How does corrosion of zinc in acid involve both metal dissolution and hydrogen gas formation?

When zinc is immersed in an acid solution, it establishes a corrosion couple, which is a system where two distinct electrochemical reactions occur simultaneously on the metal surface.1

The process involves two complementary reactions:

• Metal Dissolution (Oxidation): The zinc metal tends to establish a potential that causes it to eject metal ions into the solution. In this anodic process, zinc is oxidized to form zinc ions (${\text{Zn}}^{2+}$).1
• Hydrogen Gas Formation (Reduction): Simultaneously, the potential of the zinc is sufficiently negative to facilitate the reduction of hydrogen ions present in the acidic solution. These ions accept electrons to form hydrogen gas, a cathodic process that results in hydrogen evolution.1

Because these two processes occur at comparable rates on the same metal, a spontaneous corrosion cycle is established. The overall rate of this reaction is determined by the mixed potential of the metal, which is reached when the rates of the anodic dissolution and cathodic reduction are balanced.1