Electrochemical Series

Every entry in the series is a half-reaction quoted with its standard electrode potential, measured against the standard hydrogen electrode assigned a value of zero, under conditions of unit activity and 298 K. Reading the table answers two questions at once. The more positive potential identifies the species more readily reduced, so pairing any two half-reactions shows which will act as the cathode and which as the anode, and the difference between their potentials gives the cell potential. A positive cell potential corresponds to a negative Gibbs free energy change and therefore to a spontaneous reaction. Displacement chemistry follows from the same ordering, a metal higher in the series reducing the ion of one below it, which is why zinc dissolves in copper sulfate solution while copper does not dissolve in zinc sulfate.