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By the end of this section, you will be able to:
  • Define electrochemistry and a number of important associated terms
  • Split oxidation-reduction reactions into their oxidation half-reactions and reduction half-reactions
  • Produce balanced oxidation-reduction equations for reactions in acidic or basic solution
  • Identify oxidizing agents and reducing agents

Electricity refers to a number of phenomena associated with the presence and flow of electric charge. Electricity includes such diverse things as lightning, static electricity, the current generated by a battery as it discharges, and many other influences on our daily lives. The flow or movement of charge is an electric current ( [link] ). Electrons or ions may carry the charge. The elementary unit of charge is the charge of a proton, which is equal in magnitude to the charge of an electron. The SI unit of charge is the coulomb (C) and the charge of a proton is 1.602 × 10 −19 C. The presence of an electric charge generates an electric field. Electric current    is the rate of flow of charge. The SI unit for electrical current is the SI base unit called the ampere (A), which is a flow rate of 1 coulomb of charge per second (1 A = 1 C/s). An electric current flows in a path, called an electric circuit    . In most chemical systems, it is necessary to maintain a closed path for current to flow. The flow of charge is generated by an electrical potential difference, or potential, between two points in the circuit. Electrical potential is the ability of the electric field to do work on the charge. The SI unit of electrical potential is the volt (V). When 1 coulomb of charge moves through a potential difference of 1 volt, it gains or loses 1 joule (J) of energy. [link] summarizes some of this information about electricity.

Common Electrical Terms
Quantity Definition Measure or Unit
Electric charge Charge on a proton 1.602 × 10 −19 C
Electric current The movement of charge ampere = A = 1 C/s
Electric potential The force trying to move the charge volt = V = J/C
Electric field The force acting upon other charges in the vicinity
Three photographs are shown in this figure. The first shows lightning against a dark evening sky. The second shows a child at the open base of a green plastic playground tube slide. The child’s hair is sticking up and the child’s shadow on the base of the slide shows the child’s hair sticking up and out in all directions. The final picture shows a 9 volt battery from which red and blue coated wire that is twisted together extend from the battery terminals to the lower region of a yellow platform or board. Above this region are six resistors in a horizontal row, evenly spaced horizontally across the span of the board. Green, blue, and white wires are also visible on the board. 6 orange L E D light bulbs extend from the upper edge of the platform in a horizontal line parallel to the pegs.
Electricity-related phenomena include lightning, accumulation of static electricity, and current produced by a battery. (credit left: modification of work by Thomas Bresson; credit middle: modification of work by Chris Darling; credit right: modification of work by Windell Oskay)

Electrochemistry studies oxidation-reduction reactions, which were first discussed in an earlier chapter, where we learned that oxidation was the loss of electrons and reduction was the gain of electrons. The reactions discussed tended to be rather simple, and conservation of mass (atom counting by type) and deriving a correctly balanced chemical equation were relatively simple. In this section, we will concentrate on the half-reaction method for balancing oxidation-reduction reactions. The use of half-reactions is important partly for balancing more complicated reactions and partly because many aspects of electrochemistry are easier to discuss in terms of half-reactions. There are alternate methods of balancing these reactions; however, there are no good alternatives to half-reactions for discussing what is occurring in many systems. The half-reaction method    splits oxidation-reduction reactions into their oxidation “half” and reduction “half” to make finding the overall equation easier.

Practice Key Terms 6

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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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