The chemical reaction of calcium reacting with carbon dioxide can be represented in steps as follows:

Calcium (Ca) reacts with oxygen (O) to form calcium oxide (CaO):

2Ca + O2 → 2CaO

Calcium oxide (CaO) reacts with carbon dioxide (CO2) to form calcium carbonate (CaCO3):

CaO + CO2 → CaCO3

Calcium carbonate (CaCO3) reacts with carbonic acid (H2CO3) to form calcium bicarbonate (Ca(HCO3)2):

CaCO3 + H2CO3 → Ca(HCO3)2

Calcium bicarbonate (Ca(HCO3)2) decomposes into calcium carbonate (CaCO3) and carbon dioxide (CO2):

Ca(HCO3)2 → CaCO3 + CO2

Overall reaction:

2Ca + O2 + 2CO2 + 2H2O → 2CaCO3 + 2CO2

This demonstrates the pathway of calcium reacting with carbon dioxide to form calcium carbonate and carbon dioxide gas.