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Galvanic (Voltaic) Electrochemical Cells

Key Concepts

  • Galvanic (Voltaic) Cell: a type of electrochemical cell* that converts chemical energy of oxidants and reductants into electrical energy

  • The redox reaction must be spontaneous in order to produce electricity E0 for the galvanic cell is positive.

  • Eo(cell) is the maximum voltage that can be produced by the cell and is also known as electromotive force (emf).

  • A typical galvanic (voltaic) cell consists of

  1. Electrolytes: conducting substances containing the species that take part in the oxidation and reduction reactions.

  2. 2 Electrodes#: conductors used to permit the flow of electrons in an electrochemical cell and provide surfaces at which the oxidation and reduction reactions occur.
        Negative electrode is the anode. Oxidation occurs at the anode.
        Positive electrode is the cathode. Reduction occurs at the cathode.
        Electrons flow from anode to cathode.

  3. Conducting wires, or leads, connect the two electrodes.

  4. Salt bridge: allows for migration of ions to complete the electrical circuit

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Positive electrode (+).

Reduction at cathode.

S+ + e-S

Solid S deposits on cathode.

Consumes electrons.


Negative electrode (-).

Oxidation at anode.

Re- + R+

Solid R electrode disintegrates.

Produces electrons.

Electrons flow to cathode through the conducting wire. electron flow
← ← ← ← ← ← ←
Electrons flow from anode through the conducting wire.
Positive ions migrate to cathode through salt bridge. positive ion flow
← ← ← ← ← ← ←

→ → → → → → →
negative ion flow
Negative ions migrate to anode through salt bridge.

  S+ + e- S   Eo(reduction)
  R R+ + e-   Eo(oxidation)
Redox Reaction
  S+ + R S + R+   Eo(redox) = Eo(reduction) + Eo(oxidation)
Eo(redox) is positive

Animated Tutorial

Example : The Daniell Cell

In 1836 Professor John Daniell adopted a two-cell approach to produce electricity.
The Daniell Cell is divided into 2 half-cells connected by a wire and a salt bridge to complete the electrical circuit.

Cathode Half-cell (+)

electrode : copper metal, Cu(s)

electrolyte : 1M CuSO4(aq)

reduction reaction:
Cu2+(aq) + 2e- → Cu(s)     Eo = +0.35 V

Anode Half-cell (-)

electrode : zinc metal, Zn(s)

electrolyte : 1M ZnSO4(aq)

oxidation reaction:
Zn(s) → Zn2+(aq) + 2e-     E0 = +0.76 V

Cathode half cell: Cu2+(aq) + 2e- Cu(s)   Eo = +0.35 V
Anode half-cell: Zn(s) Zn2+(aq) + 2e-   Eo = +0.76 V
Daniell Cell: Cu2+(aq) + Zn(s) Cu(s) + Zn2+(aq)   Eocell = (+0.35) + (+0.76)
  Eocell = +1.11 V

  • At the negative electrode (anode), zinc is oxidised to zinc ions.

  • The zinc anode disintegrates in time.

  • At the positive electrode (cathode), copper ions are reduced to copper atoms.

  • Copper is deposited on the copper cathode in time.

  • Electrons flow from the zinc anode to the copper cathode.

  • In the overall redox reaction zinc is donating electrons to copper ions.

  • This redox reaction occurs spontaneously, Eo is positive.

  • This redox reaction produces 1.11V of electricity.

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*There are 2 types of electrochemical cells, the galvanic (voltaic) cells discussed here which convert chemical energy into electrical energy, and, electrolytic cells which convert electrical energy into chemical energy.

#The are many different types of electrodes that can be used in galvanic (voltaic) cells. These include:

  • metal-metal ion electrodes (metal is in contact with its ions in solution)
  • gas-ion electrodes (a gas in contact with its anion or cation in solution)
  • metal-insoluble salt-anion electrodes (a metal in contact with one of its insoluble salts and also with a solution containing the anion of the salt)
  • inert, "oxidation-reduction" electrodes (strip of inert conductor such as platinum in contact with a solution containing ions of a substance in two different oxidation states)
  • membrane electrodes (a thin membrane, such as glass, separates the two electrolyte solutions)
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