How Are Combination and Decomposition Reactions Related?

We will discuss how are combination and decomposition reactions related to each other. We have already discussed combination and decomposition reactions. They are opposite to each other.

Actually, we will discuss the difference between combination and decomposition reactions with examples.

What is a combination reaction?

The chemical reactions in which two or more reactants combine to form a single product are called combination reactions.

     A   +   B   → AB

What is a decomposition reaction?

The chemical reactions in which a reactant(substance) breaks down into two or more products are called decomposition reactions.

    AB   →  A   +   B  

Example of combination reaction

Following are the examples of combination reaction

i). Burning of coal

`C  +   O_2  →  CO_2`

ii). Hydrogenation of ethane

 `CH_2= CH_2 + H_2 →  CH_3=CH_3`

iii). Formation of ammonia

`N_2  + 3H_2   → 2NH_3`

iv). Formation of magnesium oxide

`Mg+   O_2  → 2MgO`

v). Formation of water

`H_2 + O_2 →  2H_2O`

Example of decomposition reaction

Following are the examples of decomposition reaction

i). Electrolysis of water

  `2H_2O\overset\text{electric current}{\rightarrow} 2H_2 + O_2`

ii). Decomposition of calcium carbonate

 `CaCO_3\overset{\Delta }{\rightarrow}CaO + O_2`

iii). Photolysis of HBr

  `2HBr\overset{sun light}{\rightarrow} H_2+ Br_2`

iv). Decomposition of sodium chloride

`2NaCl\overset\text{electric current}{\rightarrow} 2Na  + Cl_2`

v). Decomposition of KClO3

   `2KClO_3\overset{heat}{\rightarrow}2KCl+ 3O_2` 

So combination and decomposition reactions are opposite reactions.

Relationship between Combination and Decomposition Reactions

Although combination and decomposition reactions are opposite chemical reactions, they seem closely related in the reverse nature of these reactions. The product of a combination reaction can serve as the reactant in a decomposition reaction, and vice versa.

`N_2+3H_2 ⇌2NH_3` 

In the above reaction, nitrogen and hydrogen combine to form ammonia (forward reaction), this is combination reaction.

In the backward reaction, ammonia breaks down into nitrogen and hydrogen, this is a decomposition reaction.

 Conclusion

Combination reactions involve the formation of complex substances and decomposition reactions involve the formation of simple substances.

Related Topics

1. What happens during a chemical reaction