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) \(\xrightarrow{Electrolysis}\)  2H_2(g) + O_2(g)

Combination reaction: A + B \(→\) AB + Energy
2H_2(s) + O_2(g) \(→\) 2H₂O_(l) + Energy