Question

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

Answer 1

Decomposition reactions are those in which a compound breaks down to form two or more substances. These reactions require a source of energy to proceed. Thus, they are the exact opposite of combination reactions in which two or more substances combine to give a new substance with the release of energy.

Decomposition reaction: AB + Energy $→$ A + B
2H2O(l) $\xrightarrow{Electrolysis}$ 2H2(g) + O2(g)

Combination reaction: A + B $→$ AB + Energy
2H2(s) + O2(g) $→$ 2H2O(l) + Energy