Question: Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Answer: 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) + Electrolysis ⟶ 2H₂(g) + O₂(g)
Combination Reaction: A + B ⟶ AB + Energy
2H₂(g) + O₂(g) ⟶ 2H₂O(l) + Energy
