Cell, voltaic

A voltaic cell produces electrical energy through spontaneous redox chemical reactions. When zinc metal is placed in a solution of copper sulfate, an electron transfer takes place between the zinc metal and copper ions. The driving force for the reaction is the greater attraction of the copper ions for electrons ... 

Italian physicist Alessandro Volta demonstrates the galvanic cell, also known as the voltaic cell. 

Anion a negatively charged ion it migrates to the anode of a galvanic or voltaic cell. 

Anode the electrode in a galvanic or voltaic cell at which electrochemical oxidation takes place. 

Voltaic Cell a term sometimes used for an electrochemical cell it is sometimes used to refer to a cell in which chemical changes are caused by the application of an external e.m.f. 

The principles discussed in this chapter have a host of practical applications. Whenever you start your car, turn on your cell phone, or use a remote control for your television or other devices, you are making use of a voltaic cell. Many of our most important elements, including hydrogen and chlorine, are made in electrolytic cells. These applications, among others, are discussed in Section 18.6. ... 

In principle at least, any spontaneous redox reaction can serve as a source of energy in a voltaic cell. The cell must be designed in such a way that oxidation occurs at one electrode (anode) with reduction at the other electrode (cathode). The electrons produced at the anode must be transferred to the cathode, where they are consumed. To do this, the electrons move through an external circuit, where they do electrical work. 

To understand how a voltaic cell operates, let us start with some simple cells that are readily made in the general chemistry laboratory. 

To design a voltaic cell using the Zn-Cu2+ reaction as a source of electrical energy, the electron transfer must occur indirectly that is, the electrons given off by zinc atoms must be made to pass through an external electric circuit before they reduce Cu2+ ions to copper atoms. One way to do this is shown in Figure 18.2. The voltaic cell consists of two half-cells—... 

A Zn-Cu + voltaic cell. In this voltaic cell, a voltmeter (left) is connected to a half-cell consisting of a Cu cathode in a solution of blue Cu2+ ions and a half-cell consisting of a Zn anode in a solution of colorless Zn2+ ions. The following spontaneous reaction takes place in this cell Zn(s) + Ctf+lag) — M+(atfl + Cu(s). 

This reaction, like that between Zn and Cu2+, can serve as a source of electrical energy in a voltaic cell The cell is similar to that shown in Figure 18.2 except that, in the anode compartment, a nickel electrode is surrounded by a solution of a nickel(II) salt, such as NiCl2 or NiS04. The cell notation is Ni Ni2+ Cu2+ Cu. 

A voltaic cell using this reaction is similar to the Zn-Cu2+ cell the Zn Zn2+ half-cell and the salt bridge are the same. Because no metal is involved in the cathode half-reaction, an inert electrode that conducts an electric current is used. Frequently, the cathode is made of platinum (Figure 18.3, p. 484). In the cathode, Co3+ ions are provided by a solution of Co(N03)3. The half-reactions occurring in the cell are... 

A Zn-Co3+ voltaic cell. A platinum electrode is immersed in a solution containing Co3+ and Co2+ ions.The spontaneous cell reaction is... 

To summarize our discussion of the structure of voltaic cells, note that—... 

The driving force behind the spontaneous reaction in a voltaic cell is measured by the cell voltage, which is an intensive property, independent of the number of electrons passing through the cell. Cell voltage depends on the nature of the redox reaction and the concentrations of the species involved for the moment, we ll concentrate on the first of these factors. 

Click Coached Problems for a self-study module on voltaic cell potentials. 

The calculated voltage, E°, is always a positive quantity for a reaction taking place in a voltaic cell... 

When a voltaic cell operates, supplying electrical energy, the concentration of reactants decreases and that of the products increases. As time passes, the voltage drops steadily. Eventually it becomes zero, and we say that the cell is dead. At that point, the redox reaction taking place within the cell is at equilibrium, and there is no driving force to produce a voltage. 

Consider a voltaic cell in which the following reaction occurs... 

The overall reaction occurring in this voltaic cell is... 

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... 

A fuel cell is a voltaic cell in which a fuel, usually hydrogen, is oxidized at the anode. At the cathode, oxygen is reduced. The reaction taking place in the alkaline fuel cells used in the space program since the 1960s is... 

Draw a diagram for a voltaic cell, labeling electrodes and direction of current flow. (Example 18.1 Problems 3-8) Questions and Problems assignable in OWL 2,6... 

A voltaic cell consists of two half-cells. One of the half-cells contains a platinum electrode surrounded by chromium(III) and dichromate ions. The other half-cell contains a platinum electrode surrounded by bromate ions and liquid bromine. Assume that the cell reaction, which produces a positive voltage, involves both chromium(III) and bromate ions. The cell is at 25°C. Information for the bromate reduction half reaction is as follows ... 

Consider a salt bridge voltaic cell represented by the following reaction ... 

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