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10 Examples of Decomposition Reactions

A chemical reaction represents the conversion of reactants to product molecules. A chemical reaction can involve combination, synthesis, decomposition, or oxidation-reduction of reactant molecules. 
A decomposition reaction is also known as analysis reaction which is one of the most common chemical reactions out of all reactions. These reactions involve the decomposition or cleavage of reactant molecules to form small product molecules. 

The general decomposition reaction can be written as given below;
AB → A + B
For example; the electrolysis of water results the formation of oxygen and hydrogen gas involves the decomposition;
2 H2O → 2 H2 + O2
Similarly the decomposition of solid potassium chloride results the formation of solid potassium with gaseous chlorine molecule. 
The chemical reaction can be written as given below;
2 KCl(s) → 2 K(s) + Cl2(g)

Overall it is a type of chemical reaction which can be defined as the reaction which involves the splitting of a single compound into two or more simple substances under certain reaction conditions. 
We can consider it as the opposite reaction of the combination reaction. A combination reaction involves the combination of two or more simple substances to form a new bigger chemical substance. 
The digestion of food in human body is also an example of decomposition reaction in which the major constituent parts of food materials such as carbohydrates; fats etc. decompose to form simple compounds with a certain amount of energy. 
This energy is used in other metabolic activities of living bodies. Such types of reactions can be classified as thermal, electrolytic, and photo decomposition reaction. 
The thermal decomposition reaction is also known as thermolysis in which a single substance decomposes into 2 or more parts to form simple substance in the presence of heat. 

Such reactions are endothermic in nature as they require some heat to cleave the chemical bonds found in the chemical substance. 
For example; the decomposition of CaCO3 results the formation of CaO (calcium oxide) and CO2 (carbon dioxide) at high temperature. 
The reaction can be written as given below;
CaCO3(s) --> CaO(s) + CO2(g)
Similarly the decomposition of potassium chlorate (KClO3) at high temperature results the formation of solid potassium chloride and oxygen gas. Same reaction is used for the preparation of oxygen gas.

2KClO3(s) --> 2KCl (s) + 3O2(g)
This reaction can be carried out in the presence of catalyst MnO2 at low temperature. 
The decomposition of ferric hydroxide at high temperature results the formation of ferric oxide with water. 
Similarly the thermal decomposition of hydrated oxalic acid removes the water content from molecule to form anhydrous oxalic acid.

(COOH)2. 2H2O --> (COOH)2 + 2H2O
Another type of decomposition is electrolytic decomposition which is also known as electrolysis. 
This reaction takes place in presence of electric current in the aqueous solution of the sample. The electrolysis of water is the best example of electrolysis. 
The decomposition takes place by passing electric current through it. The reaction can be written as given below;
2H2O (l) --> 2H2(g) + O2(g)
Metallic salts such as sodium chloride can also electrolyzed to form molten sodium with chlorine gas on passing electricity in the molten sodium chloride. 
The photolysis or photo decomposition reaction involves the cleavage of given chemical compound in the presence of light.