or two have been considered. Surface processes with other orders (and fractional orders) have been found and changes in Arrhenius plot slopes can be caused by changes in desorption mechanism. Equation (94) shows the general form of the dependence of the kinetic parameters on the desorption order in terms of initial coverages. Another important relationship can be derived from the work of Falconer [280] who showed that... 

The values of Nch4 determined in the present work are plotted in Arrhenius form in Figure 3 the activation energy determined from the slope of this line is 24.6 kcal/mol. For comparison, the values of Nch4 measured for both polycrystalline nickel foil and high-area-supported nickel catalysts are also shown. The rates are all normalized to a 4 1 H2 C0 mixture at a total pressure of 120 Torr. Generally speaking, a... 

However, real solids are more complex. In the common case where the concentration of the diffusant is much higher than that of vacant sites, one must consider vacancies as the diffusing entities, in a similar fashion to the hole formalism used in semiconductors. More generally, the concentration to be used is that of the diffusing lattice defects, e.g. vacancies, interstitial ions, etc. The result is still of the Arrhenius form, however, and plots of In(crr) vs. l/T are linear with a slope of — EJkT. Consequently, the requirement for high mobility is simply a low activation energy, as expected for an open structure. 

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