9701 · 24.2
Standard electrode potentials E°, standard cell potentials Ecell and the Nernst equation flashcards
Revision flashcards for Cambridge 9701 Standard electrode potentials E°, standard cell potentials Ecell and the Nernst equation (syllabus 24.2). Flip, recall, then mark a real past-paper question.
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What is the standard electrode potential, E°?
The potential difference of a half-cell measured against the standard hydrogen electrode (SHE) under standard conditions (298 K, 1 atm pressure for gases, 1.00 mol dm⁻³ concentration for aqueous ions).
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What is the role of the Standard Hydrogen Electrode (SHE)?
It is the universal reference electrode. Its standard electrode potential is defined as exactly 0.00 V, allowing the potentials of all other half-cells to be measured relative to it.
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What does a more positive E° value indicate?
A greater tendency for the species on the left of the half-equation to be reduced. This means it is a stronger oxidising agent.
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What does a more negative E° value indicate?
A lesser tendency for the species on the left to be reduced. This means the species on the right is a stronger reducing agent and is more likely to be oxidised.
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How do you calculate the standard cell potential, E°cell?
E°cell = E°(cathode) - E°(anode). This is equivalent to E°(more positive value) - E°(more negative value). The result must be positive for a spontaneous reaction.
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What occurs at the cathode and anode in an electrochemical cell?
Reduction occurs at the cathode (positive electrode in a voltaic cell). Oxidation occurs at the anode (negative electrode in a voltaic cell). Remember: Red Cat, An Ox.
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What does a positive E°cell value signify?
The reaction is spontaneous (feasible) in the forward direction under standard conditions. The Gibbs free energy change, ΔG°, will be negative.
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What is the relationship between ΔG° and E°cell?
ΔG° = −nFE°cell, where n is the number of moles of electrons transferred in the balanced equation, and F is the Faraday constant (96500 C mol⁻¹).
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What is the purpose of the Nernst equation?
To calculate the electrode potential (E) or cell potential (E_cell) under non-standard conditions (i.e., when concentrations are not 1.00 mol dm⁻³ or pressures are not 1 atm).
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Trap: When calculating E°cell, do I flip the sign for the anode?
No. If you use the formula E°cell = E°(cathode) - E°(anode), you use the standard reduction potential values directly from the data booklet for both half-cells. The subtraction automatically accounts for the oxidation.
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What is the function of the salt bridge in an electrochemical cell?
To complete the electrical circuit by allowing the migration of ions between the two half-cells, maintaining charge neutrality in each beaker. It is typically filled with an inert electrolyte like KNO₃(aq).