A redox reaction is a reaction where the reactants upon reacting, one species becomes oxidised, whereas another becomes reduced; the two reactions are complementary to each other. The oxidizing agent is the molecule or ion in the reaction which accepts electrons (gets reduced). By reducing, the oxidising agent causes the other reactant to lose electrons; this second reactant is called the reducing agent, as it is donating electrons (gets oxidised) to the oxidising agent. It occurs due to the movement of electrons from one species to another. Losing electrons causes oxidation and gaining electrons causes reduction.
For example, reacting chlorine with potassium iodide forms potassium chloride and iodine:
- Cl2 + 2KI --> 2KCl + I2
We can also show this reation in half equations, it is easier to see how reduction and oxidation occurs.
- Cl2 + 2e- --> 2Cl- This is reduction as 2 electrons are gained. The chlorine becomes chloride (gains a negative charge).
- 2I- --> I2 + 2e- This is oxidation as 2 electrons are lost. Iodide becomes iodine (no longer has a charge).
This is also an example of a displacement reaction. Chlorine is more reactive than iodine allowing transfer of electrons.
- ↑ Libretexts [internet], Chemistry: Oxidation-Reduction reactions, 1.1, Last edited June 2018 [cited 5 December 2018]. Available from: https://chem.libretexts.org/Textbook_Maps/Analytical_Chemistry/Supplemental_Modules_(Analytical_Chemistry)/Electrochemistry/Redox_Chemistry/Oxidation-Reduction_Reactions