
Chemical decomposition, or chemical breakdown, is the process or effect of simplifying a single
chemical entity (normal molecule,
reaction intermediate
In chemistry, a reaction intermediate, or intermediate, is a molecular entity arising within the sequence of a stepwise chemical reaction. It is formed as the reaction product of an elementary step, from the reactants and/or preceding interme ...
, etc.) into two or more fragments. Chemical decomposition is usually regarded and defined as the exact opposite of
chemical synthesis. In short, the chemical reaction in which two or more products are formed from a single reactant is called a decomposition reaction.
The details of a decomposition process are not always well defined. Nevertheless, some activation energy is generally needed to break the involved bonds and as such, higher temperatures generally accelerates decomposition. The net reaction can be an
endothermic process, or in the case of spontaneous decompositions, an
exothermic process.
The stability of a chemical compound is eventually limited when exposed to extreme environmental conditions such as
heat
In thermodynamics, heat is energy in transfer between a thermodynamic system and its surroundings by such mechanisms as thermal conduction, electromagnetic radiation, and friction, which are microscopic in nature, involving sub-atomic, ato ...
,
radiation
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or a material medium. This includes:
* ''electromagnetic radiation'' consisting of photons, such as radio waves, microwaves, infr ...
,
humidity
Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation (meteorology), precipitation, dew, or fog t ...
, or the
acidity of a
solvent
A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...
. Because of this chemical decomposition is often an undesired
chemical reaction
A chemical reaction is a process that leads to the chemistry, chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an Gibbs free energy, ...
. However chemical decomposition can be desired, such as in various waste treatment processes.
For example, this method is employed for several analytical techniques, notably
mass spectrometry
Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a ''mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is used ...
, traditional
gravimetric analysis, and
thermogravimetric analysis. Additionally decomposition reactions are used today for a number of other reasons in the production of a wide variety of products. One of these is the explosive breakdown reaction of
sodium azide 3)2">NaN3)2into nitrogen gas (N
2) and sodium (Na). It is this process which powers the life-saving airbags present in virtually all of today's automobiles.
Decomposition reactions can be generally classed into three categories; thermal, electrolytic, and photolytic decomposition reactions.
Reaction formula
In the breakdown of a compound into its constituent parts, the generalized reaction for chemical decomposition is:
: AB → A + B (AB represents the reactant that begins the reaction, and A and B represent the products of the reaction)
An example is the
electrolysis
In chemistry and manufacturing, electrolysis is a technique that uses Direct current, direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of c ...
of
water
Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...
to the gases
hydrogen
Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
and
oxygen
Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
:
: 2 H
2O() → 2 H
2() + O
2()
Additional examples
An example of a spontaneous (''without'' addition of an external energy source) decomposition is that of
hydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...
which slowly decomposes into water and oxygen
(see video at right):
: 2 H
2O
2 → 2 H
2O + O
2
This reaction is one of the exceptions to the endothermic nature of decomposition reactions.
Other reactions involving decomposition do require the input of external energy. This energy can be in the form of heat, radiation, electricity, or light. The latter being the reason some chemical compounds, such as many prescription medicines, are kept and stored in dark bottles which reduce or eliminate the possibility of light reaching them and initiating decomposition.
When heated,
carbonate
A carbonate is a salt of carbonic acid, (), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word "carbonate" may also refer to a carbonate ester, an organic compound containing the carbonate group ...
s will decompose. A notable exception is
carbonic acid
Carbonic acid is a chemical compound with the chemical formula . The molecule rapidly converts to water and carbon dioxide in the presence of water. However, in the absence of water, it is quite stable at room temperature. The interconversion ...
, (H
2CO
3). Commonly seen as the "fizz" in carbonated beverages, carbonic acid will spontaneously decompose over time into
carbon dioxide
Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
and water. The reaction is written as:
: H
2CO
3 → H
2O + CO
2
Other carbonates will decompose when heated to produce their corresponding
metal
A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, electricity and thermal conductivity, heat relatively well. These properties are all associated wit ...
oxide
An oxide () is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of −2) of oxygen, an O2− ion with oxygen in the oxidation st ...
and carbon dioxide.
The following equation is an example, where ''M'' represents the given metal:
: ''M''CO
3 → ''M''O + CO
2
A specific example is that involving
calcium carbonate
Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...
:
: CaCO
3 → CaO + CO
2
Metal
chlorates also decompose when heated. In this type of decomposition reaction, a metal
chloride
The term chloride refers to a compound or molecule that contains either a chlorine anion (), which is a negatively charged chlorine atom, or a non-charged chlorine atom covalently bonded to the rest of the molecule by a single bond (). The pr ...
and oxygen gas are the products. Here, again, ''M'' represents the metal:
: 2 ''M''ClO
3 → 2 ''M''Cl+ 3 O
2
A common decomposition of a chlorate is in the reaction of
potassium chlorate where oxygen is the product. This can be written as:
: 2 KClO
3 → 2 KCl + 3 O
2
See also
*
Analytical chemistry
Analytical skill, Analytical chemistry studies and uses instruments and methods to Separation process, separate, identify, and Quantification (science), quantify matter. In practice, separation, identification or quantification may constitute t ...
*
Thermal decomposition
References
External links
* https://quizlet.com/42968634/types-of-decomposition-reactions-flash-cards/ PDF
Biodegradation database
{{Authority control
Inorganic chemistry
Organic chemistry
Chemical reactions