Voltage, a measure of the strength of an electric current, represents the force that moves electrons
from the anode to the cathode in a voltaic cell. When a greater force (voltage) is applied in
the opposite direction, electrons can be pushed from what would normally be the cathode toward
the voltaic cell’s anode. This process is called electrolysis. In a broader sense, electrolysis is
the process by which a redox reaction is made to occur in the nonspontaneous direction.
For example, sodium metal reacts readily with chlorine gas to form sodium chloride, but we do not
expect sodium chloride, as it sits in our saltshakers, to decompose into sodium metal and
chlorine gas. We say the forward reaction below is spontaneous, and the reverse reaction is
nonspontaneous.