Batteries voltaic cell

Any self-contained unit having a specific functional purpose, as (a) voltaic cell (battery) to generate electric current, (b) electrolytic cell to effect electrolysis, (c) fuel cell to convert chemical energy into electricity, and (d) solar cell to capture heat from sunlight. All except the last involve use of electrodes and electrolytes. 

SECTION 20.7 A battery is a self-contained electrochemical power source that contains one or more voltaic cells. Batteries are based on a variety of different redox reactions. Several common batteries were discussed. The lead-acid battery, the nickel-cadmium battery, the nickel-metal-hydride battery, and the lithium-ion battery are examples of rechargeable batteries. The common alkaline dry cell is not rechargeable. Fuel cells are voltaic cells that utilize redox reactions in which reactants such as H2 have to be continuously supplied to the cell to generate voltage. 

We have seen that we can combine the electron-losing tendency of one substance with the electron-gaining tendency of another to create electrical current in a voltaic cell. Batteries are voltaic cells conveniently packaged to act as portable sources of electricity. The actual oxidation and reduction reactions depend on the particular type of battery. In this section, we examine several different types. 

The reactions occurring in voltaic cells (batteries) are important sources of electricity, but similar reactions also underlie corrosion processes. First, we will consider the electrochemical basis of corrosion, and then we will see how electrochemical principles can be applied to control corrosion. 

The rechargeable 12-V lead storage battery used in automobiles consists of six voltaic cells of the type shown in Figure 18.12. A group of lead plates, the grids of which are filled... 

There are two types of cells electrolytic (which requires a battery or external power source) and voltaic (which requires no battery or external power source). The reaction in the diagram is voltaic and therefore spontaneous. In a voltaic cell, the anode is the negative terminal, and oxidation occurs at the anode. Remember the OIL portion of OIL RIG (Oxidation Is Losing electrons) and AN OX (ANode is where Oxidation occurs). 

Galvanic cells are named after the Italian doctor Luigi Galvani (1737-1798), who generated electricity using two metals. These cells are also called voltaic cells, after the Italian physicist Count Alessandro Volta (1745-1827), who built the first chemical batteries. 

Have you ever wondered how a battery works You can find out how in this chapter. In Chapter 11, you learned how oxidation-reduction reactions transfer electrons from one species to another. Batteries use oxidation-reduction reactions, but they are carefully designed so the flow of electrons takes place through a conducting wire. The first battery was made in 1796 by Alessandro Volta, and batteries are commonly called voltaic cells in his honor. There are many different ways to construct a voltaic cell, but in all cases, two different chemical species must be used. The voltage of the cell depends on which species are used. 

Electrodes in a voltaic cell, however, are connected to circuits— paths by which electrons flow. Voltaic cells are sources of electricity, so they can be used to drive electrolytic reactions or perform other activities that require electricity. The term voltaic honors the Italian scientist Alessandro Volta (1745-1827), a pioneer of electrochemistry. A simple voltaic cell can form a battery, invented by Volta in 1800. The unit of electric potential, the volt, also honors Volta. 

Electrons created in the oxidation reaction at the anode of a voltaic cell flow along an external circuit to the cathode, where they fuel the reduction reaction taking place there. We use the spontaneous reaction between zinc and copper as an example of a voltaic cell here, but you should realize that many powerful redox reactions power many types of batteries, so they re not limited to reactions between copper and zinc. 

These voltaic cells can t run forever, however. The loss of mass at the zinc anode will eventually exhaust the supply of zinc, and the redox reaction won t be able to continue. This phenomenon is why most batteries run out over time. Rechargeable batteries take advan-tc e of a reverse reaction to resupply the anode, but many redox reactions don t allow for this, so rechargeable batteries must be made of very specific reactants. 

Secondary cells are voltaic cells that can be recharged repeatedly. The lead storage battery and nickel-cadmium cell are examples of secondary cells. The lead storage battery consists of six voltaic cells. Its electrodes are lead alloy plates, which take the form of a grill, filled with spongy lead metal. The cathode consists of another group of plates filled with lead (IV) oxide, P6O2. Dilute sulfuric acid is the electrolyte of the cell. When the battery delivers a current, the lead is oxidized to lead ions, which combine with sulfate fS0 7 ions of the electrolyte to cover the lead electrode. 

