Standard Electrode Potential and EMF - NEET Notes, Formula & Common Mistakes

What NEET Asks

• Numerical problems calculating standard cell potential (E°cell).
• Conceptual questions on Standard Hydrogen Electrode (SHE) and its role.
• Identifying anode/cathode based on standard reduction potentials.
• Relationship between E°cell and Gibbs free energy (ΔG°).

Key Points

• Electrode Potential (E): Tendency of an electrode to gain or lose electrons when in contact with its own ions in solution.
• Standard Electrode Potential (E°): Electrode potential measured under standard conditions (1 M ion concentration, 1 atm pressure for gases, 298 K temperature).
• Standard Hydrogen Electrode (SHE): A reference electrode assigned E° = 0.00 V. All other electrode potentials are measured relative to SHE.
• Standard EMF of a Cell (E°cell): The potential difference between the two electrodes of a galvanic cell under standard conditions.
• Convention: Standard reduction potentials are commonly tabulated and used.
• Spontaneity: A redox reaction is spontaneous if E°cell > 0, which corresponds to ΔG° < 0.

Must-Know Formula / Reaction

• E°cell = E°cathode - E°anode
  • E°cell: Standard electromotive force of the cell (Volts).
  • E°cathode: Standard reduction potential of the cathode (Volts).
  • E°anode: Standard reduction potential of the anode (Volts).
• ΔG° = -nFE°cell
  • ΔG°: Standard Gibbs Free Energy change (Joules).
  • n: Number of electrons transferred in the balanced reaction.
  • F: Faraday's constant (96485 C/mol).

Common Mistakes

• Students often use oxidation potential for anode when given reduction potentials. Always use reduction potentials and apply E°cell = E°cathode - E°anode.
• Don't confuse standard conditions (1 M, 298 K, 1 atm) with non-standard conditions where the Nernst equation is required.
• Incorrectly identifying cathode (where reduction occurs, higher reduction potential) and anode (where oxidation occurs, lower reduction potential).

Rapid Revision

E°cell is the potential difference under standard conditions. SHE is the reference (0 V). Calculate E°cell using E°cathode(red) - E°anode(red). A positive E°cell indicates a spontaneous reaction (ΔG° < 0). Remember Faraday's constant for ΔG° calculations.