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cell4Doc Brown's Chemistry  Advanced Level Inorganic Chemistry Periodic Table Revision Notes - Transition Metals

 Appendix 5 Eø Half-cell potentials/reactions, full redox equations and calculating reaction feasibility via Eøreaction

A database of selected half-cell potentials for the 3d-block and transition metals and their ions. How to measure the half-cell potentials is outlined via two diagrams and how to calculate the standard E theta for a reaction is explained with examples and how to deduce the feasibility of a reaction involving a particular transition metal ion.

(c) doc b GCSE/IGCSE Periodic Table Revision Notes * (c) doc b GCSE/IGCSE Transition Metals Revision Notes

INORGANIC Part 10 3d block TRANSITION METALS sub-index: 10.1-10.2 Introduction 3d-block Transition Metals * 10.3 Scandium * 10.4 Titanium * 10.5 Vanadium * 10.6 Chromium * 10.7 Manganese * 10.8 Iron * 10.9  Cobalt * 10.10 Nickel * 10.11 Copper * 10.12 Zinc * 10.13 Other Transition Metals e.g. Ag and Pt * Appendix 1. Hydrated salts, acidity of hexa-aqua ions * Appendix 2. Complexes & ligands * Appendix 3. Complexes and isomerism * Appendix 4. Electron configuration & colour theory * Appendix 5. Redox equations, feasibility, Eø * Appendix 6. Catalysis * Appendix 7. Redox equations * Appendix 8. Stability Constants and entropy changes * Appendix 9. Colorimetric analysis and complex ion formula * Appendix 10 3d block - extended data * Appendix 11 Some 3d-block compounds, complexes, oxidation states & electrode potentials * Appendix 12 Hydroxide complex precipitate 'pictures', formulae and equations

Advanced Level Inorganic Chemistry Periodic Table Index * Part 1 Periodic Table history * Part 2 Electron configurations, spectroscopy, hydrogen spectrum, ionisation energies * Part 3 Period 1 survey H to He * Part 4 Period 2 survey Li to Ne * Part 5 Period 3 survey Na to Ar * Part 6 Period 4 survey K to Kr and important trends down a group * Part 7 s-block Groups 1/2 Alkali Metals/Alkaline Earth Metals * Part 8  p-block Groups 3/13 to 0/18 * Part 9 Group 7/17 The Halogens * Part 10 3d block elements & Transition Metal Series * Part 11 Group & Series data & periodicity plots * All 11 Parts have their own sub-indexes near the top of the pages

Appendix 5. Eø Half-cell potentials/reactions, full redox equations and calculating feasibility via Eøreaction

Database of Standard Electrode Potentials, Eø values

See also Appendix 11 for more on electrode potential charts

  • For those mentioned on this web page for aqueous systems under standard conditions,

  • i.e. at 298K, 1 mol dm-3 concentration (aq), 1 atm. reactant gas pressure (if appropriate),

  • and compared with the half-cell potential for the standard hydrogen gas-hydrogen ion electrode (via Pt electrode interface),

    • which is assigned the arbitrary convention value of EøH+(aq)/H2(g) = 0.00 V

      • 2H+ (aq) + 2e-  H2 (g) 

    • Details on Part 7. Equilibria - Redox systems (opens in new window)

    • Half-cell electrode potential equations are usually quoted as a reduction (as above and list below)

  • The half-cell potentials are listed downwards from the strongest reducing agent system (most negative Eø/V) to the strongest oxidising agent system (the most positive Eø/V):

    • The oxidation state changes are also shown for each half-cell redox potential.

    • -0.76 for Zn2+(aq) + 2e- Zn(s)  [Zn(II) ==> Zn(0)]

    • -0.56 for Fe(OH)3(s) + e- Fe(OH)2(s) + OH-(aq)  [Fe(III) ==> Fe(II), in alkali]

    • -0.44 for Fe2+(aq) + 2e- Fe(s)  [Fe(II) ==> Fe(0)]

    • -0.41 for Cr3+(aq) + e- Cr2+(aq)  [Cr(III) ==> Cr(II), in acid]

    • -0.26 for V3+(aq) + e- V2+(aq)  [V(III) ==> V(II), in acid]

    • -0.10 for [Co(NH3)6]3+(aq) + e- [Co(NH3)6]2+(aq)   [Co(III) ==> Co(II) for NH3 ligand]

    • 0.00 for 2H+(aq) + 2e-  H2(g)  [the arbitrary assumed standard value, H(+1) ==> H(0)]

    • +0.34 for VO2+(aq) + 2H+(aq) + 2e- V3+(aq) + H2O(l)  [V(IV) ==> V(III)]

    • +0.40 for 1/2O2(g) + H2O(l) + 2e-  2OH-(aq)  [O(0) ==> O(-2), in alkali]

    • +0.54 for I2(aq) + 2e- 2I-(aq)  [I(0) ==> I(-1)]

    • +0.68 for O2(g) + 2H+(aq) + 2e- ==> H2O2(aq)  [O(0) ==> O(-1)

    • +0.77 for Fe3+(aq) + e- Fe2+(aq)  [Fe(III) ==> Fe(II), in acid]

    • +0.80 for Ag+(aq) + e- ==> Ag(s) (Ag(i) ==> Ag(0)]

    • +1.00 for VO2+(aq) + 2H+(aq) + 2e- VO2+(aq) + H2O(l)  [V(V) ==> V(IV) in acid]

    • +1.23 for 1/2O2(g) + 2H+(aq) + 2e-   H2O(l)  [O(0) ==> O(-2), in acid???]

