9701 · 24.2
Standard electrode potentials E°, standard cell potentials Ecell and the Nernst equation — FAQ
Frequently asked questions for 9701 Standard electrode potentials E°, standard cell potentials Ecell and the Nernst equation. Direct answers first, then deeper explanation — then practise with marking.
Why is the Standard Hydrogen Electrode's potential exactly 0.00 V?
It is not a measured value but a value defined by international agreement. By setting a universal reference point to zero, we can create a consistent scale to measure and compare the potentials of all other half-cells.
Do I need to memorise all the E° values?
No, you do not need to memorise them. A table of standard electrode potentials is provided in the Data Booklet for your examination.
What happens if the calculated E°cell is zero?
An E°cell of zero means the system is at equilibrium under standard conditions, and ΔG° is also zero. There is no net tendency for the reaction to proceed in either the forward or reverse direction.
Can an electrode potential E° be used to predict the rate of a reaction?
No. Electrode potentials and Gibbs free energy only indicate the thermodynamic feasibility or spontaneity of a reaction. They give no information about the kinetics or rate of reaction, which may be very slow due to a high activation energy.