These two make up the two halves of an electrochemical cell. A comparison of the electron attraction of these two half-cells becomes the electrode potentials. The cell works because the valence electrons of zinc have a higher energy than the valence electrons of copper. This gives zinc a greater tendency to give up electrons than copper. In the external circuit, electrons will always move from the positive anode to the negative cathode.
Oxidation always occurs at the anode.
This is a reduction half-reaction. Reduction always occurs at the cathode. These electrons move from the anode to the cathode through the external circuit . SO 4 -2 ions in solution move from the cathode to the anode through the salt bridge . The cell continues to operate as long as there is a potential energy difference between the half-cells.