9.3Thermodynamics and Electrochemistry
Electrochemical Cells — AP CHEMISTRY Revision Notes & Topical Questions
5 min read 9 parts Lesson 7 of 15 Unit quiz
Lesson summary
9.3 Electrochemical Cells — AP CHEMISTRY notes: Compare voltaic and electrolytic cells and calculate cell potential, free energy and the effect of concentration.FeatureVoltaicElectrolyticReactionSpontaneousDriven by applied voltageAnodeOxidation, negativeOxidation, positiveCathod…
- Half-cells
- Salt bridge
- Standard hydrogen electrode
- ΔG° = −nFE°cell
- Equilibrium
- Nernst equation
Section 1 of 9Cell types
| Feature | Voltaic | Electrolytic |
|---|---|---|
| Reaction | Spontaneous | Driven by applied voltage |
| Anode | Oxidation, negative | Oxidation, positive |
| Cathode | Reduction, positive | Reduction, negative |
Section 2 of 9Voltaic cell
Half-cells
- Half-cells electrodes in solutions of their ions
Salt bridge
- Salt bridge completes the circuit; electrons flow in the external wire from anode to cathode
Notation
- Notation anode | anode ion || cathode ion | cathode
Section 3 of 9Standard cell potential
Standard cell potential
Standard hydrogen electrode
- 0.00 V
E°cell
- E°cathode − E°anode
Feasible
- Feasible positive E°cell means the reaction is favoured
Section 4 of 9Free energy
ΔG°
−nFE°cell
- negative ΔG° for positive E°
Equilibrium
- E = 0 when Q = K
Section 5 of 9Nonstandard conditions
Nernst equation
- E = E° − (0.0592/n) log Q at 298 K
Concentration cell
- E° = 0 and E arises from the concentration difference
Section 6 of 9Electrolysis
Charge
- Q = It and n(e−) = Q/F
Molten salts
- Molten salts metal at the cathode and non-metal at the anode
Section 7 of 9More from the specification
Reaction quotient
- The ratio of product to reactant concentrations at any moment.
Standard conditions
- 298 K and 101 kPa.
Faraday constant
- The charge of one mole of electrons, 96 500 C mol-1.
Section 8 of 9Key terms
| Term | Meaning |
|---|---|
| Voltaic cell | Produces electricity from a spontaneous reaction. |
| Electrolytic cell | Uses electricity to drive a reaction. |
| E°cell | Cathode potential minus anode potential. |
| Nernst equation | Gives E for nonstandard concentrations. |
Section 9 of 9Exam technique
Avoid these mistakes
Mixing up which electrode carries oxidation.
Subtracting E° values in the wrong order.
Multiplying E° by coefficients.
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