In a reaction where solid calcium carbonate is heated to release CO2 and CaO, what is the type of reaction and the products?

• A. Synthesis; CaO and CO2
• B. Thermal decomposition; CaO and CO2
• C. Combustion; CaCO3 + heat -> CaO + CO2
• D. Acid-base reaction; CaCO3 + HCl -> CaCl2 + CO2 + H2O

Answer: (A)

The concept here is a decomposition reaction driven by heat. When calcium carbonate is heated, it breaks apart into calcium oxide and carbon dioxide: CaCO3(s) → CaO(s) + CO2(g). This is not forming a new compound from simpler parts (synthesis); instead, one compound splits into two products. The products are a solid calcium oxide and a gaseous carbon dioxide. This kind of thermal decomposition of carbonates is common in processes like lime production.