Simultaneous interdependent reactions

In complex reacting systems, such as those in combustion processes, a simple one-step rate expression will not suffice. Generally, one finds simultaneous, interdependent reactions or chain reactions. 

The most frequently occurring simultaneous, interdependent reaction mechanism is the case in which the product, as its concentration is increased, begins to dissociate into the reactants. The classical example is the hydrogen-iodine reaction  

The rate of formation of HI is then affected by two rate constants, kr and kb, and is written as 

With this equilibrium consideration the rate expression for the formation of HI becomes 

In most instances, two reacting molecules do not react directly as H2 and I2 do rather one molecule dissociates first to form radicals. These radicals then initiate a chain of steps. Interestingly, this procedure occurs in the reaction of H2 with another halogen, Br2. Experimentally, Bodenstein [12] found that the rate of formation of HBr obeys the expression 

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An agitated liquid-liquid process involves many simultaneous, interdependent phenomena, such as dispersion, coalescence, suspension, heat and mass transfer, and chemical reaction. Previously described nitration requires control of the interfacial area rather than specific drop size, but some processes require precise control of drop size. For example, equipment for suspension polymerization processes must be capable of producing uniform beads of specified size range as well as providing for heat transfer and drop suspension. 

To gain understanding of the interdependence between the olefin reduction and the sulfoxide reduction, the saturated sulfoxide 52 was prepared and treated with BH3-THF. No reaction was observed under the similar conditions (Scheme 5.18). The unactivated vinyl sulfide 16 was also not reactive toward BH3-THF. These results indicated that sulfoxide and olefin were reduced simultaneously, not independently. Again this phenomenon was unexpected and pointed to the unique nature of this reaction. 

A major drawback of molar mass control by changing ftAl/ Nd rati°s is the simultaneous alteration of polymerization rates. As shown for the system NdV/DIBAH/EASC, an increase in nDiBAH/ Ndvrati°s from 10 to 30 reduces molar mass by 73% but also doubles the rate of polymerization [178,179]. For NdV/TIBA/EASC the variation of ftTiBA/ Ndv from 10 to 30 reduces molar masses by 78% but increases the polymerization rate even 27-fold (Fig. 11) [179]. As shown by these two examples, on one hand, variations of ftAi/ Nd-ratios have a considerable effect on molar mass, and on the other hand, lead to an undesired side effect regarding reaction rates. Because of these interdependencies, in the large-scale continuous production of Nd-BR, adjustments of the ftAl/ Ndv rati°s have to be counteracted by adaptations of residence time in order to keep monomer conversion per reactor and fi-... 

A particular contribution of thermodynamics of non equilibrium pro cesses is the possibihty of describing an interference of various processes that proceed simultaneously in non equihbrium systems. A spectacular example of the interference is interdependence of the rates of various stoichiometric stepwise chemical processes (i.e. transformations with a set of intermediate steps) with the common reaction intermediates. 

The ultimate test of catalyst performance is the vehicle test described in Section 1.2. In such a vehicle test all the reaction conditions that influence the conversion reached over the catalyst vary simultaneously in a interdependent fashion, as they are fixed by the speed and the load of the vehicle at each moment of the test. For research and development purposes, however, it is useful to evaluate the catalyst performance using fewer parameters or parameters that can be varied independently. Several simplified test procedures have therefore been developed. 

It should be noted that GC mode experiments with amperometric tips may contain a feedback component to the current if the electrochemical process at the tip is reversible and the tip-to-specimen distance is less than about 5a. However, at greater distances or when employing a potentiometric tip, the tip acts approximately as a passive sensor, i.e., one that does not perturb the local concentration. This situation is quite distinct from feedback mode, where the product of the electrolysis at the tip is an essential reactant in the process at the specimen surface. This interdependence of tip and specimen reactions in feedback mode ensures that the biochemical process is confined to an area under the tip defined by the tip radius and diffusional spreading of the various reagents (20). In contrast, the biochemical process in GC mode is independent of the presence of the tip and may therefore occur simultaneously across the whole surface. In addition, the tip signal often does not directly provide information on the height of the tip above the surface methods to overcome this limitation are described in Sec. I.D. Finally, since the tip process and the biochemical reaction at the specimen are independent, a wide range of microsensors may be employed as the tip, e.g., ion-selective microelectrodes, which are not applicable in feedback experiments. 

Ion hydrolysis and solid dissolution reactions occur at the same time in the soil solution and many of these reactions are interdependent. One hydrolysis reaction that releases H+, for example, affects the other hydrolysis reactions and solids containing OH- ligands. The advent of computers allowed rapid calculation of many simultaneous reactions, and this was soon applied to models that try to calculate the composition of the soil solution and natural waters. 

C3H5 A. (OH)2 + H. OH = A. H + C3H6(OH)3 (Glycerol). These reactions are interdependent. The rate of formation of glycerol is conditioned by the rate of formation of monoacetin the rate of monoacetin depends, in turn, upon the rate of formation of diacetin. There are, thei efore, three simultaneous reactions of the second order taking place in the system. 

If condition (3.22) is foimd to be satisfied over the whole process, then the -th species may be excluded from the reaction scheme. Naturally, such a procedure helps to identify the redundant steps in the reaction kinetic scheme. One more important factor is related to the criterion (3.22), demonstrating the concentration interdependence between the reaction species, and consequently, between the different steps of a complex reaction. Such an interdependence is not immediately present in the parameters, which determine the step sensitivity. For this reason the simultaneous use of the step sensitivity criteria and the reaction species makes the process of reducing the reaction mechanisms more effective. 

The intrinsic pathway generates active enzymes by a multitude of interdependent chemical reactions. Simultaneously platelets adhere to the protein-coated implant and form pyramid shaped aggregates which release phospholipid molecules and these accelerate the intrinsic clotting process. 

The preceding chapter deals with the multiplicity of reactions that proceed simultaneously and with considerable interdependence. Now we come to the question of how metabolism is regulated and adapted to the requirements of an organism. 

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