![]() ![]() A galvanic (voltaic) cell An electrochemical cell that uses the energy released during a spontaneous oxidation–reduction (redox) reaction ( Δ G 0 ) oxidation–reduction (redox) reaction. There are two types of electrochemical cells: galvanic cells and electrolytic cells. An apparatus that is used to generate electricity from a spontaneous redox reaction or, conversely, that uses electricity to drive a nonspontaneous redox reaction is called an electrochemical cell An apparatus that generates electricity from a spontaneous oxidation–reduction (redox) reaction or, conversely, uses electricity to drive a nonspontaneous redox reaction. As the reaction progresses, the electrons flow from the reductant to the oxidant over this electrical connection, producing an electric current that can be used to do work. With redox reactions, however, it is possible to physically separate the oxidation and reduction half-reactions in space, as long as there is a complete circuit, including an external electrical connection, such as a wire, between the two half-reactions. Acid–base reactions, for example, are usually carried out with the acid and the base dispersed in a single phase, such as a liquid solution. In most of our discussions of chemical reactions, we have assumed that the reactants are in intimate physical contact with one another. In any redox reaction, the number of electrons lost by the reductant equals the number of electrons gained by the oxidant. For the reaction of zinc with bromine, the overall chemical reaction is as follows: (For more information on valence electrons, see Chapter 7 "The Periodic Table and Periodic Trends", Section 7.3 "Energetics of Ion Formation".)īecause it is impossible to have a reduction without an oxidation and vice versa, a redox reaction can be described as two half-reactions Reactions that represent either the oxidation half or the reduction half of an oxidation–reduction (redox) reaction., one representing the oxidation process and one the reduction process. The associated potential energy is determined by the potential difference between the valence electrons in atoms of different elements. is the species that gains electrons and is reduced in the process. is the substance that loses electrons and is oxidized in the process the oxidant A substance that is capable of accepting electrons and in the process is reduced. The reductant A substance that is capable of donating electrons and in the process is oxidized. ![]() As we described in Chapter 3 "Chemical Reactions", a redox reaction occurs when electrons are transferred from a substance that is oxidized to one that is being reduced. In any electrochemical process, electrons flow from one chemical substance to another, driven by an oxidation–reduction (redox) reaction. To distinguish between galvanic and electrolytic cells. ![]()
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