What is the chemical equation for the thermal decomposition of calcium carbonate?

• A. CaCO3 -> CaO + CO2
• B. CaCO3 -> Ca + CO2
• C. CaCO3 -> CaO2 + CO2
• D. 2CaCO3 -> 2CaO + CO2

Answer: (A)

Thermal decomposition happens when heating causes a compound to break into simpler substances. For calcium carbonate, heating breaks it into calcium oxide (a solid) and carbon dioxide (a gas). The correct representation is CaCO3 -> CaO + CO2. It’s balanced: left has Ca1, C1, O3; right has CaO (Ca1, O1) and CO2 (C1, O2), totaling Ca1, C1, O3. This reflects one compound turning into two new substances with the same element counts.

Why the other ideas don’t fit: forming elemental calcium would require a reduction process, not just heating. A product like CaO2 isn’t a typical product of this reaction. And the alternative 2 CaCO3 -> 2 CaO + CO2 isn’t balanced for oxygen (left has six O, right has four O).