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Chemical decomposition, analysis or breakdown is the separation of a chemical compound into elements or simpler compounds. It is sometimes defined as the exact opposite of a chemical synthesis. Chemical decomposition is often an undesired chemical reaction. The stability that a chemical compound ordinarily has is eventually limited when exposed to extreme environmental conditions like heat, radiation, humidity or the acidity of a solvent. The details of decomposition processes are generally not well defined, as a molecule may break up into a host of smaller fragments. Chemical decomposition is exploited in several analytical techniques, notably mass spectrometry, traditional gravimetric analysis, and thermogravimetric analysis.
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A broader definition of the term decomposition also includes the breakdown of one phase into two or more phases.
There are six types of decomposition reactions, three of which are considered broad types. They are the thermal, electrolytic and catalytic thermal types of decomposition reactions. It is the latter three which are discussed here.
Reaction formula
The generalized reaction for chemical decomposition is:
AB → A + B with a specific example being the electrolysis of water to gaseous hydrogen and oxygen:2 H2O(I) → 2 H2 + O2Additional examples
An example of spontaneous decomposition is that of hydrogen peroxide, which will slowly decompose into water and oxygen:
2 H2O2 → 2 H2O + O2Carbonates will decompose when heated, a notable exception being that of carbonic acid, H2CO3. Carbonic acid, the "fizz" in sodas, pop cans and other carbonated beverages, will decompose over time (spontaneously) into carbon dioxide and water
H2CO3 → H2O + CO2Other carbonates will decompose when heated producing the corresponding metal oxide and carbon dioxide. In the following equation M represents a metal:
MCO3 → MO + CO2A specific example of this involving calcium carbonate:
CaCO3 → CaO + CO2Metal chlorates also decompose when heated. A metal chloride and oxygen gas are the products.
2 MClO3 → 2 MCl + 3 O2A common decomposition of a chlorate to evolve oxygen utilizes potassium chlorate as follows:
2 KClO3 → 2 KCl + 3 O2