What property of calcium oxide means it reacts readily with carbon dioxide?
Calcium oxide, like many other metal oxides, forms a chemical bond with CO2 to form a carbonate. Thermodynamically, the reaction between CaO and CO2 to form CaCO3 is accompanied (at room temperature) by a decrease in the free energy of the system. If the CaO (called lime) is porous, the CO2 will diffuse throughout the piece and eventually, at room temperature, convert it completely to CaCO3 (called limestone). The reaction to form limestone is so favorable that lime will react with the CO2 in the atmosphere. What’s more, if the lime has already reacted with water vapor to form hydrated lime (CaH2O2), the hydrated lime will also react with CO2 from the atmosphere to form limestone. If you heat limestone to 1200 degrees Celsius, it will decompose back to lime and CO2.
