What type of reaction is the following CaCO3 → CaO CO2

The reaction CaCO3 → CaO + CO2 is classified as a decomposition reaction (also called a thermal decomposition or breakdown reaction), where a single compound breaks apart into two or more simpler substances when heated. Calcium carbonate decomposes into calcium oxide (quicklime) and carbon dioxide gas when subjected to high temperatures, typically above 800-900°C in industrial kilns. This reaction follows the general decomposition pattern of AB → A + B, where one reactant yields multiple products.

This particular decomposition reaction is fundamental to the lime production industry and has been used for centuries in producing quicklime for construction, agriculture, and chemical manufacturing. The reaction is endothermic, meaning it requires continuous heat input to proceed—as soon as you stop heating, the reaction stops. This thermal decomposition of limestone (calcium carbonate) is one of the most economically important chemical reactions globally, as it's the primary method for producing lime, which has countless applications in cement production, steel manufacturing, water treatment, and soil pH adjustment. The reaction can be reversed under high pressure with CO2 to reform calcium carbonate, but under normal atmospheric conditions and high temperatures, the decomposition strongly favors the formation of CaO and CO2, with the carbon dioxide gas escaping into the atmosphere.