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Examples of Decomposition Reaction

A chemical reaction involves the conversion of some chemical substances to new ones with the formation and cleavage of chemical bonds between atoms. There are various types of chemical reactions which depend upon the reactants, reaction conditions and other factors. Let’s have a look on certain type of chemical reaction which is known as decomposition reaction. In a decomposition reaction, one chemical substance decomposes into two or more chemical substances under suitable reaction conditions.

We can consider the decomposition reaction as the reverse process of synthesis or combination process. Remember a combination reaction involves the formation of a new chemical substance from the combination of two or more chemical substances. Let’s discuss some common examples of decomposition reaction.  Digestion of food in human body is an example of decomposition reaction. In digestion reaction, major constituents of our food like fats, proteins and carbohydrates decompose to form many simple substances. 

The decomposition of thee Biomolecules releases a large amount of energy which provides energy to our body. The general chemical equation for the decomposition reaction can be written as given below;

AB A + B

There are several decomposition reactions in our surroundings. For example, electrolysis of water results the formation of oxygen and hydrogen gas. The chemical equation can be written as;

2 H2O → 2 H2 + O2

Similarly the decomposition of potassium chloride forms solid potassium and gaseous chlorine.

2 KCl(s) → 2 K(s) + Cl2(g)

On the basis of reaction conditions, the decomposition reactions can be classified in different types such as thermal decomposition, electrolytic decomposition and photo decomposition reaction. Thermal decomposition reaction or thermolysis involves the cleavage of one chemical substance into two or more simple substances in the presence of heat. These reactions are endothermic reactions as they require some heat to cleave the chemical bonds.
For example the calcium carbonate or lime stone forms calcium oxide and carbon dioxide in the presence of heat. This reaction is used in the manufacturing of cement.

CaCO3(s) + heat  CaO(s)  + CO2(g)

Similarly the decomposition of potassium chlorate also occurs in the presence of heat and form potassium chloride and oxygen. This is one of the preparation methods of oxygen in the laboratory.

2KClO3(s) + heat  2KCl(s)  + 3O2(g)

Sam reaction can be continued in the presence of manganese dioxide (MnO2) as catalyst.
The decomposition of ferric hydroxide and hydrated oxalic acid is also an example of thermal decomposition. The decomposition of ferric hydroxide forms ferric oxide and water whereas the decomposition of hydrate oxalic acid forms oxalic acid with water.

2Fe(OH)3 + heat → Fe2O3 + 3H2O
 H2C2O4 .2H2 H2C2O4 + 2H2O

Another type of decomposition is electrolytic decomposition reaction which is also named as electrolysis. Such reactions occur in the presence of electricity in the aqueous solution.

For example electrolysis of water occurs in the presence of electricity to form hydrogen and oxygen gas whereas the electrolysis of sodium chloride forms molten sodium metal with chlorine gas.

2H2O(l) → 2H2(g)  + O2(g)
2NaCl (l) → 2Na (l) + Cl2(g)

Decomposition reactions can also occur in the presence of light and known as photo decomposition reaction or photolysis. For example silver chloride decomposes to form solid silver with chlorine gas.

2AgCl (s)  + Sunlight → 2Ag (s)  + Cl2 (g)