    • +1.33 for Cr2O72-(aq) + 14H+(aq) + 6e- 2Cr3+(aq) + 7H2O(l)  [Cr(VI) ==> Cr(III)]

    • +1.36 for Cl2(aq) + 2e- 2Cl-(aq)  [Cl(0) ==> Cl(-1)]

    • +1.51 for MnO4-(aq) + 8H+(aq) + 5e- Mn2+(aq) + 4H2O(l)  [Mn(VII) ==> Mn(II)]

    • +1.52 for Mn3+(aq) + e- Mn2+(aq) + H2O(l)  [Mn(III) ==> Mn(II)]

    • +1.77 for H2O2(aq) +  2H+(aq) + 2e- 2H2O(l)  [O(-1) ==> O(-2), in acid?]

    • +1.82 for Co3+(aq) + e- Co2+(aq)  [Co(III) ==> Co(II) for H2O ligand]

    • +2.01 for S2O82-(aq) + 2e- 2SO42-(aq)  [2O(-1) ==> 2O(-2)]

    • -

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How standard electrode potentials are determined

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Electrode Potential Chart for the 3d-block transition metals

Advanced Inorganic Chemistry Page Index and Links

 

Calculation of Eø for a redox reaction

  • In principle, any accurately known half-cell potential can be used in a cell system to obtain an unknown half-cell potential which can be used to theoretically predict the feasibility of a reaction.

  • The electrochemical series and electrode potential charts, know how to construct, read and use them.

  • Other half-cells, they don’t have to simple metal/ metal ions, all you need is two interchangeable oxidation states eg Cl2(aq)/Cl-(aq) or Mn2+(aq)/MnO4-(aq) etc. but both components of the half-cell must be in the same solution and in contact with a platinum electrode that connects to the rest of the circuit.

  • One way of working out Eø values for a complete reaction:

    • Eøcell (reaction) =  Eø(red) – Eø(ox)   ... where ...

    • Eø(red) is the half-cell potential of the reduction 'half-reaction'

    • Eø(ox) is the half-cell potential of the oxidation 'half-reaction'

    • which amounts to the difference between the half-cell potentials on an electrode potential chart.

    • If you consider the copper-zinc cell for the overall reaction

      • Cu2+(aq) + Zn(s) ==> Cu(s) + Zn2+(aq)

    • Eø(red) is the most positive or the least negative = the strongest oxidising agent or electron acceptor of the two half-cell systems.

      • It is the +ve battery pole, eg Cu/Cu2+ (+0.34V) compared to Zn/Zn2+ (-0.76V).

      • so the Cu2+(aq) + 2e- ==> Cu(s) reduction occurs rather than reduction of Zn2+ to Zn.

    • Eø(ox) is the least positive or the most negative = the strongest reducing agent or electron donor of the two half-cell potentials.

      • It is the -ve battery pole eg Zn/Zn2+ compared to Cu/Cu2+,

      • so the Zn(s) - 2e- ==> Zn2+(aq) oxidation happens rather than oxidation of Cu to Cu2+.

    • For overall cell redox reaction: Cu2+(aq) + Zn(s) ==> Cu(s) +Zn2+(aq)  

    • Calculating the voltage-Emf for the copper-zinc cell: 

      • Eø(red) = EøCu(s)/Cu2+(aq) = +0.34V, Eø(ox) = EøZn(s)/Zn2+(aq) = -0.76V

      • Eøcell =  Eø(red) – Eø(ox)= +0.34V - (-0.76) = + 1.10 V (feasible!)

      • Eøoverall cell reaction must be >0 for the reaction to be feasible

For more details and examples see

Equilibrium Part 7 Redox equilibria, half-cell electrode potentials, electrolysis and electrochemical series

Scandium * Titanium * Vanadium * Chromium * Manganese * Iron * Cobalt * Nickel * Copper * Zinc * Silver & Platinum

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Introduction 3d-block Transition Metals * Appendix 1. Hydrated salts, acidity of hexa-aqua ions * Appendix 2. Complexes & ligands * Appendix 3. Complexes and isomerism * Appendix 4. Electron configuration & colour theory * Appendix 5. Redox equations, feasibility, Eø * Appendix 6. Catalysis * Appendix 7. Redox equations * Appendix 8. Stability Constants and entropy changes * Appendix 9. Colorimetric analysis and complex ion formula * Appendix 10 3d block - extended data * Appendix 11 Some 3d-block compounds, complexes, oxidation states & electrode potentials * Appendix 12 Hydroxide complex precipitate 'pictures', formulae and equations

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