Chemical decomposition



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.

A broader definition of the term decomposition also includes the breakdown of one phase into two or more phases.

There are broadly three types of decomposition reactions: thermal, electrolytic and catalytic.

Reaction formula
The generalized reaction for chemical decomposition is:


 * AB &rarr; A + B

with a specific example being the electrolysis of water to gaseous hydrogen and oxygen:


 * 2H2O(I) &rarr; 2H2 + O2

Additional examples
An example of spontaneous decomposition is that of hydrogen peroxide, which will slowly decompose into water and oxygen:


 * 2H2O2 &rarr; 2H2O + O2

Carbonates 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 &rarr; H2O + CO2

Other carbonates will decompose when heated producing the corresponding metal oxide and carbon dioxide. In the following equation M represents a metal:


 * MCO3 &rarr; MO + CO2

A specific example of this involving calcium carbonate:


 * CaCO3 &rarr; CaO + CO2

Metal chlorates also decompose when heated. A metal chloride and oxygen gas are the products.


 * 2MClO3 &rarr; 2MCl + 3O2

A common decomposition of a chlorate to evolve oxygen utilizes potassium chlorate as follows:


 * 2KClO3 &rarr; 2KCl + 3O2

Many metal carbonates decompose to form metal oxides and carbon dioxide when heated.