Why does copper metal deposit on zinc when zinc is placed in a copper(II) ion solution?

When zinc metal is placed in a solution containing copper(II) ions, a spontaneous oxidation-reduction reaction occurs, resulting in the deposition of copper metal.

This process is driven by the transfer of two electrons from the zinc to the copper. During this reaction:1

• Oxidation: The zinc metal acts as a reducing agent, losing two electrons to become an aqueous zinc ion ($Z{n}^{2+}$).1
• Reduction: The copper(II) ion ($C{u}^{2+}$) acts as an oxidizing agent, gaining those two electrons to be reduced into neutral copper metal.1

As the copper(II) ions are reduced and discharged as neutral atoms, they build into the metal lattice, effectively depositing copper onto the zinc surface. This reaction is thermodynamically spontaneous under standard conditions, with a potential of +1.10 volts. The overall process demonstrates the complementary nature of redox reactions, where the loss of electrons by one species is balanced by the gain of electrons by another.231