What does E°cell represent in electrochemistry?

• A. The actual measured potential under nonstandard conditions
• B. The theoretical cell potential under standard conditions (1 M, 25°C, activities 1)
• C. The energy required to start the reaction
• D. The potential of the cathode only

Answer: (B)

E°cell is the standard cell potential: the potential difference you would obtain for the overall electrochemical cell when all species are in their standard states (typically 1 M solutions, 1 atm gases, and 25°C). It’s a theoretical value determined from the standard reduction potentials of the two half-reactions and reflects how favorable the reaction is under these standard conditions. The standard cell potential is found from the difference between the cathode and anode standard potentials (E°cell = E°cathode − E°anode). Because it assumes standard states, it doesn’t depend on actual concentrations or pressures; under real conditions the observed potential E differs and is related to E°cell by the Nernst equation. E°cell also connects to energy via ΔG° = −nFE°cell, linking electrical potential to the reaction’s standard Gibbs free energy change. It’s not the actual potential under nonstandard conditions, not the energy to start the reaction, and not the cathode potential alone.