Question

Why are decomposition reactions called the opposite of combination reactions? Write equations for decomposition reactions.

[3 Marks]

Answer 1

Combination reaction is said to be the reaction between two or more molecules to form a larger molecule; whereas the decomposition reaction is defined as the splitting of larger molecules into two or more smaller molecules. This essentially explains that the decomposition reaction is the opposite of the combination reaction.

[2 Marks]

Few examples of decomposition reactions are:

• $ZnC{O}_3\left(s\right)\to ZnO\left(s\right)+C{O}_2\left(g\right)$
• $CaC{O}_3\left(s\right)\to CaO\left(s\right)+C{O}_2\left(g\right)$
• $2HgO\left(s\right)\to 2Hg\left(s\right)+O_2\left(g\right)$

[1 Mark]