The acid-base chemical reaction that is irreversible is when a strong acid is added to water. In this reaction, the strong acid completely dissociates in water, releasing a high concentration of hydrogen ions (H⁺), which leads to a significant change in the pH of the solution. The dissociation does not revert back to the original form of the acid, making it effectively irreversible under normal conditions.
In contrast, when weak acids or weak bases are added to water, they only partially dissociate, and the reaction can reach an equilibrium state, making those processes reversible. Water on its own does not involve any acid-base reaction, so it cannot be classified as irreversible.