When an acid reacts with a carbonate, the three products are:

1. Salt: The acid's anion combines with the carbonate's cation to form a salt. For example, when hydrochloric acid (HCl) reacts with calcium carbonate (CaCO₃), the salt formed is calcium chloride (CaCl₂).

2. Carbon dioxide (CO₂): The carbonate ion (CO₃^2-) reacts with the hydrogen ions (H⁺) from the acid to form carbonic acid (H₂CO₃). Carbonic acid is unstable and readily decomposes into carbon dioxide and water.

3. Water (H₂O): This is a byproduct of the reaction, formed when the hydrogen ions from the acid react with the oxygen atoms in the carbonate ion.

Here is a general equation for the reaction:

Acid + Carbonate → Salt + Carbon dioxide + Water

Example:

HCl (aq) + CaCO₃ (s) → CaCl₂ (aq) + CO₂ (g) + H₂O (l)