Decomposition Reaction

Last Updated : 07 Feb, 2024

Have you ever wondered what happens when compounds break apart into simpler substances? Or how energy is released, and new compounds are formed? The answers to these questions lie in the concept of Decomposition Reaction. Decomposition Reactions are a key concept in the understanding of the chemical breakdown of a complex substance. In this article we will learn about this reaction in detail, also we will learn various examples and their types as well. So, let’s start the article by answering the question “What is a Decomposition Reaction?”.

Decomposition Reaction Definition

We can define a Decomposition Reaction as a chemical process in which the molecule or reactant breaks down into simpler products.

It is just the opposite of the combination reaction and the energy required for breaking down of product can be in the form of heat, light, or electricity.

For example, by heating calcium carbonate it breaks down into calcium oxide and carbon dioxide gas. The balanced reaction of this can be written as follows:

[Tex]\bold{\text{CaCO}_3(s) \xrightarrow{\Delta} \text{CaO (s)} + \text{CO}_2 ~\text{(g)}} [/Tex]

General Equation of Decomposition Reaction

For any compound AB, the general equation of the decomposition reaction can be given as:

AB → A + B

In the above reaction, AB represents the reactant which is a chemical compound of A and B that starts the reaction, while A and B represent the products obtained by the reaction. and the arrow represents the direction in which the reaction occurs.

Decomposition Reaction Examples

Here are some important examples of Decomposition Reactions:

Electrolysis of Water

The electrolysis process is an excellent example of a decomposition reaction. The reaction takes place by breaking down molecules by passing electricity.

H₂O (l) ⇢ 2H₂(g)+ O₂ (g)

Decomposition Reaction of Hydrogen Peroxide

Hydrogen peroxide breaks down into water and oxygen in the presence of light, as shown below:

Decomposition Reaction of KClO₃

The decomposition reaction of potassium chlorate (KClO₃) can be represented by the following balanced chemical equation:

2KClO₃(s) → 2KCl(s) + 3O₂(g)

In this reaction, solid potassium chlorate (KClO₃) decomposes into solid potassium chloride (KCl) and oxygen (O₂). The reaction is typically initiated by potassium chlorate, which provides the energy required for the decomposition to occur.

Decomposition Reaction of Metal Carbonates

When metal carbonates are heated, it gets decomposed into their metal oxides and carbon dioxide. For Example, Calcium carbonate get decomposed to Calcium oxide and Carbon Dioxide while, Sodium Carbonate get decomposed to Sodium oxide and Carbon Dioxide, as shown below:

Decomposition Reaction of Metal Hydroxides

On heating, metal hydroxides break down into metal oxides and water. Thus, Water and sodium oxide is produced during the breakdown of sodium hydroxide, as shown below:

Decomposition Reaction of Oxy Acids

The decomposition of oxy acids leads to the production of carbon dioxide and water as shown below:

Types of Decomposition Reaction

The decomposition reactions are majorly classified into three types:

Thermal Decomposition Reaction
Electrolytic Decomposition Reaction
Photo Decomposition Reaction

Thermal Decomposition Reaction

A single substance can split into two or more simple substances when heated in a chemical process known as thermal decomposition or Thermolysis. Since heat is necessary to break the substance’s bonds, the reaction is usually endothermic.

For example, when potassium chlorate is heated it decomposed into potassium chloride and oxygen i.e.,

Thermal Decomposition of potassium chlorate

Electrolytic Decomposition Reaction

When an electric current is passed through an aqueous solution of a substance, electrolytic decomposition may occur. It is also called Electrolysis.

Water electrolysis works as a good example of an Electrolytic Decomposition Reaction.

Photo Decomposition Reaction

Photo decomposition is a chemical reaction in which a chemical compound is split up into simple substances by exposure to light (photons).

For example, when a small amount of silver chloride (AgCl) is taken in a watch glass and exposed to the sun for a while. The crystals gradually start to turn grey. Analysis reveals that silver chloride has broken down into silver and chlorine due to sunshine as shown below:

Double Decomposition Reaction

A double decomposition reaction is a reaction between two compounds in which components of each substance are exchanged out to create two new compounds.

One or more of the reactants in a double decomposition reaction is insoluble in the solvent in this type of reaction.

In these reactions, the positive ion of one molecule is exchanged for the positive ion of the other component.

