When an acid reacts with metal carbonate, carbon dioxide gas is produced along with water and a salt:

Acid + Metal Carbonate → Salt + Water + Carbon Dioxide Gas

For example, when hydrochloric acid (HCl) reacts with sodium carbonate (Na₂CO₃), the reaction can be represented as follows:

2HCl + Na₂CO₃ → 2NaCl + H₂O + CO₂

In this reaction, sodium chloride (NaCl) is the salt formed, water (H₂O) is produced, and carbon dioxide (CO₂) gas is released.