Chemical reaction highly reversible systems

The high temperatures generated by concentrated solar power can be used to drive chemical reactions. The reverse reaction releases the chemically stored energy as thermal energy. Various systems have been investigated, such as the dissociation of sulphur trioxide (De Maria et al., 1985) ... 

Water generally is used for gases fairly soluble in water, oils for light hydrocarbons, and special chemical solvents for acid gases such as CO9, SO9, and H9S. Sometimes a reversible chemical reaction will result in a veiy high solubility and a minimum solvent rate. Data on actual systems are desirable when chemical reactions are involved, and those available are referenced later under Absorption with Chemical Reaction. ... 

In this case a vapour-liquid system, where high concentrations occur and ail components are volatile, will be considered. The liquid and vapour bulk are not in physical equilibrium. In the liquid phase the following reversible chemical reaction occurs ... 

The influence of the chemical follow-up reaction depends on the ratio of the rate constant kc of the C step and the sweep rate v. The higher that v is, the less influence does the follow-up reaction have for chemical reactions with first-order rate constants kc 104, it is possible to outrun the reaction and obtain a reversible cyclic voltammogram at high v. The p(red) for a given system with first-order (or pseudo first-order) kinetics is then shifted 30 mV in the negative direction when v is increased tenfold.11-15 By plotting Ep versus log v, one can get curves from which the value of kc can be obtained. This is illustrated in Fig. 3 for a reaction where the chemical step is a cleavage. 

The fact that US influences the mechanism of chemical reactions via the action of highly reactive radicals such as OH- and H- formed during solvent sonolysis is well known (see Chapter 7). Solvents sensitive to thermolysis or sonolysis (e.g. dimethylformamide [158], dimethylsulphoxide [159]) decompose slowly in the presence of intense US. Thus, radical species formed by cavitation are highly reactive and may participate as activators or enhancers in the electrode process [160]. In fast, qt/asr-reversible or irreversible systems, however, the only effect of US is to enhance mass transport without any direct effect on the rate of simple electron transfer processes. 

In addition to the freeze-concentration effect, a catalytic role for ice crystals, a favorable orientation of substrate and biocatalyst, the markedly lower dielectric constant of ice compared with water, and the high proton mobility in ice, have been discussed as further factors that possibly influence reactions in frozen systems. In summary, the reverse action of hydrolases provides an attractive alternative to the chemical synthesis of peptides but this approach could also be verified for the synthesis of oligosaccharides and oligonucleotides using glycosidases and ribonu-cleases, respectively11631. 

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