Electrical energy oxidation-reduction reactions

The chemical process that produces an electrical current from chemical energy is called an oxidation-reduction reaction. The oxidation-reduction reaction in a battery involves the loss of electrons by one compound (oxidation) and the gain of electrons (reduction) by another compound. Electrons are released from one part of the batteiy and the external circuit allows the electrons to flow from that part to another part of the batteiy. In any battery, current flows from the anode to the cathode. The anode is the electrode where positive current enters the device, which means it releases electrons to the external circuit. The cathode, or positive terminal of the battery, is where positive current leaves the device, which means this is where external electrons are taken from the external circuit. 

Electron-transfer reactions occur all around us. Objects made of iron become coated with mst when they are exposed to moist air. Animals obtain energy from the reaction of carbohydrates with oxygen to form carbon dioxide and water. Turning on a flashlight generates a current of electricity from a chemical reaction in the batteries. In an aluminum refinery, huge quantities of electricity drive the conversion of aluminum oxide into aluminum metal. These different chemical processes share one common feature Each is an oxidation-reduction reaction, commonly called a redox reaction, in which electrons are transferred from one chemical species to another. 

What are oxidation-reduction reactions How are they involved in the interconversion of chemical and electrical energy ... 

If one takes a spontaneous electron-transfer reaction and separates the materials undergoing oxidation and reduction, allowing the electron transfer to occur through a good conductor such as a copper wire, a battery is created. By proper design, the electrical energy associated with reactions of this type can be harnessed. The fields of electrochemistry (e.g., batteries) and pyrotechnics (e.g., fireworks) are actually very close relatives. The reactions involved in the two areas can look strikingly similar ... 

Electrochemistry is the study of the relationship between electrical energy and chemical change. It involves oxidation-reduction reactions to produce electricity, or electricity to cause an oxidation-reduction reaction. 

Thus, if we start with our reactants and products under standard conditions and allow the reaction to proceed to equilibrium, an amount of energy AG° becomes available for external work. In the context of doing external electrical work, an oxidation—reduction reaction can generate a standard electromotive force AE° given by... 

Virtually all energy transductions in cells can be traced to this flow of electrons from one molecule to another, in a downhill flow from higher to lower electrochemical potential as such, this is formally analogous to the flow of electrons in a battery-driven electric circuit. All these reactions involving electron flow are oxidation-reduction reactions one reactant is oxidized (loses electrons) as another is reduced (gains electrons). 

So we see that with the proper setup it is possible to harness electrical energy from an oxidation-reduction reaction. The apparatus shown in Figure 11.8 is one example. Such devices are called voltaic cells. Instead of two containers, a voltaic cell can be an all-in-one, self-contained unit, in which case it is called a battery. Batteries are either disposable or rechargeable, and here we explore some examples of each. Although the two types differ in design and composition, they function by the same principle two materials that oxidize and reduce each other are connected by a medium through which ions travel to balance an external flow of electrons. 

Disposable batteries have relatively short lives because electron-producing chemicals are consumed. The main feature of rechargeable batteries is the reversibility of the oxidation and reduction reactions. In your car s rechargeable lead storage battery, for example, electrical energy is produced as lead dioxide, lead, and sulfuric acid are consumed to form lead sulfate and water. The elemental lead is oxidized to Pb2+, and the lead in the lead dioxide is reduced from the Pb4+ state to the Pb2+ state. Combining the two half-reactions gives the complete oxidation-reduction reaction ... 

The transfer of a single electron between two chemical entities is the simplest of oxidation-reduction processes, but it is of central importance in vast areas of chemistry. Electron transfer processes constitute the fundamental steps in biological utilization of oxygen, in electrical conductivity, in oxidation reduction reactions of organic and inorganic substrates, in many catalytic processes, in the transduction of the sun s energy by plants and by synthetic solar cells, and so on. The breadth and complexity of the subject is evident from the five volume handbook Electron Transfer in Chemistry (V. Balzani, Ed.), published in 2001. The most fimdamental principles that govern the efficiencies, the yields or the rates of electron-transfer processes are independent of the nature of the substrates. The properties of the substrates do dictate the conditions for apphcability of those fimdamental... 

A battery is a complex device that delivers electrical energy by transforming chemical energy. The electrical energy is provided by electrochemical reactions (oxidation-reduction reactions) that take place at the anode and the cathode of the battery. While the term battery is often used, the basic electrochemical unit being referred to is the cell [1]. A battery is composed of several cell units that are connected in series or in parallel... 

We learn much about chemical reactions from the study of electrochemistry. The amount of electrical energy consumed or produced can be measured quite accurately. All electrochemical reactions involve the transfer of electrons and are therefore oxidation-reduction reactions. The sites of oxidation and reduction are separated physically so that oxidation occurs at one location, and reduction occurs at the other. Electrochemical processes require some method of introducing a stream of electrons into a reacting chemical system and some means of withdrawing electrons. In most applications the reacting system is contained in a cell, and an electric current enters or exits by electrodes. 

Electrochemistry is the branch of chemistry that deals with the interconversion of electrical energy and chemical energy. Electrochemical processes are redox (oxidation-reduction) reactions in which the energy released by a spontaneous reaction is converted to electricity or in which electrical energy is nsed to cause a nonspontaneous reaction to occur. Although redox reactions were discnssed in Chapter 4, it is helpful to review some of the basic concepts that will come np again in this chapter. 

A fundamental understanding of oxidation-reduction reactions is vital to the inorganic chemist in contexts ranging from energy transduction - chemical to electrical and the converse, in technical matters in corrosion processes and metallurgy, redox processes in environmental chemistry and metalloenzymes and metallo-proteins involved in electron transfer. Electron-transfer reactions of transition metal complexes are accompanied by a change in the oxidation state of the metal... 

A battery is a collection of one or more electrochemical cells that convert chemical energy into electrical energy via electrochemical reactions (oxidation-reduction reactions). These reactions take place at the battery s anode and cathode. The electrochemical cells are connected in series or in parallel depending on the desired voltage and capacity. Series connections provide a higher voltage, whereas parallel connections provide a higher capacity, compared with one cell. 

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