Which statement describes a decomposition reaction?

Which statement describes a decomposition reaction?

• A. A compound breaks into two or more simpler substances
• B. Two elements combine to form a compound
• C. A compound and element exchange parts
• D. A substance changes into energy only

Answer: (A)

Decomposition reactions involve a single compound breaking apart into two or more simpler substances. This is the reverse of synthesis, and the bonds in the compound are broken to yield simpler products, often with energy input such as heat or electricity. A classic example is heating calcium carbonate to produce calcium oxide and carbon dioxide: CaCO3 → CaO + CO2. The other scenarios describe different reaction types: forming a compound from two elements is synthesis; exchanging parts between a compound and an element is a displacement reaction; and turning a substance into energy only isn’t a typical chemical decomposition (it points to processes beyond standard chemical reactions).

Decomposition reactions involve a single compound breaking apart into two or more simpler substances. This is the reverse of synthesis, and the bonds in the compound are broken to yield simpler products, often with energy input such as heat or electricity. A classic example is heating calcium carbonate to produce calcium oxide and carbon dioxide: CaCO3 → CaO + CO2. The other scenarios describe different reaction types: forming a compound from two elements is synthesis; exchanging parts between a compound and an element is a displacement reaction; and turning a substance into energy only isn’t a typical chemical decomposition (it points to processes beyond standard chemical reactions).