Nernst Equation for Electrode Potential
Understand the Nernst equation to calculate electrode potential under non-standard conditions, considering concentration and temperature.
What is Nernst Equation for Electrode Potential?
The potential difference that develops between an electrode and an electrolyte due to the tendency of the electrode material to lose or gain electrons.
Key formula / rule: Nernst Equation (General)
Key points
- To calculate the electrode potential of a cell under non-standard conditions.
- To understand the influence of concentration on electrode potential.
- To apply the Nernst equation to predict cell behavior.
- To relate electrochemical cell potentials to thermodynamic quantities.
Common exam trap
Incorrectly calculating the reaction quotient (Q), especially with solids/liquids or incorrect stoichiometry.
Definitions
- Term
Electrode Potential
- Meaning
The potential difference that develops between an electrode and an electrolyte due to the tendency of the electrode material to lose or gain electrons.
- Term
Standard Electrode Potential (E°)
- Meaning
The electrode potential measured when the concentration of all species is 1 M, the pressure of gases is 1 bar, and the temperature is 298 K.
- Term
Reaction Quotient (Q)
- Meaning
A measure of the relative amounts of products and reactants present in a reaction at a given time; it indicates the direction in which a reaction will proceed to reach equilibrium.
Learning objectives
To calculate the electrode potential of a cell under non-standard conditions.
To understand the influence of concentration on electrode potential.
To apply the Nernst equation to predict cell behavior.
To relate electrochemical cell potentials to thermodynamic quantities.
Formulae
- Name
Nernst Equation (General)
- Note
Where E is electrode potential, E° is standard electrode potential, R is the gas constant, T is temperature in Kelvin, n is the number of moles of electrons transferred, F is Faraday's constant, and Q is the reaction quotient.
- Expression
E = E° - (RT/nF)lnQ
- Name
Nernst Equation (at 298 K)
- Note
Simplified form at standard temperature (298 K or 25°C).
- Expression
E = E° - (0.0592/n)logQ
- Name
Cell Potential
- Note
Applies to the overall cell potential under non-standard conditions.
- Expression
Ecell = E°_cell - (0.0592/n)logQ
- Name
Standard Cell Potential
- Note
Calculated using standard electrode potentials.
- Expression
E°_cell = E°_cathode - E°_anode
- Name
Gibbs Free Energy and Cell Potential
- Note
Relates the change in Gibbs free energy to the cell potential.
- Expression
ΔG = -nFEcell
Prerequisites
Understanding of electrochemical cells (anode, cathode, electrodes).
Concept of standard electrode potential (E°).
Basic thermodynamics (Gibbs free energy).
Knowledge of equilibrium and reaction quotient (Q).
Common mistakes
Incorrectly calculating the reaction quotient (Q), especially with solids/liquids or incorrect stoichiometry.
Using the wrong value for 'n' (number of electrons transferred).
Forgetting to convert standard electrode potential (E°) to the correct units or temperature.
Confusing Ecell with E°_cell.
Incorrectly applying the logarithm term.
Keywords
Nernst Equation
Electrode Potential
Standard Electrode Potential
Reaction Quotient
Electrochemistry
Concentration Cell
Gibbs Free Energy
Practice preview
Which of the following statements about the Nernst equation is INCORRECT?…
medium
For the reaction M^(n+) + ne⁻ → M, what is the term 'Q' in the Nernst equation?…
easy
If the concentration of M^(n+) ions in a half-cell decreases, how does the electrode potential change according to the Nernst equation?…
medium