Which compound is produced when carbon dioxide reacts with water to form H₂CO₃?

The compound produced when carbon dioxide reacts with water to form H₂CO₃ is carbonic acid.

Carbonic acid forms when dissolved carbon dioxide reacts reversibly with water: CO₂ + H₂O ⇌ H₂CO₃. It is a weak acid, meaning that only a fraction of its molecules release hydrogen ions in water. The equilibrium between carbon dioxide, carbonic acid, bicarbonate, and carbonate is central to natural water chemistry.

Carbonic acid helps give carbonated drinks their tangy taste and contributes to the weathering of carbonate rocks. In oceans, the same chemistry links atmospheric carbon dioxide with seawater acidity. Increased dissolved carbon dioxide shifts the system toward more hydrogen ions, a process associated with ocean acidification.

Carbonic acid should not be confused with carbon dioxide itself. Carbon dioxide is a gas, while carbonic acid is the hydrated form present in aqueous equilibrium. In pure form, carbonic acid is difficult to isolate because it readily breaks down again.