Question

Explain different types of decomposition reaction

Answer 1

Decomposition reaction

1. A decomposition reaction can be defined as a chemical reaction in which one reactant breaks down into two or more products.
2. General representation of the reaction

$AB\to A+B$

Where AB is the reactant and A and B are the product molecules.

Example: Decomposition of carbonic acid

$\underset{\mathrm{Carbonic}\mathrm{acid}}{{\mathrm{H}}_2{\mathrm{CO}}_3\left(\mathrm{l}\right)}\to \underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}+\underset{\mathrm{Carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}$

Types of decomposition reaction

The three primary types of decomposition reactions are:

Thermal decomposition reaction:

• A thermal decomposition reaction can be defined as a decomposition reaction that is initiated by thermal energy.
• The thermal decomposition reaction needs the energy to be supplied to the reactants in the form of heat.
• These reactions are generally endothermic reactions, as energy is required to break the chemical bonds and separate the constituent elements
• An example of a thermal decomposition reaction is the decomposition of Calcium carbonate.

$\underset{\mathrm{Calcium}\mathrm{carbonate}}{{\mathrm{CaCO}}_3\left(\mathrm{s}\right)}\stackrel{\mathrm{heat}}{\to }\underset{\mathrm{Calcium}\mathrm{oxide}}{\mathrm{CaO}\left(\mathrm{s}\right)}+\underset{\mathrm{carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}$

• On heating, calcium carbonate decomposes into calcium oxide and carbon dioxide.
• This process is used in the manufacturing of quick lime, which is an important substance in many industries.

Electrolytic decomposition reaction:

• An electrolytic decomposition reaction is a type of decomposition reaction in which the activation energy for decomposition is provided in the form of electrical energy.
• An example of an electrolytic decomposition reaction is the electrolysis of water, which can be represented by the given chemical equation:

$\underset{\mathrm{Water}}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Hydrogen}}{2{\mathrm{H}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Oxygen}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}$

• Acidified water on electrolysis gives hydrogen gas and oxygen gas.

Photo decomposition/ photolytic decomposition/ photochemical decomposition:

• A photodecomposition reaction is a type of decomposition reaction in which the reactant is broken down to its constituents by absorbing energy from photons.
• An example of a photodecomposition reaction is:

$\underset{\mathrm{Ozone}}{{\mathrm{O}}_3}\stackrel{\mathrm{h\nu }}{\to }\underset{\mathrm{Oxygen}}{{\mathrm{O}}_2}+\underset{\mathrm{Oxygen}\mathrm{free}\mathrm{radical}}{{\mathrm{O}}^{.}}$

• Ozone in the photochemical condition undergoes decomposition to give oxygen gas and oxygen-free radical.

There are 3 different types of decomposition reactions thermal, electrolytic, and photolytic.