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9.8Thermodynamics and Electrochemistry

Galvanic (Voltaic) and Electrolytic Cells — AP CHEMISTRY Revision Notes & Topical Questions

5 min read 8 parts Lesson 12 of 15 1 quiz

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Lesson summary

9.8 Galvanic (Voltaic) and Electrolytic Cells — AP CHEMISTRY notes: Compare voltaic and electrolytic cells and describe their parts and reactions.Oxidation — occurs at the anode in every cell typeReduction — occurs at the cathode in every cell typeMemory aid — RED CAT, AN OXFeatu…

  • Half-cells
  • Salt bridge
  • Daniell cell
  • Single line
  • Double line
  • Arrangement

Part 1 of 6Redox in cells

Oxidation
  • Oxidation occurs at the anode in every cell type
Reduction
  • Reduction occurs at the cathode in every cell type
Memory aid
  • RED CAT, AN OX

Part 2 of 6Comparison

FeatureVoltaicElectrolytic
ReactionSpontaneous (E° > 0)Non-spontaneous (needs applied voltage)
Anode signNegativePositive
Cathode signPositiveNegative
EnergyProduces electrical energyConsumes electrical energy

Part 3 of 6Voltaic cell

Half-cells
  • Half-cells each has an electrode in a solution of its ions, separated so electrons flow through the external wire
Salt bridge
  • Salt bridge allows ions to flow and completes the circuit
EMF
  • EMF the potential difference between the electrodes, read on a high-resistance voltmeter
Daniell cell
  • Zn | Zn2+ || Cu2+ | Cu with E°cell = +1.10 V

Part 4 of 6Cell notation

Single line
  • Single line a phase boundary
Double line
  • Double line salt bridge
Arrangement
  • Arrangement anode (oxidation) on the left and cathode (reduction) on the right

Part 5 of 6Electrolytic cell: molten salt

Ion movement
  • Ion movement cations move to the cathode and anions to the anode
Cathode
  • Pb2+ + 2e− → Pb
Anode
  • 2Br− → Br2 + 2e−
Rule
  • Rule metals form at the cathode and non-metals at the anode

Part 6 of 6More from the specification

1Charge
  • Q = It, measured in coulombs.
    What the symbols mean: Q = charge (C) · I = current (A) · t = time (s)
2Nernst equation
  • Relates cell potential to standard potential and Q.
3Reaction quotient
  • The ratio of product to reactant concentrations at any moment.
4Electrochemical cell
  • A device linking redox reactions and electricity.
5Standard conditions
  • 298 K and 101 kPa.
6Faraday constant
  • The charge of one mole of electrons, 96 500 C mol-1.
7Equilibrium
  • The state where forward and reverse transfer rates are equal.
8Concentration
  • Moles ÷ volume in dm³, or g/dm³.

Key terms

TermMeaning
AnodeElectrode where oxidation occurs.
CathodeElectrode where reduction occurs.
Salt bridgeConnection completing the circuit with mobile ions.
EMFElectromotive force; cell potential.
ElectrolyteLiquid containing ions that conducts electricity.

Avoid these mistakes

Avoid these mistakes
Thinking oxidation occurs at the cathode in electrolytic cells.
Thinking electrons flow through the salt bridge.
Assuming the anode is always negative.

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