Question

Define electrode potential and emf of a cell.

Hint:

Electrode potential is a single-electrode property; emf is the potential difference between two electrodes at zero current, \( E_{cell} = E_{cathode} - E_{anode} \).

Answer 1

Step 1: Electrode potential.
When a metal electrode is dipped in a solution of its own ions, a potential difference develops between the metal and the solution due to the tendency of the metal to lose or gain electrons. This potential difference is called the electrode potential. It can be an oxidation potential (tendency to lose electrons) or a reduction potential (tendency to gain electrons). When the ion concentration is 1 M, temperature 298 K and pressure 1 bar, it is called the standard electrode potential \( E^{\circ} \).

Step 2: emf of a cell.
A galvanic cell has two electrodes, an anode (oxidation) and a cathode (reduction). The electromotive force (emf) of the cell is the potential difference between the two electrodes when no current is drawn (open circuit).

Step 3: Express emf.
\( E_{cell} = E_{cathode} - E_{anode} \) (both as reduction potentials), or \( E_{cell} = E_{right} - E_{left} \).

Conclusion: Electrode potential is the potential of a single electrode relative to its solution; emf is the net potential difference between the two electrodes of the cell measured with no current flowing.
\[\boxed{E_{cell} = E_{cathode} - E_{anode}}\]