Dhristi JEE 2022-24

Definition of Decomposition

Decomposition can be defined as a process of breaking down or simplifying any physical or chemical entity. Chemical decomposition is sometimes also referred to as chemical breakdown. Chemical decomposition is the effect of simplifying a complex chemical entity into a single chemical entity into two or more fragments. Generally, it is the exact opposite of chemical synthesis. The breakdown of hydrogen peroxide to water and oxygen and the breakdown of water to hydrogen and oxygen are examples of chemical decompositions. In this article we are going to discuss the types of decomposition with examples in detail.


Decomposition Types

The decomposition is classified broadly into two types because changes can be of two types. There are two types of decomposition or we can say changes, which are given below.


  • Physical decomposition or changes

  • Chemical decomposition or changes


Physical changes are generally reversible changes but they can be also irreversible and only the physical properties are changed in such changes. In a physical change, a substance undergoes a change of its physical properties. Some common examples of physical changes are melting an ice cube, boiling of water, breaking of a glass, freezing water etc.


Chemical changes are irreversible changes in which new products are formed. The product is different from the reactants and has entirely different properties. Chemical changes that occur are also considered chemical reactions. A short way of writing a chemical reaction or the chemical changes are through chemical equations. Chemical equations are a symbolic representation of a chemical reaction. When one writes chemical reaction symbols of elements, arrows, etc are used.


Decomposition reaction - In this type of chemical reaction, one reactant breaks to form several products. It is just opposite to the combination reaction.


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Decomposition Meaning of Chemistry

Decomposition in chemistry means breaking a single reactant to form more stable products compared to the reactant. Decomposition is an essential process of chemistry as it results in the formation of new products. In our daily life, we see examples of chemical decomposition. For example when we open any soda bottle carbonic acid chemicals decompose into water and carbon dioxide, which creates the fizz.


Types of Decomposition Reactions

A decomposition reaction is classified into three types-

  • Thermal decomposition

  • Electrolytic decomposition

  • Photo decomposition


Now know about each type of decomposition reaction in detail.


  • Thermal Decomposition

It is a type of decomposition in which a single reactant is broken down into more than one product with the help of heat. Thermal energy or heat energy is used to break the reactants. This is an endothermic reaction as heat is used to break the bonds of the reactants. Calcium carbonate is decomposed from heat to form calcium oxide and carbon dioxide.


CaCO3→CaO + CO2


  • Photo Decomposition

It is a type of decomposition reaction in which light or photons are used to break the reactants to form several products. Light energy is used to break the bonds in the reactant. This reaction is also known as photolysis.


Silver chloride decomposes in the presence of sunlight to form silver metal and chlorine gas.


AgCl→Ag + Cl2


  • Electrolytic Decomposition

A single reactant is broken down into several products using electricity. This type of decomposition reaction is electrolytic decomposition. The decomposition of water is a good example of electrolytic decomposition.


H2O→ H2 + O2


Decomposition Reaction Examples

There are several examples of decomposition. Some of them are given below-

  • Carbonic acid in soft drinks decomposes to give carbon dioxide gas.

  • Hydrogen gas and oxygen gas are released from the decomposition of water.

  • Digestion of food is a decomposition reaction. Through this reaction, nutrients are released from the food eaten.

  • Iron sulphate which is of green colour is decomposed to form a brown-coloured ferric oxide and gases like sulphur dioxide and sulphur trioxide gases are released.

  • Lead nitrate on thermal decomposition gives lead monoxide which is yellow. With this brown gas nitrogen dioxide and oxygen gas are released.


Hence, decomposition is a process that results in a change that can be reversible or irreversible. It is an important process because many of the time decomposition is a need for the production or manufacture of any new product. In this article, we learnt about the type of decomposition and its examples as well.

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FAQs (Frequently Asked Questions)

1. Mention uses of decomposition reactions.

Decomposition reactions are used for various purposes. Some of them are given below. A decomposition reaction is used in the extraction of metals in different ways. Thermal decomposition is used to obtain mercury metal from its oxide (that is mercuric oxide)Thermal decomposition is used to obtain zinc oxide from its carbonate ore. 


ZnCO₃ →ZnO + CO₂


Electrolytic decomposition is used to obtain metal from its molten ores. Like sodium is obtained from its ore sodium chloride.


NaCl →Na + Cl₂


In the manufacture of cement, a decomposition reaction is used. The thermal decomposition of limestone is used to manufacture quick lime. The photodecomposition of silver bromide is used in photography.


AgBr → Ag + Br₂

2. Explain the characteristics of chemical reactions.

Chemical reactions are accompanied by certain features or signs. The important characteristics of chemical reactions are the evolution of gas, formation of precipitate, change in colour and change in temperature etc.

  • Evolution of gas: When metal like zinc reacts with an acid like sulphuric acid, hydrogen gas is evolved.

  • Formation of precipitate: The chemical reaction between lead nitrate and potassium iodide is accompanied by the formation of a yellow precipitate of lead iodide.

  • Change in colour: When iron reacts with copper sulphate (blue) a green colour is obtained due to the formation of iron oxide. Here colour change is seen.

  • Change in temperature: When quicklime reacts with water a lot of heat is released. This increases the temperature change.

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