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Chemical decomposition caused by heat

the biological process

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 or other chemical reaction.

Ammonium dichromate on heating yields nitrogen, water and chromium(III) oxide. Ammonium nitrate on strong heating yields dinitrogen oxide ("laughing gas") and water. Ammonium nitrite on heating yields nitrogen gas and water. Barium azide on heating yields barium metal and nitrogen gas. Sodium azide on heating at violently decomposes to nitrogen and metallic sodium. Sodium nitrate on heating yields sodium nitrite and oxygen gas. Organic compounds like tertiary amines on heating undergo Hofmann elimination and yield secondary amines and alkenes.

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 are difficult to break. For example, copper is near the bottom of the reactivity series, and copper sulfate (CuSO4), begins to decompose at about , increasing rapidly at higher temperatures to about In contrast potassium is near the top of the reactivity series, and potassium sulfate (K2SO4) does not decompose at its melting point of about , nor even at its boiling point.

Many scenarios in the real world are affected by thermal degradation. One of the things affected is fingerprints. When anyone touches something, there is residue left from the fingers. If fingers are sweaty, or contain more oils, the residue contains many chemicals. De Paoli and her collogues conducted a study testing thermal degradation on certain components found in fingerprints. For heat exposure, the amino acid and urea samples started degradation at and for lactic acid, the decomposition process started around These components are necessary for further testing, so in the forensics discipline, decomposition of fingerprints is significant.