Voltaic cells process

Vaporization Voltaic Cell Process by which a liquid enters the gas phase. A setup that allows a redox reaction to occur spontaneously so that the electrons can be used to do work. 

Similar considerations apply of course to the opposing electromotive forces of polarisation during electrolysis, when the process is executed reversibly, since an electrolytic cell is, as we early remarked, to be considered as a voltaic cell working in the reverse direction. In this way Helmholtz (ibid.) was able to explain the fluctuations of potential in the electrolysis of water as due to the variations of concentration due to diffusion of the dissolved gases. It must not be forgotten, however, that peculiar phenomena—so-called supertension effects—depending on the nature of the electrodes, make their appearance here, and com-... 

Velocity of sound, 146 Virtual change, 92 work, 50 Viscosity, 87 -Vital processes, 35, 70 Voltaic cell, 53, 357, 455... 

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. 

If a voltaic cell is to run spontaneously, the reduction potential at the cathode must be higher (more positive) than the reduction potential at the anode. This will allow the reaction at the anode to proceed as an oxidation (rather than a reduction). The greater the difference in potentials between the cathode and anode, the greater the cell voltage. Eor E° will be positive for spontaneous processes and negative for nonspontaneous ones. 

The wire in the voltaic cell carries the electrons from one half cell to another. The salt bridge allows ions to migrate from one half cell to the other so that there is no buildup of charge as the electrons are transferred from one half cell to the other. The electrodes are the sites of oxidation and reduction in the voltaic cell. These processes will occur on the surfaces of the cathode (electrode where reduction occurs) and the anode (electrode where oxidation occurs). 

In voltaic cells, it is possible to carry out the oxidation and reduction halfreactions in different places when suitable provision is made for transporting the electrons over a wire from one half-reaction to the other and to transport ions from each half-reaction to the other in order to preserve electrical neutrality. The chemical reaction produces an electric current in the process. Voltaic cells, also called galvanic cells, are introduced in Section 17.1. The tendency for oxidizing agents and reducing agents to react with each other is measured by their standard cell potentials, presented in Section 17.2. In Section 17.3, the Nernst equation is introduced to allow calculation of potentials of cells that are not in their standard states. 

P]quations involving electron transftT, such as those given above, are frequently employed in (electrochemistry to represent processes occurring at electrodes, ( ither during ( lectrolysis or in a voltaic cell capable of producing current. It is opportune, therefore, to emphasize their significance at this point an equation sucli as... 

Electrolysis can be useful to clean historic objects recovered from shipwrecks. Coatings of salts from the seawater on metal objects are removed by an electrochemical process. A voltaic cell is set up with a cathode that is the object itself and a stainless steel anode in a basic solution. Chloride ions are removed when the electric current is turned on. 

Describe the process that releases electrons in a zinc-copper voltaic cell. (21.1)... 

Communicating Write two or three sentences describing the processes that take place in a voltaic cell and account for the direction of electron flow. Use the words cathode, anode, oxidation, reduction, and potential difference in your sentences. 

In general, the work that can be obtained in an isothermal change is a maximum when the process is performed in a reversible manner. This is true, for example, in the production of electrical work by means of a voltaic cell. Cells of this type can be made to operate isothermally and reversibly by withdrawing current extremely slowly ( 331) the e.m.f. of a given cell then has virtually its maximum value. On the other hand, if large currents are taken from the cell, so that it functions in an irreversible manner, the E.M.F. is less. Since the electrical work done by the cell is equal to the product of the e.m.f. and the quantity of electricity passing, it is clear that the same extent of chemical reaction in the cell will yield more work in the reversible than in the irreversible operation. 

If the E.M.F. of a voltaic cell is E int. volts, and the process taking place within it is accompanied by the passage of N faradays of electricity, i.e., NF coulombs, where F represents 96,600 int. coulombs, the work done by the cell is NFE int. volt-coulombs, or int. joules (cf. 3b). If the cell is a reversible one, as described above, and E is its reversible, i.e., maximum, E.M.F., at a given temperature and pressure, usually atmospheric, it follows from the arguments presented earlier that... 

We may conclude this brief account of the carbon dioxide assimilation process by describing Baur s carbon dioxide assimilation model To appreciate this, however, it is necessary to say something first about photo-voltaic cells in general... 

Voltage, a measure of the strength of an electric current, represents the force that moves electrons from the anode to the cathode in a voltaic cell. When a greater force (voltage) is applied in the opposite direction, electrons can he pushed from what would normally be the cathode toward the voltaic cell s anode. This process is called electrolysis. In a broader sense, electrolysis is the process by which a redox reaction is made to occur in the nonspontaneous direction. For example, sodium metal reacts readily with chlorine gas to form sodium chloride, but we do not expect sodium chloride, as it sits in our saltshakers, to decompose into sodium metal and chlorine gas. We say the forward reaction below is spontaneous, and the reverse reaction is nonspontaneous. 

Electrolysis The process by which a redox reaction is pushed in the nonspontaneous direction or the process of applying an external voltage to a voltaic cell, causing electrons to move from what would normally be the cell s cathode toward its anode. 

Biological Processes Voltaic Cells A Medical Perspective ... 

A voltaic cell (a) is converted to an electrolytic cell (b) by attaching a battery with a voltage sufficiently large to reverse the reaction. This process underlies commercially available rechargeable batteries. 

By now, you may be thinking that spontaneous electrochemical processes are always beneficial, but consider the problem of corrosion, the natural redox process that oxidizes metals to their oxides and sulfides. In chemical teims, coiTOsion is the reverse of isolating a metal from its oxide or sulfide ore in electrochemical terms, the process shares many similarities with the operation of a voltaic cell. Damage from corrosion to cars, ships, buildings, and bridges runs into tens of billions of dollars annually, so it is a major problem in much of the world. We focus here on the corrosion of iron, but many other metals, such as copper and silver, also conode. 

The most common and economically destructive form of corrosion is the rusting of iron. About 25% of the steel produced in the United States is made just to replace steel already in use that has corroded. Contrary to the simplified equation shown earlier in the text, rust is not a direct product of the reaction between iron and oxygen but arises through a complex electrochemical process. Let s look at the facts of iron corrosion and then use the features of a voltaic cell to explain them ... 

The components of the corrosion process resemble those of a voltaic cell ... 

However, we can make this process happen by supplying from an external source an electric potential greater than eii- In effect, we have converted the voltaic cell into an electrolytic cell and changed the nature of the electrodes—anode is now cathode, and cathode is now anode (Figure 21.23B) ... 

The Example Problems showed you how to use the data from Table 20.1 to calculate the standard potential (voltage) of voltaic cells. Another important use of standard reduction potentials is to determine if a proposed reaction under standard conditions will be spontaneous. How can standard reduction potentials indicate spontaneity Electrons in a voltaic cell always flow from the half-cell with the lower standard reduction potential to the half-cell with the higher reduction potential, giving a positive cell voltage. To predict whether any proposed redox reaction will occur spontaneously, simply write the process in the form of half-reactions and look up the reduction potential of each. Use the values to calculate the potential of a voltaic cell operating with these two half-cell reactions. If the calculated potential is positive, the reaction is spontaneous. If the value is negative, the reaction is not spontaneous. However, the reverse of a nonspontaneous reaction will occur because it will have a positive cell voltage, which means that the reverse reaction is spontaneous. 

---