Reduction Potentials

The reduction potential of a species is a measure of its ability to reduce, or gain electrons. Technically, there are also oxidation potentials, which measure a species' ability to oxidize, or lose electrons. This is why these are often called redox potentials. However, it is best to express every species by their reduction potential so you don't get confused between the two as much.

Reduction potential is measured in volts(V), equivalent to joules/coulomb(J/C). The potential lets us know how much force is driving the electrons in the wire to the cathode to be reduced by the ions in the cathode. However, you can't express the potential in terms of one species. After all, every redox reaction has both a reducing and oxidizing agent. The expression for the total cell potential of a cell is then as below.

So, when you get a cell, you need to figure out the half-reaction that is oxidization and the half-reaction that is reduction.

What you do is you take the two half-reactions and find the reaction with the smallest potential. Flip this reaction such that the products are now reactants and vice versa. You also have to flip the potential so that it changes sign but not magnitude. Then, the sum of the flipped potential and the other potential is the total cell potential.

You can also find the cell reaction by taking the arrangement explained above and balancing for charge and mass and cancelling out electrons. Note that multiplying a reaction won't affect its reduction potential.