Opposing Reactions Higher Orders

Two further cases of opposing reactions which can be easily resolved by present methods may be mentioned. They are opposing reactions of second order and of mixed order. 

Case 1. The example of opposing reactions of second order may be represented by the equations 

For simplicity we shall also assume that this represents the stoichiometry. The rate equation is 

Once again the equation is difficult to use experimentally unless h and are known, or at least unless their ratio is known. This knowledge may be obtained from a study of the equilibrium concentrations. Once known the data can be plotted and the individual specific rate constants determined. 

Case 2. A case of mixed first- and second-order reaction can be represented by 

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An excellent review of higher order reactions, opposing reactions, consecutive reactions, etc, is given in Chapts II III of Ref. 10 and in Ref 11... 

For a system of two opposing first-order reactions one would expect first-order behavior, as experimentally observed. In relaxation kinetics, however, even non-first-order reactions will exhibit first-order kinetics provided the perturbation of the system is small enough so that higher-order terms in x can be neglected. For a system of opposing second- and first-order reactions, Eq. 21,... 

It has been shown that the sol-gel materials can be used as host matrices for a variety of biological molecules (7-77). The dopant biomolecules reside in the porous network of these sol-gel composite materials as a part of nanostructured architecture. The unique nanostructured assembly of such sol-gel composites is characterized by biomolecules enclosed in the nanopores of the material. The bioparticles arranged as part of sol-gel composites are characterized by intermediate order and mobility, as opposed to the higher degrees of order available in solids or the pronounced mobilities present in solution media. In other words, the properties of both the solid and solution phases prevail in sol-gel environment. In spite of general similarity in reaction chemistry with macroscopic solution based discipline, variation in overall reaction kinetics can be observed as a direct consequence of encapsulation. Usually it is the interactions of the dopant molecules with the sol-gel matrix that determine the reaction pathways a particular system undergoes. Such a nanostructured system utilizes the properties of spatially isolated molecules in a solvent-rich environment necessary for stability of the biomolecules. 

One of the main aspects of modem chemistry is the safety of the chemical processes. It is easy to see that the volume of a batch reactor must be some orders of magnitude higher than that of the continuous-flow microreactor to reach the identical quantity of final products (using equal amounts of reactants). The small quantity of reactants in the reactor minimizes the potential of thermal explosion by dangerous reactions. Indeed, explosion or depressurization of reaction systems with hazardous substances in the continuous microreactors leads only to insignificant technical problems or to a minimum leakage of chemicals, as opposed to the scales of explosions or leaks in standard reactor volumes. Microreactors, with their narrow channel dimensions, hold such a small quantity of reaction fluid that a mechanical failure in one reactor requires merely a temporary shutdown and subsequent replacement. 

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