Oxidation-reduction reactions electron movement

Reactions in which there is a change in the charges of some or all of the reactants are called oxidation-reduction (redox) reactions. Because there are changes in charge, equations can be considered with the inclusion of electrons showing the movement of electrons from one participant in the reaction to another. The reaction of metallic copper and sulfur is an example of an oxidation-reduction reaction. 

The half-reaction method is a way of balancing oxidation-reductions reactions by the recognition of oxidation and reduction with separate reactions. Included in the reactions are the number of electrons that move and the nature of movement (gain or loss). The steps for this technique are ... 

In other membranes responsible for energy transduction, oxidation-reduction reactions are the basis for proton movement across the membrane. The classical example is found in mitochondria where electron flow through the respiratory system drives proton movement from the inner matrix to the intermembrane space. The resultant protonmotive force is used to drive ATP synthesis or to maintain mitochondrial membrane potential (negative inside). A similar association between electron transport in a membrane oxidation reduction chain and proton movement... 

The energy released by electron transfer can be used in the transport of protons through the membrane. One of the proton conduction mechanisms in proteins is through a chain of hydrogen bonds in the protein, i.e. a Grotthus mechanism (Section 2.9), similar to the mechanism of proton movement in ice. Protons are injected and removed by the various oxidation/reduction reactions which occur in the cell there is no excess of protons or electrons in the final balance, and the reaction cycle is self-sustaining. 

One of the main purposes for using oxidation numbers is to follow the movement of electrons during an oxidation-reduction reaction. Doing so helps to predict the products and determine the outcomes of such reactions. There are a few different ways to analyze redox reactions, but we will focus on only one the ion-electron method (also called the half-reaction method). The procedure requires that you know the reactants and products of the reaction, but, by going through the process, you will gain a better understanding of the mechanisms by which these reactions proceed. 

Chemists use some important terminology to describe the movement of electrons in oxidation-reduction reactions. Oxidation is the loss of electrons, and reduction is the gain of electrons. (The original meaning of reduction comes from the process of reducing large amounts of metal ore to smaller amounts of metal, but you ll see shortly why we use the term reduction for the act of gaining.)... 

One of the tenets of the chemiosmotic theory is that energy from the oxidation-reduction reactions of the electron transport chain is used to transport protons from the matrix to the intermembrane space. This proton pumping is generally facilitated by the vectorial arrangement of the membrane spanning complexes. Their stracture allows them to pick up electrons and protons on one side of the membrane and release protons on the other side of the membrane as they transfer an electron to the next component of the chain. The direct physical link between proton movement and electron transfer can be illustrated by an examination of the Q cycle for the b-Ci complex (Fig. 21.9). The Q cycle involves a double cycle of CoQ reduction and oxidation. CoQ accepts two protons at the matrix side together with two electrons it then releases protons into the intermembrane space while donating one electron back to another component of the cytochrome b-Ci complex and one to cytochrome c. 

Due to the movement of electrons created by this reaction at both electrodes, current will flow. The diffusion coefficient of oxygen is slower than the oxidation-reduction reaction at the electrode. The steady-state current /, which is proportional to the diffusion coefficient of oxygen, can be expressed in microamperes by the following equation ... 

They are the basis of many products and processes, from batteries to photosynthesis and respiration. You know redox reactions involve an oxidation half-reaction in which electrons are lost and a reduction half-reaction in which electrons are gained. In order to use the chemistry of redox reactions, we need to know about the tendency of the ions involved in the half-reactions to gain electrons. This tendency is called the reduction potential. Tables of standard reduction potentials exist that provide quantitative information on electron movement in redox half-reactions. In this lab, you will use reduction potentials combined with gravimetric analysis to determine oxidation numbers of the involved substances. 

During reduction, electrons travel/rom the power pack, through the electrode, transfer across the electrode-solution interface and enter into the electroactive species in solution. Conversely, during oxidation, electrons move in the opposite direction, and are conducted away from the electroactive material in solution and across the electrode-solution interface as soon as the electron-transfer reaction occurs. (Incidentally, these different directions of electron movement explains why an oxidative current has the opposite sign to a reductive current, cf. Section 1.2.)... 

Everything important that happens in the body is directly related to electrons being moved from place to place to make things happen. Electron transfer is the basis for all oxidation and reduction reactions, including cellular respiration—the making of energy. Electrolytes are the top enzyme activators and are essential to the movement of nerve messages in the body and protection of the heart muscle and blood vessels. 

Oxidation-reduction (redox) reactions Involve the movement of electrons. The half-reaction method of balancing a redox reaction separates the overall reaction into two half-reactions. This reflects the actual separation of the two half-cells in an electrochemical cell... 

Whether an electrochemical process releases or absorbs free energy, it always involves the movement of electrons from one chemical species to another in an oxidation-reduction (redox) reaction. In this section, we review the redox process and describe the half-reaction method of balancing redox reactions. Then we see how such reactions are used in electrochemical cells. 

In order for electrons to be transferred from the reductant to the oxidant, the oxidant must have a greater affinity for electrons than the reductant does. The standard reduction potential, EO is a measure of the affinity of a molecule (or partial reaction) for electrons measured at pH 7 and 25 C. Table 15.1 shows standard reduction potentials for several reactions/species of interest in biochemistry. Species with a higher standard reduction potential tend to accept electrons from molecules with a lower standard reduction potential. Thus, electrons tend to move from cytochrome c(+2) to Cytochrome a (+3), because EO = 0.25 volts for the cytochrome c(+2) half-reaction whereas EO = 0.29 volts for the cytochrome a(+3) half-reaction. Keep in mind, though, that the movement of electrons from one compound to another based on EO values is only a tendency. If equal concentrations of the various species are present, the EO tells the direction electrons will flow. At other concentrations, the free energy change for the process (see below) must be calculated to determine the direction of electron movement. 

The oxidation and reduction of conducting polymers relies on both ion and electron movement. Smela has developed an experimental system designed to make ion transport the rate-limiting step and has studied the reduction reaction in PPy(DBS) (Figure 15.2). 

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