Thermal decomposition

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For the biological process, see decomposition.

Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes.

The reaction is usually endothermic as heat is required to break chemical bonds in the compound undergoing decomposition. If decomposition is sufficiently exothermic, a positive feedback loop is created producing thermal runaway and possibly an explosion.


CaCO3 → CaO + CO2
The reaction is used to make quick lime, which is an industrially important product.
Engraving of assorted scientific equipment, such as a pneumatic trough. A dead mouse rests under one glass canister.
Equipment used by Priestley in his experiments on gases
  • When water is heated to well over 2000 °C, a small percentage of it will decompose into its constituent elements:
2 H2O → 2 H2 + O2

Decomposition of nitrates, nitrites and ammonium compounds[edit]

Ease of decomposition[edit]

When metals are near the bottom of the reactivity series, their compounds generally decompose easily at high temperatures. This is because stronger bonds form between atoms towards the top of the reactivity series, and strong bonds break less easily. For example, copper is near the bottom of the reactivity series, and copper sulfate (CuSO4), begins to decompose at about 200°C, increasing rapidly at higher temperatures to about 560°C. In contrast potassium is near the top of the reactivity series, and potassium sulfate (K2SO4) does not decompose at its melting point of about 1069°C, nor even at its boiling point.[1]

See also[edit]


  1. ^ Lide, David R. CRC Handbook of Chemistry and Physics, 90th Edition. Publisher: CRC Press 2009. ISBN 978-1420090840