Question

How can a decomposition reaction be recognized?

Answer 1

Decomposition is a type of chemical reaction. It is defined as the reaction in which a single compound splits into two different or more simple compounds/substances under suitable conditions. It is also completely opposite to the combination reaction. There are three different types of decomposition reactions. So, they are Thermal decomposition reaction, Electrolytic decomposition reaction and Photo decomposition reaction.

Complete step-by-step answer: When a reaction has only one reactant, it is a decomposition reaction. In a decomposition reaction, a chemical reaction in which one reactant can yield two or more products.
It is represented as,
${\text{A }} \to {\text{ B}} + {\text{ C}}$
Example, the decomposition of water:
$2{H_2}O{\text{ }} \to {\text{ }}2{H_2} + {\text{ }}{O_2}$
There are three types of Decomposition Reactions;
Thermal decomposition reaction: It is also known as Thermolysis. When a chemical reaction is heated, the single reactant breaks into two or more simple substances, this reaction is known as thermal decomposition reaction. Generally, this reaction is endothermic, since heat is required to break the bonds present in the reactant.
Example, when the calcium carbonate (limestone) is heated, it gets decomposed to form calcium oxide (quick lime) and carbon dioxide. Quick lime is used for cement.
$CaC{O_3}(s)\,\,\xrightarrow{{Heat}}\,\,CaO(s)\,\, + \,\,C{O_2}(g)$
Electrolytic decomposition reaction: It is also known as Electrolysis. When electric current passed through an aqueous solution of a compound it gets decomposed.
Example, electrolysis of water.
$2{H_2}O(l){\text{ }}\xrightarrow{{Electric\,\,\,current}}{\text{ }}2{H_2}(g)\,\, + {\text{ }}{O_2}(g)$
Photo decomposition reaction: It is also known as Photolysis. When a substance is breaking down into a simpler substance by the exposure of light (photon) is called photolysis.
Example, when silver chloride is placed in a watch glass under sunlight for some time, the crystals slowly turns into a grey colour. It was found that the sunlight has caused decomposition of silver chloride into silver and chlorine.
$2AgCl(s)\,\,\xrightarrow{{Sunlight}}{\text{ }}2Ag(s)\, + {\text{ C}}{{\text{l}}_2}(g)$

Note: In a combination reaction, the substance gets combined and results in the formation of the chemical compound, while in a decomposition reaction, the substance breakdowns into two or more new substances.
Example: In the process of digestion of food, the number of decomposition reactions takes place. The major constituents of our food such as carbohydrates, proteins, fats, etc., breaks to form several simpler substances. These substances further react, releasing large amounts of energy in the form of ATP, that keeps our body working.