No, CaCO3(s) → CaO(s) + CO2(g) is an endothermic reaction.
This is the decomposition of limestone to calcium oxide (quicklime) and carbon dioxide on heating.
A decomposition reaction is a chemical reaction in which a single compound breaks down into two or more elements or new compounds. Hence, it is an example of a decomposition reaction.
- Increasing the temperature favours the decomposition of calcium carbonate. The forward reaction is endothermic and absorbs heat – the system is trying to minimise the temperature increase.
- Decreasing the temperature favours the formation of calcium carbonate. The backward reaction is exothermic, so more heat is released – the system is trying to minimise the temperature decrease.