Question

When calcium carbonate is heated, it gives calcium oxide and carbon dioxide. Is this reaction reversible or irreversible ?

Answer 1

This process is reversible.

At room temperature (around 298 K), calcium oxide will react with carbon dioxide (in the air, for example) to form calcium carbonate. Calcium oxide is used in absorption tubes to protect other chemicals from CO2 in the air. CaO(s) + CO2(g) → CaCO3(s) However, above about 1200 K the opposite reaction occurs, calcium carbonate decomposes to form calcium oxide and gives off carbon dioxide. This is what happens in lime kilns where limestone (calcium carbonate) is heated to form lime (calcium oxide). CaCO3(s) → CaO(s) + CO2(g) So it might make more sense to write CaCO3(s) =CaO(s) + CO2(g)