Energy sources redox reactions

In principle at least, any spontaneous redox reaction can serve as a source of energy in a voltaic cell. The cell must be designed in such a way that oxidation occurs at one electrode (anode) with reduction at the other electrode (cathode). The electrons produced at the anode must be transferred to the cathode, where they are consumed. To do this, the electrons move through an external circuit, where they do electrical work. 

Another spontaneous redox reaction that can serve as a source of electrical energy is that between zinc metal and Co3+ ions ... 

Electrolytic cell A cell in which the flow of electrical energy from an external source causes a redox reaction to occur, 481, 509q cell reactions, 498 diagram of, 486... 

Flavins — Riboflavin is first of all essential as a vitamin for humans and animals. FAD and FMN are coenzymes for more than 150 enzymes. Most of them catalyze redox processes involving transfers of one or two electrons. In addition to these well known and documented functions, FAD is a co-factor of photolyases, enzymes that repair UV-induced lesions of DNA, acting as photoreactivating enzymes that use the blue light as an energy source to initiate the reaction. The active form of FAD in photolyases is their two-electron reduced form, and it is essential for binding to DNA and for catalysis. Photolyases contain a second co-factor, either 8-hydroxy-7,8-didemethyl-5-deazariboflavin or methenyltetrahydrofolate. ... 

Also ascomycetes yeast strains showed decolorizing behaviors due to extracellular reactions on polar dyes. The process occur when an alternative carbon and energy source is available. The involvement of an externally directed plasma membrane redox system was suggested in S. cerevisiae, the plasma membrane ferric reductase system participates in the extracellular reduction of azo dyes [25]. 

Combustion reactions are redox reactions in which the chemical species rapidly combines with oxygen and usually emits heat and light. Reactions of this type are extremely important in our society as the sources of heat energy. Complete combustion of carbon yields carbon dioxide, and complete combustion of hydrogen yields water. The complete combustion of hydrocarbons, organic compounds containing only carbon and hydrogen, yields carbon dioxide and water ... 

For electrochemists whose principal objective is analysis of constituents in solution, the path is straighter and the hill less steep. The reaction model often used is a redox reaction in which the interfacial reaction is simply electron transfer, and surface chemical reactions among radicals can be neglected. The electrode is regarded as stable during the reaction and is not intended to take any chemical part in it. The function of the surface is not electrocatalytic, it is simply to be a source and sink of electrons, the energy of which may be controlled by variation of the electrode potential. 

The example illustrates that enthalpy can be gained when nonpolar bonds, as commonly encountered in organic molecules, are broken and polar bonds, such as those in carbon dioxide and water, are formed. Reactions which involve the transfer of electrons between different chemical species are generally referred to as redox reactions. Such reactions form the basis for the energy production of all organisms. From this point of view we can consider organic compounds as energy sources. 

Ene way to meet the energy needs of the future is to find effective ways of generating electricity from chemical reactions. Small but efficient sources of electricity are needed for portable equipment, from artificial hearts and pocket computers to electric automobiles and space habitats. We shall see in this chapter how chemical reactions—particularly redox reactions—can provide this energy. 

It should be noted that the main amount of redox enzymes in animal and plant cells is accumulated in mitochondria, which are usually called the power plants of the cell, because redox reactions supplying cells with energy proceed in them. Therefore, at present, mitochondria are the main source of information about biological oxidation and energetic conjugation mechanisms. 

The chemical species shown on the left are oxidants (oxidizing agents) which can be regarded as possessing vacant electron-free energy levels. A redox reaction will be spontaneous only if the reductant ( electron source in the table) is located above that of the desired electron sink . 

During the PEVD process, a chemical redox reaction takes place and the whole PEVD system can he viewed as a chemical reactor where the reactants are distributed over both the source and sink sides. According to the previous discussion, the driving force for this PEVD process can be solely provided by a dc electric potential, so that isolation of the source and sink vapor phases is not necessary. Consequently, the PEVD process is equivalent to physically moving a solid phase Na COj through another solid phase (Na+-[3"-alumina) by electric energy. Furthermore, it should be pointed out that the overall cell reaction in this PEVD system is reversible. 

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