Redox and electrochemistry
Join two half-cells and read off the voltage — and which way it runs.
Scientific learning path
- 01UnderstandLive
- 02ExploreLive
- 03ExperimentLive
- 04ObserveLive
- 05ExplainLive
- 06ApplyLive
- 07TestBuilding
The reactivity series
- Li+/Li-3.04 V
- K+/K-2.93 V
- Ca2+/Ca-2.87 V
- Na+/Na-2.71 V
- Mg2+/Mg-2.37 V
- Al3+/Al-1.66 V
- Zn2+/Zn-0.76 V
- Fe2+/Fe-0.44 V
- Ni2+/Ni-0.25 V
- Pb2+/Pb-0.13 V
- H+/H20 V
- Cu2+/Cu0.34 V
- I2/I-0.54 V
- Ag+/Ag0.8 V
- Br2/Br-1.09 V
- Cl2/Cl-1.36 V
- F2/F-2.87 V
Description of this simulation
Copper(II) has the more positive standard potential at 0.34 volts, so it is reduced and is the cathode. Zinc at -0.76 volts is oxidised and is the anode. The cell potential is 1.1 volts, and 2 electrons pass in the balanced equation. That gives a free energy change of -212.27 kilojoules per mole, which is negative — the reaction is spontaneous in this direction.
1.1 V
Runs on its own
- Cathode, reduced
- Copper(II) 0.34 V
- Anode, oxidised
- Zinc -0.76 V
- Electrons transferred
- 2
- Free energy change
- -212.27 kJ/mol
If you name the electrodes yourself
Choosing the electrodes the other way round gives -1.1 volts. A negative cell potential is not a mistake to be corrected with a modulus sign — it is the reaction telling you the spontaneous direction is the reverse one.
Doubling the equation
E
1.1 V
unchanged
ΔG
-424.54 kJ/mol
doubled
Multiplying a half-equation through by two doubles the free energy change and leaves the voltage exactly where it was. E is energy per electron — an intensive property — and treating it like an extensive one is the commonest error in electrochemistry.
The reactivity series
Not a list to memorise: it is the potential table in order. A metal displaces any metal below it because its reduction potential is more negative, and every metal above hydrogen displaces hydrogen from acid.
Zinc displaces Copper(II)
What this model shows — and what it simplifies
Educational ModelStandard reduction potentials at 298 K against the standard hydrogen electrode, one sign convention throughout — oxidation potentials are never stored, only negated where needed, so the two cannot be mixed.
Where do we see this in real life?
Every battery is this arithmetic. So is galvanic corrosion: bolting two different metals together in a damp place builds a cell, and the more reactive one is consumed to protect the other — which is exactly how a sacrificial anode on a ship works.