Oxidation-reduction reactions in solution

Spiro [27] has derived quantitative expressions for the catalytic effect of electron conducting catalysts on oxidation-reduction reactions in solution in which the catalyst assumes the Emp imposed on it by the interacting redox couples. When both partial reaction polarization curves in the region of Emp exhibit Tafel type kinetics, he determined that the catalytic rate of reaction will be proportional to the concentrations of the two reactants raised to fractional powers in many simple cases, the power is one. On the other hand, if the polarization curve of one of the reactants shows diffusion-controlled kinetics, the catalytic rate of reaction will be proportional to the concentration of that reactant alone. Electroless metal deposition systems, at least those that appear to obey the MPT model, may be considered to be a special case of the general class of heterogeneously catalyzed reactions treated by Spiro. 

Three classes of polynuclear complexes containing metal-metal bonds possess emissive excited states that undergo oxidation-reduction reactions in solution the prototypes are Re2Cl T(dlt d lt),... 

In view of the great importance of chemical reactions in solution, it is not surprising that basic aspects (structure, energetics, and dynamics) of elementary solvation processes continue to motivate both experimental and theoretical investigations. Thus, there is growing interest in the dynamical participation of the solvent in the events following a sudden redistribution of the charges of a solute molecule. These phenomena control photoionization in both pure liquids and solutions, the solvation of electrons in polar liquids, the time-dependent fluorescence Stokes shift, and the contribution of the solvent polarization fluctuations to the rates of electron transfer in oxidation-reduction reactions in solution. 

As a second example of how one interprets kinetic data in terms of mechanism, some simple electron-transfer (oxidation-reduction) reactions in solution are discussed. A complete review of this subject is not intended instead, we consider mainly the reduction of Co(NH3)5X by Cr " (aq) and Cr(bipy)3. Here X " can be any of a number of ligands, such as H2O, Cr, Br, OH , etc., and bipy is a,a -bipyridine. At a constant pH, the rate law for the oxidation-reduction reaction is first order in each of the reactants. The second-order rate constant is often dependent on pH because the reactants can exist in different ionized forms which react at different rates. We... 

Among oxidation-reduction reactions in solution, the formally simplest type is that in which an electron is transferred between two ions of variable valency, without change in the number or the nature of the ligands attached to the ions. These reactions have been intensively studied, mainly in aqueous solution. Some examples of such electron-transfer reactions are ... 

In addition to simple dissolution, ionic dissociation and solvolysis, two further classes of reaction are of pre-eminent importance in aqueous solution chemistry, namely acid-base reactions (p. 48) and oxidation-reduction reactions. In water, the oxygen atom is in its lowest oxidation state (—2). Standard reduction potentials (p. 435) of oxygen in acid and alkaline solution are listed in Table 14.10- and shown diagramatically in the scheme opposite. It is important to remember that if or OH appear in the electrode half-reaction, then the electrode potential will change markedly with the pH. Thus for the first reaction in Table 14.10 O2 -I-4H+ -I- 4e 2H2O, although E° = 1.229 V,... 

In solution, NaOCl dissociates into sodium ions (Na+) and hypochlorite ions (OC1). Bleaching involves an oxidation-reduction reaction in which the Cl in the OC1 ion (oxidizing agent) is reduced to the chloride ion (Cl ). The reducing agent is either a dye, which fades, or the stain being removed. 

The electrochemical treatment of contaminated groundwater technology uses direct electrical current applied between two immersed electrodes to produce oxidation-reduction reactions in aqueous solutions. Positively charged metal ions are attracted to the negatively charged electrode (the cathode), where they are reduced. 

C, Photo-oxidation-reduction or Redox-reactions. A photo-oxidation-reduction process in solution may be intramolecular when the redox reaction occurs between the central metal atom and one of its ligands or intermolecular when the complex reacts with another species present in the solution. 

For oxidation-reduction reactions in aqueous solution under an externally applied electrical potential, or in its absence, one can write O for the oxidized species and R for the reduced species, and the half-cell reaction can be written as... 

Some chemists prefer to use the ion-electron method for oxidation-reduction reactions carried out in dilute aqueous solutions, where free ions have a more or less independent existence, and to use the oxidation-state method for oxidation-reduction reactions in other liquid media, in solids, or in gases. 

Hyponitrites undergo various oxidation-reduction reactions in acid and alkaline solutions, depending on conditions they usually behave as reducing agents, however. 

The group RuNO can occur in both anionic and cationic octahedral complexes in which it is remarkably stable, being able to persist through a variety of substitution and oxidation-reduction reactions. Ruthenium solutions or compounds that have at any time been treated with nitric acid can be suspected of containing nitric oxide bound to the metal. The presence of NO may be detected by infrared absorption ca. 1930-1845 cm-1. 

Balancing Oxidation-Reduction Reactions In Aqueous Solution... 

Reduction Equations The Half-Reaction Method for Balancing Oxidation-Reduction Reactions in Aqueous Solutions... 

Oxidation-reduction reactions in aqueous solutions are often complicated, which means that it can be difficult to balance their equations by simple inspection. In this section we will discuss a special technique for balancing the equations of redox reactions that occur in aqueous solutions. It is called the half-reaction method. 

In the following paragraphs, oxidation/reduction reactions in sediments and authigenic mineral formation are discussed. The effects of these reactions on the sedimentary environment are illustrated using profiles of solutes in sedimentary pore waters at a near-shore location. Then, there is a brief discussion of the role that sedimentary chemical processes play in nutrient cycles and the cycling of anthropogenic contaminants. 

In this chapter we will consider some additional fundamental aspects of chemical reactions, i.e., how they occur, the driving forces behind them, and their dependence upon specifics of molecular structure and conditions of reaction, such as temperature and concentration. There are two aspects of chemical reactions which, though interrelated, are dealt with as separate topics. The first of these is the study of the reaction from its initiation to the point where the system seems to undergo no further change, called chemical kinetics. The second deals with the system after all apparent change has stopped, and is called chemical equilibrium. Following those topics we will examine some specific aspects of chemical equilibria involving oxidation-reduction reactions in aqueous solutions and combustion reactions. 

We can now summarize what we have said about the method for balancing oxidation-reduction reactions in aqueous solution ... 

This oxidation-reduction reaction in acidic solution is spontaneous ... 

If you complete and balance the following oxidation-reduction reaction in basic solution... 

---