Electrochemistry

Electrochemistry is the branch of chemistry concerned with the relationship between electricity and chemical change. Its reactions are oxidation-reduction, or redox, reactions, in which electrons are transferred between substances. Oxidation is the loss of electrons and reduction is the gain of electrons; the two always occur together, because the electrons released by one substance must be taken up by another. By separating the two halves of such a reaction, electrochemistry allows the flow of electrons to be used as, or driven by, an electric current.

An electrochemical cell is the basic apparatus, consisting of two electrodes immersed in an electrolyte, a solution or medium that conducts ions. In a galvanic, or voltaic, cell a spontaneous redox reaction generates an electric current, which is the principle behind batteries and fuel cells. In an electrolytic cell the reverse occurs: an external electric current is supplied to force a non-spontaneous reaction to take place. Electrolysis of this kind is used industrially to extract and purify metals and to deposit thin metal coatings, as in nickel electroplating.

Electrochemical processes are central to many practical technologies. Batteries store chemical energy and release it as electricity, while fuel cells produce electricity continuously from a supplied fuel such as hydrogen. Corrosion, including the rusting of iron, is itself an electrochemical process in which a metal is oxidised, and understanding it guides methods of protection. Electrochemical methods are also widely used in chemical analysis to measure concentrations and study reactions.

Frequently asked questions

What is a redox reaction?

A redox reaction is one in which electrons are transferred between substances. One substance is oxidised, losing electrons, while another is reduced, gaining them. The two always happen together.

How does a battery relate to electrochemistry?

A battery is a galvanic cell. A spontaneous redox reaction inside it pushes electrons through an external circuit, turning stored chemical energy into electric current.

What is the difference between a galvanic and an electrolytic cell?

A galvanic cell produces electricity from a spontaneous reaction. An electrolytic cell uses an external electric current to drive a reaction that would not occur on its own.