It is in accordance with facts as I see them to compare the chemical action of light with that of a voltaic cell. Light separates the constituents of many ponderable compounds and forces them to form new compounds. . . just as the poles of a voltaic battery do to a still greater extent. 

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. 

A battery (or galvanic or voltaic cell) is a device that uses oxidation and reduction reactions to produce an electric current. In an electrolytic cell, an external source of electric current is used to drive a chemical reaction. This process is called electrolysis. When the electric potential applied to an electrochemical cell is just sufficient to balance the potential produced by reactions in the cell, we have an electrochemical cell at equilibrium. This state also occurs if there is no connections between the terminals of the cell (open-circuit condition). Our discussion in this chapter will be limited to electrochemical cells at equilibrium. 

Because redox reactions can make electrons move from one substance to another it is possible to create a setup so that the electrical energy produced in a redox reaction can be channeled to do work. There is a way to harvest the electrons produced by a redox reaction. Today these devices are called batteries. The first device that could do this was called a voltaic cell. In a voltaic cell a redox reaction occurs spontaneously so that the electrons can be used to do work. A typical voltaic cell is shown in Figure 10.1. 

Ordinary batteries (voltaic cells) for flashlights, radios, and so on many are Leclanche cells. 

This type of cell essentially operates like a simple battery, with many diverse applications, and it is anticipated that such voltaic cells could be charged by the human body to provide a future power source for implanted medical devices such as heart pacemakers. 

There is another way in which electrons can be rearranged in a chemical reaction, and that is through a wire. Electrochemistry is redox chemistry wherein the site for oxidation is separated from the site for reduction. Electrochemical setups basically come in two flavors electrolytic and voltaic (also known as galvanic) cells. Voltaic cells are cells that produce electricity, so a battery would be classed as a voltaic cell. The principles that drive voltaic cells are the same that drive all other chemical reactions, except the electrons are exchanged though a wire rather than direct contact. The reactions are redox reactions (which is why they produce an electron current) the reactions obey the laws of thermodynamics and move toward equilibrium (which is why batteries run down) and the reactions have defined rates (which is why some batteries have to be warmed to room temperature before they produce optimum output). 

The reaction in the lemon battery is the reduction of copper ions (a little bit of copper dissolves from the copper penny in the acidic lemon juice) and the oxidation of zinc into zinc ions—the thermodynamically more stable state. Because the reaction is moving toward a more stable state, it can produce electricity as a voltaic cell. An electrolytic cell is the antithesis of the voltaic cell. In the voltaic cell, a chemical reaction is used to produce electricity. In an electrolytic cell, electricity is used to produce chemistry. A demonstration electrolytic cell can be set up as follows. 

Batteries are voltaic cells packaged in a compact, usable form. 

Since various authors have referred to the electrochemical mechanism occurring around ore bodies as a geobattery or natural voltaic cell, it is appropriate to introduce the concept of voltaic cells. Voltaic cells are man-made electrical circuits in which the impetus for current flow comes directly from the chemical energy of partially-separated reactants within the cell. All batteries are voltaic cells. 

An electrolytic cell is similar to a voltaic cell except the electrochemical reactions involved do not occur spontaneously but require the input of current from an external source. Wires connected to each end of a battery and submerged in a suitable electrolyte can represent an electrochemical cell. As with voltaic cells, the creation and/or removal of ions at the electrodes facilitates the transfer of current into and out of solution. If the electrolytes in solution are redox-inert within the stability field of water (e.g., Na and Cf) and the voltage is over 1.2 volts, the hydrolysis of water may transfer current at the electrodes ... 

Luigi Galvani (1791) was the first to discover the physiological action of electricity. He demonstrated the existence of bioelectric forces in animal tissue. His experiments led Alessandro Volta to the invention of the first battery, voltaic pile [8]. In 1800, Alessandro Volta described the voltaic pile in a letter to the Royal Society in London [7]. The original voltaic cell used two metal disks as electrodes, namely zinc and silver. Cardboard disks separated the electrodes and seawater was the electrolyte. A current was produced when the silver disk was connected to the zinc disk through an external wire. The voltaic pile established the foundation for the liquid battery type. Many other metals and electrolytes have been tried during the last two centuries [9]. 

See dry cell storage battery voltaic cell fuel cell solar cell intercalation compound. 

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