Kinetics of fast reactions

Describe in brief the techniques which can be used to study the kinetics of fast reactions. 

Houcine et al. (64) used a non-intrusive laser-induced fluorescence method to study the mechanisms of mixing in a 20 dm CSTR with removable baffles, a conical bottom, a mechanical stirrer, and two incoming liquid jet streams. Under certain conditions, they observed an interaction between the flow induced by the stirrer and the incoming jets, which led to oscillations of the jet stream with a period of several seconds and corresponding switching of the recirculation flow between several metastable macroscopic patterns. These jet feedstream oscillations or intermittencies could strongly influence the kinetics of fast reactions, such as precipitation. The authors used dimensional analysis to demonstrate that the intermittence phenomenon would be less problematic in larger CSTRs. 

Jhe discovery by radiation chemists of solvated electrons in a variety of solvents (5, 16, 20, 22, 23) has renewed interest in stable solutions of solvated electrons produced by dissolving active metals in ammonia, amines, ethers, etc. The use of pulsed radiolysis has permitted workers to study the kinetics of fast reactions of solvated electrons with rate constants up to the diffusion-controlled limit (21). The study of slow reactions frequently is made difficult because the necessarily low concentrations of electrons magnify the problems caused by impurities, while higher concentrations frequently introduce complicating second-order processes (9). The upper time limit in such studies is set by the reaction with the solvent itself. 

Another chemical relaxation method that can be used to determine the kinetics of fast reactions on soil constituents is the electric field pulse technique. This technique was developed by Hachiya et al. (1980) to study the kinetics of I03 adsorption and desorption on Ti02 and by Sasaki et al. (1983) to investigate ion-pair formation on the surface of a-FeOOH. Excellent review articles on electric field methods are found in DeMaeyer (1969), Hemmes (1979), and Eyring and Hemmes (1986). 

The relatively long equilibration time of the stagnant thin layer of the OTTLE or reflection cell does not allow one to study the kinetics of fast reactions. Alternatively, the forced convection regimes of the RDE and the channel-flow cell allow production of steady state currents, and both have been investigated with optical detection of electrogenerated species. Further details can be found in Chapter 2.4 in this volume. The rotating OTE was investigated early on and the theory has recently been expanded [204]. The electrode is used... 

Bewick, A., Fleischmann, M. and Huddleston, J.N. (1966) The determination of the kinetics of fast reactions in solution by electrochemical methods. Proceedings of the 3rd International Conference on Polarography, Southampton, p. 57. 

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