How can changes in zinc(II) and copper(II) ion concentrations affect the direction of their redox reaction?

The direction of the redox reaction between zinc and copper(II) ions is influenced by their concentrations, as described by the Nernst equation. Under standard conditions, where both zinc(II) ion (Zn²⁺) and copper(II) ion (Cu²⁺) are at a concentration of 1 mole per liter (1M), the reaction proceeds spontaneously with a potential of +1.10 volts.1

If the ratio of zinc(II) ion concentration to copper(II) ion concentration increases, the reduction potential (E) decreases. If this ratio becomes very high, the potential can reach 0 volts, indicating a state of chemical equilibrium where there is no net tendency for the reaction to proceed in either direction. If the ratio were to increase further, the spontaneity would reverse, favoring the oxidation of copper metal by zinc ions, though such high ratios are not practically attainable.1

This behavior is an application of Le Chatelier’s principle, where changes in concentration can shift the equilibrium of a reaction. The reaction involves zinc metal being oxidized to zinc(II) ions and copper(II) ions being reduced to copper metal.23