When malachite (Cu₂(CO₃)(OH)₂) reacts with hydrochloric acid (HCl), it releases carbon dioxide gas (CO₂) as one of the products. The reaction can be represented as follows:

Cu₂(CO₃)(OH)₂(s) + 4HCl(aq) → 2CuCl₂(aq) + CO₂(g) + H₂O(l)

In this reaction, malachite reacts with hydrochloric acid to produce copper chloride, carbon dioxide gas, and water. The carbon dioxide gas is released into the atmosphere as a product of the reaction.