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Standard Electrode Potentials for Redox Reactions Tutorial

Some Standard Reduction Potentials

Oxidants

 

Reductants

E0
(volts)

Weakest
Oxidant
K++e K(s) -2.94 Strongest
Reductant
Ba2++2e Ba(s) -2.91
Ca2++2e Ca(s) -2.87
Na++e Na(s) -2.71
Mg2++2e Mg(s) -2.36
Al3++3e Al(s) -1.68
Mn2++2e Mn(s) -1.18
H2O+e ½H2(g)+OH- -0.83
Zn2++2e Zn(s) -0.76
Fe2++2e Fe(s) -0.44
Ni2++2e Ni(s) -0.24
Sn2++2e Sn(s) -0.14
Pb2++2e Pb(s) -0.13
H++e ½H2(g) 0.00
Cu2++2e Cu(s) 0.34
Cu++e Cu(s) 0.52
½I2(s)+e I- 0.54
½I2(aq)+e I- 0.62
Fe3++e Fe2+ 0.77
Ag++e Ag(s) 0.80
½Br2(l)+e Br- 1.08
½Br2(aq)+e Br- 1.10
½Cl2(g)+e Cl- 1.36
½Cl2(aq)+e Cl- 1.40
Strongest
Oxidant
½F2(g)+e F- 2.89 Weakest
Reductant

Key Concepts

  • The standard electrode potential for a redox reaction, Eo(redox), is the sum of the standard electrode potential for the oxidation reaction, Eo(oxidation), and the standard electrode potential for the reduction reaction, Eo(reduction):
    Eo(redox) = Eo(oxidation) + Eo(reduction)

  • Calculating Eo(redox) for a redox reaction:
    X + Y+X+ + Y

  1. Write the two balanced half-reaction equations
    reduction : Y+ + e- → Y
    oxidation : XX+ + e-

  2. Use tabulated values to find the standard electrode potential for each half-equation:
    Y++e-Y   Eo(reduction of Y+)
    XX++e-   Eo(oxidation of X+)
    (Note: Eo(oxidation) = -Eo(reduction))

  3. Add the two half-reaction equations together, and add together their standard electrode potentials:
    Y++e-Y   Eo(reduction of Y+)
    XX++e-   Eo(oxidation of X+)


    Y++XY+X+

    Eo(redox) = Eo(reduction of Y+) + Eo(oxidation of X+)

    Note: changing the stoichiometric coefficients for reactions and products when balancing a redox reaction equation does not change the value of Eo for either the oxidation or the reduction reaction.

 

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Examples

1. Calculate the standard electrode potential, Eo, for the following redox reaction in which all species are present in their standard states:
Zn2+ + Pb → Zn + Pb2+

  1. Write the two balanced half-reaction equations:

        reduction of Zn2+:     Zn2+ + 2e- → Zn

        oxidation of Pb:     Pb → Pb2+ + 2e-

  2. Use tabulated values to find the standard electrode potentail for each half-equation:

        Zn2+ + 2e- → Zn     Eo = -0.76 V

        Pb → Pb2+ + 2e-     Eo = +0.13 V
    (Note: Eo for the oxidation of Pb to Pb2+ is equal to -Eo for the reduction of Pb2+ to Pb)

  3. Add the two half-equations together, and add together their standard electrode potentials:
    Zn2+ + 2e- Zn     Eo = -0.76 V
    Pb Pb2+ + 2e-     Eo = +0.13 V

    Zn2+ + Pb Zn + Pb2+     Eo = (-0.76) + (+0.13) = -0.63 V

2. Calculate the standard electrode potential, Eo, for the following redox reaction in which all species are present in their standard states:

2Ag+ + Cu → 2Ag + Cu2+

  1. Write the two balanced half-reaction equations:

        reduction of 2Ag+:     2Ag+ + 2e- → 2Ag

        oxidation of Cu:     Cu → Cu2+ + 2e-

  2. Use tabulated values to find the standard electrode potentail for each half-equation:

        Ag+ + e- → Ag     Eo = +0.80 V

    So 2Ag+ + 2e- → 2Ag     Eo = +0.80 V
    (Note: changing the stoichiometric coefficients of reactants and products does not change the value of Eo for the reaction.)

        Cu → Cu2+ + 2e-     Eo = -0.34 V
    (Note: Eo for the oxidation of Cu to Cu2+ is equal to -Eo for the reduction of Cu2+ to Cu)

  3. Add the two half-equations together, and add together their standard electrode potentials:
    2Ag+ + 2e- 2Ag     Eo = +0.80 V
    Cu Cu2+ + 2e-     Eo = -0.34 V

    2Ag+ + Cu 2Ag + Cu2+     Eo = (+0.80) + (-0.34) = +0.46 V


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