Standard Reduction Potentials
Table of standard reduction potentials (E°) at 25°C for common half-reactions. Essential for predicting spontaneity of redox reactions and calculating cell potentials.
| Half-Reaction (Reduction) | E° (V) |
|---|---|
| F2(g) + 2e- → 2F-(aq) | 2.87 |
| H2O2(aq) + 2H+(aq) + 2e- → 2H2O(l) | 1.78 |
| MnO4-(aq) + 8H+(aq) + 5e- → Mn2+(aq) + 4H2O(l) | 1.51 |
| Au3+(aq) + 3e- → Au(s) | 1.5 |
| Cl2(g) + 2e- → 2Cl-(aq) | 1.36 |
| Cr2O72-(aq) + 14H+(aq) + 6e- → 2Cr3+(aq) + 7H2O(l) | 1.33 |
| O2(g) + 4H+(aq) + 4e- → 2H2O(l) | 1.23 |
| Br2(l) + 2e- → 2Br-(aq) | 1.07 |
| NO3-(aq) + 4H+(aq) + 3e- → NO(g) + 2H2O(l) | 0.96 |
| Ag+(aq) + e- → Ag(s) | 0.8 |
| Fe3+(aq) + e- → Fe2+(aq) | 0.77 |
| I2(s) + 2e- → 2I-(aq) | 0.54 |
| Cu2+(aq) + 2e- → Cu(s) | 0.34 |
| SO42-(aq) + 4H+(aq) + 2e- → SO2(g) + 2H2O(l) | 0.2 |
| Cu2+(aq) + e- → Cu+(aq) | 0.15 |
| Sn4+(aq) + 2e- → Sn2+(aq) | 0.15 |
| 2H+(aq) + 2e- → H2(g) | 0 |
| Pb2+(aq) + 2e- → Pb(s) | -0.13 |
| Sn2+(aq) + 2e- → Sn(s) | -0.14 |
| Ni2+(aq) + 2e- → Ni(s) | -0.26 |
| Co2+(aq) + 2e- → Co(s) | -0.28 |
| Fe2+(aq) + 2e- → Fe(s) | -0.44 |
| Cr3+(aq) + 3e- → Cr(s) | -0.74 |
| Zn2+(aq) + 2e- → Zn(s) | -0.76 |
| Mn2+(aq) + 2e- → Mn(s) | -1.18 |
| Al3+(aq) + 3e- → Al(s) | -1.66 |
| Mg2+(aq) + 2e- → Mg(s) | -2.37 |
| Na+(aq) + e- → Na(s) | -2.71 |
| Ca2+(aq) + 2e- → Ca(s) | -2.87 |
| K+(aq) + e- → K(s) | -2.93 |
| Li+(aq) + e- → Li(s) | -3.04 |
Important Notes
- All potentials are measured at standard conditions: 25°C, 1 M concentration, 1 atm pressure.
- The standard hydrogen electrode (SHE) is the reference: E° = 0.00 V by definition.
- More positive E° = stronger oxidizing agent (greater tendency to be reduced).
- More negative E° = stronger reducing agent (greater tendency to be oxidized).
- Cell potential: E°cell = E°cathode − E°anode. A positive E°cell means the reaction is spontaneous.
- To reverse a half-reaction (write it as oxidation), change the sign of E°.
- E° values do NOT change when the half-reaction is multiplied by a coefficient.
- ΔG° = −nFE°cell, where n = moles of electrons transferred and F = 96,485 C/mol (Faraday's constant).