For example, zinc chloride and hydrogen sulphide gas are produced when zinc sulphide and hydrochloric acid react. There, zinc sulphide is both solid and undissolved in an aqueous medium.

Uses of Decomposition Reactions

Various uses of the Decomposition reaction are,

Decomposition reactions are widely used to extract the metal.
Decomposition reactions help to manufacture cement or calcium oxide.
The decomposition reaction cause the fizz in a soda bottle.
This reaction is very helpful to break down hazardous waste.
Also, it is important for the human digestive system to digest food.

Difference between Combination and Decomposition Reaction

These are some of the key differences between both combination and decomposition reactions :

Combination Reaction vs. Decomposition Reaction
Property	Combination Reaction	Decomposition Reaction
Definition	A reaction where two or more substances combine to form a single product.	A reaction where a single compound breaks down into two or more simpler substances.
Reactants	Two or more elements or compounds.	A single compound.
Products	A single compound.	Two or more elements or compounds.
Energy Change	Often release energy in the form of heat or light.	Often require an external energy source (such as heat) to initiate the reaction.
Example	2Mg + O₂ → 2MgO	2H₂O₂ → 2H₂O + O₂

Also, Read :

FAQs on Decomposition Reaction

What is Decomposition Reaction?

Decomposition reactions as the name suggests are the reaction in which a complex compound breaks down into smaller and simpler compounds. For example, we can consider the electrolysis of water i.e.,

H₂O (l) ⇢ 2H₂(g)+ O₂ (g)

Write 5 Examples of Decomposition Reactions.

Five examples of decomposition reactions are:

Electrolysis of water.
Decomposition of Hydrogen peroxide into water and oxygen.
Decomposition of carbonic acid into water and carbon dioxide.
Decomposition of Potassium of Chlorate into potassium chloride and oxygen.
Decomposition of sodium hydroxide into sodium oxide and water.
All these reactions are discussed in the article above.

What are Types of Decomposition Reactions?

There are different types of decomposition reactions based on the type of energy given to the compound,

Thermal Decomposition Reaction
Electrolytic Decomposition Reaction
Photo Decomposition Reaction

What is Electrolytic Decomposition Reaction?

When an electric electric current is passed through an aqueous solution of a substance, electrolytic decomposition may occur. Water electrolysis works as a good example for Electrolytic Decomposition Reaction.

What is Double Decomposition Reaction?

A double replacement reaction is a reaction between two compounds in which the positive ion of one molecule is exchanged for the positive ion of the other component. For example, zinc chloride and hydrogen sulphide gas are produced when zinc sulphide and hydrochloric acid react.

What is Thermal Decomposition Reaction?

When a single substance split into two or more simple substances when heated in a chemical process known as thermal decomposition. Since heat is necessary to break the substance’s bonds, the reaction is usually endothermic.

Is Decomposition Reactions Exothermic or Endothermic?

Yes, almost all decomposition reactions required heat to breakdown, therefore are endothermic in nature.

What is Difference Between Combination and Decomposition Reaction?

The major difference between Combination and Decomposition Reaction is that in a combination reaction, the reactants combine to form the product. However, in a decomposition reaction, one reactant can form two or more products by the breakage of bonds.

What is the Decomposition Reaction of Ferrous Sulphate?

Upon heating, ferrous sulphate decomposes into ferric oxide (Fe₂O₃), sulfur dioxide (SO₂), and sulfur trioxide (SO₃). The reaction can be represented as:

2FeSO₄→ Fe2O₃ + SO₂ + SO₃

What is the Decomposition Reaction of Copper Sulphate?

The decomposition reaction of copper sulphate (CuSO₄) involves heating, where it breaks down into copper(II) oxide (CuO), sulfur dioxide (SO₂), and oxygen (O₂). The reaction can be summarized as:

2CuSO₄→2CuO+ 2SO₂ +O₂

What is the Decomposition Reaction of Lead Nitrate?

The decomposition reaction of lead nitrate (Pb(NO₃)₂) occurs upon heating, resulting in lead(II) oxide (PbO), nitrogen dioxide (NO₂), and oxygen (O₂). The equation representing this reaction is:

2Pb(NO₃)₂→ 2PbO + 4NO₂+ O₂

Effects of Oxidation Reactions in Everyday Life

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