Balance each half-reaction for mass of the species losing or gaining electrons. Balance each half-reaction for charge by adding the correct number of electrons. Balance each half-reaction for all mass by adding water. Add the two half-reactions together and the equation is balanced. Electrochemical Cells and Electromotive Force Electrochemical cells utilize redox reactions.
Electrons flow from a position of high potential energy to low potential energy.
This change in potential energy is just the free energy change for the reaction. Since potential energy is proportional to the the charge of the electron, the free energy change is proportional to the charge AND number of electrons transferred.