Final answer:
Non-spontaneous redox reactions are characterized by a negative cell potential and the reverse reaction is spontaneous, indicated by a positive voltage, as exemplified by the reaction between copper (II) ions and lead.
Step-by-step explanation:
Non-spontaneous oxidation-reduction (redox) reactions are accompanied by a negative voltage, reflecting their non-spontaneous nature. Spontaneous redox reactions have positive overall voltages, indicating that the process will occur naturally. If the voltage of a redox reaction is negative, the reaction is non-spontaneous in the indicated direction, and the reverse reaction is considered to be spontaneous. A classic example of this is the reaction where copper (II) ions react with metallic lead. The forward reaction is non-spontaneous with an Eforward of -0.47 V, indicating that the spontaneous reaction is actually the reverse, where lead oxidizes copper (II) ions with an Eforward of +0.47 V.