Standard electrode potential

Introduction

The standard electrode potential, also known as redox potential, electrode potential, or simply standard potential, is a measure of the individual potential of a reversible electrode at standard state, i.e., with solutes at an effective concentration of 1 mol/kg, and gases at a pressure of 1 atm. The standard electrode potential is measured in volts (V), and is usually given relative to the standard hydrogen electrode (SHE), which is arbitrarily given a potential of 0.00 V. Electrochemical reactions, particularly redox reactions, involve the transfer of electrons from one species to another.

Thermodynamics and Electrode Potentials

In thermodynamics, the standard electrode potential is closely related to the Gibbs free energy of the reaction. The change in Gibbs free energy (ΔG) for a reaction is related to the standard electrode potential (E) by the equation ΔG = -nFE, where n is the number of moles of electrons transferred and F is the Faraday constant. This relationship allows us to predict the direction of spontaneous reactions in an electrochemical cell.

Standard Hydrogen Electrode

The standard hydrogen electrode (SHE) is a redox electrode which forms the basis of the thermodynamic scale of oxidation-reduction potentials. Its absolute potential is determined by the redox potential of the half-cell reaction under standard conditions, which involves the oxidation or reduction of hydrogen gas. The SHE is commonly used as a reference electrode for measuring the standard electrode potentials of other electrodes.

Measurement of Standard Electrode Potentials

The standard electrode potential of an electrode can be measured by coupling the electrode with a standard hydrogen electrode in an electrochemical cell, and measuring the cell potential. The standard electrode potential is then given by the Nernst equation, which relates the cell potential to the concentrations of the reactants and products.

Significance of Standard Electrode Potentials

Standard electrode potentials provide a quantitative measure of the ability of a species to lose or gain electrons, i.e., its reducing or oxidizing power. They are widely used in electrochemistry for the prediction of the direction of redox reactions, the calculation of the equilibrium constants of reactions, and the determination of the thermodynamic properties of chemical species.

Limitations of Standard Electrode Potentials

While standard electrode potentials provide valuable information about the thermodynamics of reactions, they do not provide information about the kinetics of reactions, i.e., the speed at which reactions occur. Furthermore, standard electrode potentials are measured under standard conditions, and may vary under different conditions.