Chemical Decomposition Reaction

Overview of a Chemical Decomposition or Analysis Reaction

In a decomposition reactions, compounds are broken into simpler forms.
In a decomposition reactions, compounds are broken into simpler forms. John Smith / Getty Images

A chemical decomposition reaction or analysis reaction is one of the most common types of chemical reactions. In a decomposition reaction a compound is broken into smaller chemical species.
AB → A + B

In some cases, the reactant breaks into its component elements, but a decomposition may involve breakdown into any smaller molecules. The process may occur in a single step or multiple ones.

Because chemical bonds are broken, a decomposition reaction requires the addition of energy to begin. Usually the energy is supplied as heat, but sometimes simply a mechanical bump, electric shock, radiation, or change in humidity or acidity initiates the process. The reactions may be classified on this basis as thermal decomposition reactions, electrolytic decomposition reactions, and catalytic reactions.

A decomposition is the opposite or reverse process of a synthesis reaction.

Decomposition Reaction Examples

The electrolysis of water into oxygen and hydrogen gas is an example of a decomposition reaction:
2 H2O → 2 H2 + O2

Another example is the decomposition of potassium chloride into potassium and chlorine gas.

2 KCl(s) → 2 K(s) + Cl2(g)

Uses of Decomposition Reactions

Decomposition reactions are also called analysis reactions because they are extremely valuable in analytical techniques. Examples include mass spectrometry, gravimetric analysis, and thermogravimetric analysis.


  • Brown, T.L.; LeMay, H.E.; Burston, B.E. (2017). Chemistry: The Central Science (14th ed.). Pearson. ISBN:9780134414232.
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Helmenstine, Anne Marie, Ph.D. "Chemical Decomposition Reaction." ThoughtCo, Apr. 5, 2023, Helmenstine, Anne Marie, Ph.D. (2023, April 5). Chemical Decomposition Reaction. Retrieved from Helmenstine, Anne Marie, Ph.D. "Chemical Decomposition Reaction." ThoughtCo. (accessed May 30, 2023).