In an oxidation/reduction reaction (Redox), electrons are transferred from one chemical species to another. The species which loses electrons is oxidized and is referred to as the reducing agent. The species which gains electrons is reduced and is referred to as the oxidizing agent. Usually, a redox reaction is written as two half-reactions, showing the movement of electrons from one chemical species to another.

Each half-reaction has a standard potential (E) associated with it. The addition of the standard potentials for each half reaction results in a reaction potential (E_rxn). If the overall reaction potential is positive, the redox reaction proceeds to the right. If the overall reaction potential is negative, the redox reaction proceeds to the left.

How can you predict the flow of electrons in a redox reaction? If you have the half-reaction standard potentials, you can calculate the redox reaction potential to determine the flow. If you don't have the potentials, you can mix together the compounds and use your eyes to determine if a reaction occurs. For instance if copper metal loses electrons to form copper 2+ ion, the solution will turn blue.

For more information on redox reactions, please read the chapter on electrochemistry in your lecture text.