Decomposition Reaction

Decomposition Reaction

What is a decomposition reaction

A decomposition reaction can be defined as a type of chemical reaction in which under suitable conditions, one single compound splits into multiple simpler substances.

General Reaction mechanism

AB -> A + B

Decomposition Reaction

Decomposition reaction examples

Decomposition reaction happens all throughout, but we often cease to see it. Let us look at some decomposition reaction examples in real life.

  • KClO3 decomposition reaction
  • H2O2 decomposition reaction

Even Though the decomposition reaction concept is simple, these are some of the common doubts people have about the concept.

Why are decomposition reaction called the opposite of combination reaction?

We know a combination reaction to be a chemical reaction in two or more substances combine together to produce a new compound. Whereas in a decomposition reaction, the combination between constituents are broken down to form multiple products.

Are all decomposition reactions endothermic?

No, not all decomposition reactions are endothermic. A decomposition reaction can be both endothermic or exothermic, even though the latter is more predominant


  • Decomposition of NO to N2 & O2 is exothermic.
  • Decomposition of ozone (O3) to oxygen (O2) is exothermic.

State an important use of decomposition reaction?

One major application of the decomposition is the extraction of metals from its ore. Like obtaining zinc from calamine and Sodium from sodium from sodium chloride.

Double decomposition reaction

A double decomposition reaction is a type of decomposition reaction in which two constituent reactants interchange positive and negative ions and form two new compounds.

Decomposition Reaction


HCl(aq) + NaOH(aq) → NaCl(aq) + HOH(l)

Types of decomposition reaction

Let us look at the three main types of decomposition reactions which we see around us.

    • Thermal decomposition reaction A thermal decomposition reaction can be defined as a decomposition reaction which is activated by thermal energy. The reaction is generally endothermic as energy is required to break chemical bond in order to separate the constituent elements.
      • example of thermal decomposition reaction
        • CaCO3 → CaO + CO2 When heated Calcium Carbonate,decomposes into Calcium Oxide and Carbon Dioxide. This process is employed in the manufacturing of quick lime which is an important component in industries.
  • Electrolytic decomposition reaction
      • An electrolytic decomposition reaction is a type of decomposition reaction in which the activation energy for decomposition. Example of electrolytic decomposition reaction
        • Dissociation of water:2H2O→ 2H2 + O2
  • Photo decomposition/ photolytic decomposition/ photochemical decomposition
    • A photo decomposition is the type of decomposition reaction in which the reactant is broken down to its constituents by photons.Example of photo decomposition reaction
      • O3 + hν → O2 + O(1D)Photolysis occurs in the atmosphere wherein ozone molecules is broken down into oxygen molecule and atomic oxygen.

Uses of decomposition reaction

  • Manufacture of cement or calcium oxide
  • For metallurgical processes: Extraction of metals from its oxides,chloride etc
  • The relief from acid indigestion
  • Thermite welding

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Practise This Question

In the nitration of benzene with a mixture of conc HNO3 and conc H2SO4, the active species involved are