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

The decomposition reaction is defined as the splitting of bigger molecules into two or smaller molecules, whereas the combination reaction is considered to be the reaction of two or more molecules to generate a larger molecule. Essentially, this describes how the decomposition process is the combination reaction\’s polar opposite.

Since the heat from the surrounding or generated heat is required to break the bonds of the bigger molecule, the breakdown reaction is typically endothermic. Several examples of breakdown reactions include

ZnCO₃ + Heat → ZnO + CO₂

CaCO₃ + Heat → CaO + CO₂

2HgO → 2Hg + O₂