Chemical decomposition, or chemical breakdown, is the process or effect of simplifying a single
chemical entity (normal molecule,
reaction intermediate, etc.) into two or more fragments. Chemical decomposition is usually regarded and defined as the exact opposite of
chemical synthesis
As a topic of chemistry, chemical synthesis (or combination) is the artificial execution of chemical reactions to obtain one or several products. This occurs by physical and chemical manipulations usually involving one or more reactions. In moder ...
. 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 but some of the process is understood; much energy is needed to break bonds. Since all decomposition reactions break apart the bonds holding it together in order to produce into its simpler basic parts, the reactions would require some form of this energy in varying degrees. Because of this fundamental rule, it is known that most of these reactions are endothermic although exceptions do exist.
The stability of a chemical compound is eventually limited when exposed to extreme environmental conditions such as
heat
In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...
,
radiation
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:
* ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...
,
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, dew, or fog to be present.
Humidity dep ...
, or the
acidity
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a ...
of a
solvent
A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
. Because of this chemical decomposition is often an undesired
chemical reaction
A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...
. However chemical decomposition is being used in a growing number of ways.
For example this method is employed for several analytical techniques, notably
mass spectrometry, traditional
gravimetric analysis
Gravimetric analysis describes a set of methods used in analytical chemistry for the quantitative determination of an analyte (the ion being analyzed) based on its mass. The principle of this type of analysis is that once an ion's mass has been ...
, and
thermogravimetric analysis
Thermogravimetric analysis or thermal gravimetric analysis (TGA) is a method of thermal analysis in which the mass of a sample is measured over time as the temperature changes. This measurement provides information about physical phenomena, such ...
. 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
An example is the
electrolysis of
water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
to the gases
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
and
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
:
: 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 viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3% ...
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 (H2CO3), 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 g ...
s will decompose. A notable exception is
carbonic acid, (H
2CO
3). Commonly seen as the "fizz" in carbonated beverages, carbonic acid will spontaneously decompose over time into
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
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 (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
oxide 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:
: CaCO
3 → CaO + CO
2
Metal
chlorates also decompose when heated. In this type of decomposition reaction, a metal
chloride
The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts ...
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 chemistry studies and uses instruments and methods to separate, identify, and quantify matter. In practice, separation, identification or quantification may constitute the entire analysis or be combined with another method. Separati ...
*
Thermal 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 re ...
References
External links
{{commonscat
* https://quizlet.com/42968634/types-of-decomposition-reactions-flash-cards/ PDF
Biodegradation database
Inorganic chemistry
Organic chemistry
Chemical reactions