Upon completion of this topic, learners will be able to:

• define a redox reaction;
• define oxidation and reduction in terms of electron transfer and change in oxidation number;
• describe the oxidizing and reducing agents;
• identify the species that are oxidized and reduced in a given redox reaction and determine the oxidizing and reducing agents;
• balance a given redox reaction, using the change in oxidation-number method; and
• balance a given redox reaction, using the ion-electron method.

Electrochemistry is best defined as the study of the interchange of chemical and electrical energy. It is primarily concerned with two processes that involve oxidation–reduction reactions: the generation of an electric current from a spontaneous chemical reaction and the opposite process, the use of a current to produce chemical change. The reactions involve electron transfer, and so they are oxidation-reduction (or redox) reactions. Many metals can be purified or electroplated using electrochemical methods. Devices such as automobiles, smartphones, electronic tablets, watches, pacemakers, and many others use batteries for power.