Autocatalysis intensity

This equation includes the particular cases of an nth order reaction model with g(a) = 1, and the autocatalytic model with g(a) = 1 + la, where / is the autocatalysis intensity. In general, the form of g(a) must be determined from experimental data. 

The kinetics of the reactions were complicated, but three broad categories were distinguished in some cases the rate of reaction followed an exponential course corresponding to a first-order form in others the rate of reaction seemed to be constant until it terminated abruptly when the aromatic had been consumed yet others were susceptible to autocatalysis of varying intensities. It was realised that the second category of reactions, which apparently accorded to a zeroth-order rate, arose from the superimposition of the two limiting kinetic forms, for all degrees of transition between these forms could be observed. 

Reducing the temperature or increasing the concentration of reactants, particularly of dinitrogen pentoxide, advanced the onset and increased the intensity of the autocatalysis. Added nitric acid and, to a greater extent sulphuric acid, made the effect more prominent. 

Three model kinetic schemes have been studied relatively intensively with periodic forcing the first-order non-isothermal CSTR of chapter 7 the Brusselator model, which is closely related to the cubic autocatalysis of chapters 2 and 3 and the surface reaction model discussed in 12.6. We will use the last of these to introduce some of the general features. 

Aqueous solutions of the compounds were prepared and exposed In duplicate In 1 cm 10 cm Fyrex test tubes at concentrations comparable with those In aqueous CRM-1. After exposure, the samples were extracted and analyzed by GC using an Internal standard. Figure 2 shows the first-order plots for the photolysis of these compounds for exposure periods of either 60 min or 180 min, depending on the Individual rates. Autocatalysis Is apparent In the case of 2-MI, 3-MI, and 5-MI. For 2-MI and 3-MI, the catalyzed rates appear to be first order. Photolysis of indole and 7-MI proceeded at slower rates whether autocatalysis occurred cannot be ascertained from the data. The results for carbazole show no Indication of autocatalysis. The photolysis rate observed Is linear up to two half-lives, after which It begins to level off, possibly due to diminishing sunlight Intensity. 

Situations of this type are grouped under the term autocatalysis, which means that the system produces its catalyst as it goes along. As in the growth of populations, the acceleration can become so intense that the word explosion properly describes the catastrophic event. The explosion may fizzle if reactants are exhausted before the situation has gone out of hand — the rate... 

Oscillating chemiluminescence has been observed in the H2O2/KSCN/ CuS04/NaOH/luminol system there are two types of oscillation, and the low-intensity mode may involve the reaction of superoxide with luminol. A simplified mechanism for the methylene-blue/HS /02 oscillation in a CSTR has been proposed. Experimental and modeling structures of oscillation in the C102/l2/malonic acid system show that the oscillations are not due to autocatalysis but to self-inhibition in the ClOf/I reaction. A study of the oxidation of hexacyanoferrate(II) by bromine is concluded to involve the formation of Brf as an intermediate, formed in the first step. The aerobic oxidation of NADH catalyzed by horse radish peroxidase... 

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