Summary:
- A redox reaction must involve a change in oxidation number for two of the elements involved in the reaction.
- The oxidized element increases in oxidation numbers, while the reduced element decreases.
- Most combination and decomposition reactions are redox reactions since elements are usually transformed into compounds and vice-versa.
- Double-replacement reactions are not redox because ions are simply recombined without any transfer of electrons.
- Acid-base reactions, like the one below, are also notRedox reactions.
- Any reaction in which no oxidation numbers change is not a Redox reaction.