Standard Electrode Potentials (E°)
Standard electrode potentials allow chemists to compare the tendency of different species to gain electrons. This topic underpins electrochemistry in A-Level Chemistry and is essential for predicting reaction feasibility, identifying oxidising and reducing agents, and calculating cell EMF values in electrochemical cells.
Learning Objectives:
Understand how cells are used to measure electrode potentials by reference to the standard hydrogen electrode.
Know that standard electrode potential, E°, refers to conditions of 298K, 100 kPa and 1.00 mol dm-3 solution of ions.
Know the importance of the conditions when measuring the electrode potental, E.
What is an Electric Potential?
An electrode potential describes the tendency of a half-cell to either gain or lose electrons. It can be understood in two equivalent ways:
- As a measure of how easily a substance is oxidised (i.e. how readily it loses electrons).
- As the ability of a half-cell to push electrons away (stronger electron repulsion → stronger tendency to release electrons externally).
Both interpretations are linked through the behaviour of the half-cell equilibrium.
Electrode Potentials and Equilibrium Position
Each half-cell contains a reversible redox equilibrium:
Metal ⇌ Metal ions + electrons