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: Meaning of electrode potential.
Every electrode-solution boundary sets up a charge separation because the metal atoms tend either to enter the solution as ions (leaving electrons behind) or to deposit from solution. The resulting voltage of that single half-cell is its electrode potential. Measured under standard conditions (1 M, 298 K, 1 bar) it becomes the standard electrode potential.

Step 2: Meaning of emf.
Join two half-cells and the difference in their tendencies to attract electrons produces a driving voltage that pushes electrons through the external wire. This maximum voltage, measured when the circuit carries no current, is the cell's emf.

Step 3: Relation.
\(E_{cell} = E_{cathode} - E_{anode}\); a positive value means the cell reaction is spontaneous.
\[\boxed{\text{Electrode potential} \to \text{half-cell};\ \text{emf} \to \text{whole cell}}\]