Releasing Energy through Reactions in Batteries

Releasing Energy through Reactions in Batteries

Reactions that involve a change in oxidation number are called

oxidation-reduction reactions. An element is oxidized if the oxidation number

has become more positive in value. The term reduction

describes the opposite process, in which the oxidation number becomes more

negative in value. In the same equation, for example, the hydrogen is reduced.

The oxidation number has changed from +1 to 0. If everything is counted

through the entire equation, oxidation and reduction are equal and balance to

0.

When electric energy is needed, batteries and fuel cells are one way to

provide it. A battery chemically stores and then releases energy. A fuel cell

converts energy produced by a chemical reaction directly into usable power.

Batteries range in size from single-cell models smaller than coins to

multi-cell units that fill large rooms. Portable radios, pocket calculators, watches,

and hearing aids are typical devices powered by batteries. Very large battery

installations supply standby energy for equipment such as that in telephone

exchanges.

Alessandro Volta, an Italian professor, devised the first battery in 1800 to

provide steady electric current for study and practical use. Before that time,

only static electricity--a novelty with no practical value--could be produced.

Batteries are either primary or secondary. A primary battery produces its

energy by consuming one of the chemicals it contains. When the chemical is

gone, the battery no longer produces energy and must be replaced. The

carbon-zinc batteries used in flashlights and tape recorders are primary.

Secondary batteries, or storage batteries, obtain energy by transforming certain

kinds of chemicals ...

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...mation of a green patina, or film, called

verdigris, which is composed of copper carbonate. In many instances buildings

with copper-clad roofs and trim are deliberately allowed to develop patinas

because the color is considered attractive.

Corrosion takes place at a much faster rate in heavily industrialized areas

that have high levels of sulfur and nitrogen pollutants in the atmosphere. These

compounds combine with moisture in the air to produce extremely corrosive

acids.

Metals may be protected from corrosion by coating them. A variety of coating

processes are used, including painting, electroplating with chromium, or plating

with zinc, which is called galvanizing. Alloying steel with chromium or chromium

and nickel produces stainless steel, which is resistant to rusting. Plastics,

ceramics, and certain rubber compounds are also used to coat metals.