Oxidation-Reduction Theory

A major class of chemical reactions involves the transfer of one or more electrons from one species to another. This process is referred to as an electron-transfer or oxidation-reduction reaction, where the species nndergoing electron loss is said to be oxidized, while the species acquiring electrons is reduced. Pyrotechnics, propellants, and explosives belong to this chemical reaction category. 

The determination of whether or not a species has undergone a loss or gain of electrons during a chemical reaction can be made by assigning oxidation numbers to the atoms of the various reacting species and products, according to the following simple rules  

Except in a few rare cases, hydrogen is always +1 and oxygen is always -2. Metal hydrides and peroxides are the most common exceptions. This rule is applied first—it has highest priority, and the rest are applied in decreasing priority. 

Simple ions have their charge as their oxidation number. For example, 

The oxidation nnmber of an elanent in its standard state (either as a monatomic atom snch as metallic iron, Fe, or combined with itself to form a diatomic molecule, as in Nj or Oj) is 0. 

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ELECTRON TRANSFER REACTIONS Oxidation-Reduction Theory... 

The color and constitution of cyanine dyes may be understood through detailed consideration of their component parts, ie, chromophoric systems, terminal groups, and solvent sensitivity of the dyes. Resonance theories have been developed to accommodate significant trends very successfully. For an experienced dye chemist, these are useful in the design of dyes with a specified color, band shape, or solvent sensitivity. More recendy, quantitative values for reversible oxidation—reduction potentials have allowed more complete correlation of these dye properties with organic substituent constants. 

In theory, any oxidation-reduction reaction can be set up in a cell to do electrical work. The amount of reversible1 work is easily calculated. If, during the discharge of a cell, a quantity of electricity Q flows through the external circuit at a constant potential, the amount of electrical work, n e, produced is given by... 

Study, the students are taught the basic concepts of chemistry such as the kinetic theory of matter, atomic stmcture, chemical bonding, stoichiometry and chemical calculations, kinetics, energetics, oxidation-reduction, electrochemistry, as well as introductory inorgarric and organic chemistry. They also acquire basic laboratory skills as they carry out simple experiments on rates of reaction and heat of reaction, as well as volrrmetric analysis and qualitative analysis in their laboratory sessions. 

When developed, this theory proved to be more general than the theory of Lewis, for it includes all the above acid-base definitions and also includes oxidation-reduction reactions. 

Marcus RA. 1956. On the theory of oxidation-reduction reactions involving electron transfer. I. J Chem Phys 24 966-979. 

Chemical detoxification uses oxidation, reduction, neutralization, and hydrolysis to reduce the toxicity of the contaminants. The basic theory is similar to that of treating pumped groundwater. 

The discussion and classification of reagents is masterful in identifying Ingold s new nomenclature and principles with more widely known oxidation-reduction and acid-base theory. The 1953 lectures at Cornell University, published as Structure and Mechanism in Organic Chemistry, follow this same strategy, showing how old classification schemes overlap with each other and how apparent inconsistencies disappear as old schemes are incorporated into the new one. Nineteenth-century Berzelian electrochemical dualism, revived by Lapworth and Robinson in the cationic/anionic schema, disappears into the electrophilic/nucleophilic language. 

It is well known that the flotation of sulphides is an electrochemical process, and the adsorption of collectors on the surface of mineral results from the electrons transfer between the mineral surface and the oxidation-reduction composition in the pulp. According to the electrochemical principles and the semiconductor energy band theories, we know that this kind of electron transfer process is decided by electronic structure of the mineral surface and oxidation-reduction activity of the reagent. In this chapter, the flotation mechanism and electron transferring mechanism between a mineral and a reagent will be discussed in the light of the quantum chemistry calculation and the density fimction theory (DFT) as tools. 

This chapter mainly focuses on the reactivity of 02 and its partially reduced forms. Over the past 5 years, oxygen isotope fractionation has been applied to a number of mechanistic problems. The experimental and computational methods developed to examine the relevant oxidation/reduction reactions are initially discussed. The use of oxygen equilibrium isotope effects as structural probes of transition metal 02 adducts will then be presented followed by a discussion of density function theory (DFT) calculations, which have been vital to their interpretation. Following this, studies of kinetic isotope effects upon defined outer-sphere and inner-sphere reactions will be described in the context of an electron transfer theory framework. The final sections will concentrate on implications for the reaction mechanisms of metalloenzymes that react with 02, 02 -, and H202 in order to illustrate the generality of the competitive isotope fractionation method. 

A very useful extension of the voltammetric technique is cyclic voltammetry (Adams, 1969 Cauquis and Parker, 1973) in which one scans the potential of the working electrode in an unstirred electrolyte solution in the anodic (cathodic) direction and records one or several peaks due to oxidation (reduction) of the substrate. At some suitable potential, the direction of the scan is reversed and peaks due to reduction (oxidation) of intermediates and/or products formed during the forward scan are observed. In the simplest case a linear increase (decrease) of the potential with time is employed (triangular cyclic voltammetry) with scan rates in the range 0 01-1000 V s 1. It should be noted that cyclic voltammetry at scan rates above 1 Vs"1 requires the use of a differential cell to reduce the residual current due to charging of the electrified interface (see, for example, Peover and White, 1967). The theory of cyclic voltammetry has been... 

The confusion in theories is considerable, and is not much enlightened by the great variety of mathematical treatment, much of which, as seems all too frequent nowadays, appears to contain conveniently adjustable constants. It is to be hoped, however, that clear discussion on the lines of Gurney s treatment of the reversible electrode mentioned in 4, is not far distant. At present, it certainly seems as if the rate of recombination of adsorbed hydrogen atoms is important, perhaps of predominating importance. If the transfer of electrons from metals to ions in solution were intrinsically a slow process, the oxidation-reduction electrodes would not be reversible. 

Silver halide microcrystals are wide band gap semiconductors which exhibit weak photoconductivity. Early experiments demonstrated that dyes that sensitized silver halide photographic action also sensitized silver halide photoconductivity [6c]. Since the observation of photoconductivity necessitates the movement of free charge within the crystals, dye sensitization processes must inject charge into the silver halide lattice in some way. Initial theories of sensitization were based on the semiconductor view of silver halides, especially as espoused by Gurney and Mott [10]. Current ideas are based on thorough studies of the absorption spectroscopy and luminescence of silver halide emulsions and of adsorbed, sensitizing dyes, and the oxidation-reduction properties of the dyes at silver/silver halide electrodes [11]. 

Net ionic equations are used in discussions of limiting quantities problems (Chapter 10), molarities of ions (Chapter 11), balancing oxidation-reduction equations (Chapter 16), acid-base theory (Chapter 19), and many other areas beyond the scope of this book. They make possible writing equations for halfreactions at the electrodes in electrochemical experiments (Chapter 17), which have electrons included explicitly in them. They make understandable the heat effects of many reactions such as those of strong acids with strong bases. 

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