4.9 Oxidation-Reduction (Redox) Reactions

Redox Reactions

While redox reactions are still a type of reaction, they deserve a subunit of their own due to their uniqueness and difficulty in the AP Chemistry curriculum. Oxidation-Reduction reactions (more commonly known as redox reactions) involve the transfer of electrons between species. These are identified by changes in oxidation numbers. Chemical elements can have different oxidation states; for example, nitrogen can be +5, like in ${N_2O_5}$, or +3, like in ${NO_2^-}$. A species is oxidized when it loses electrons and reduced when it gains electrons. To determine which species is oxidized or reduced, track oxidation numbers from reactants to products. An increase indicates oxidation, while a decrease indicates reduction. Note that elements in their pure form have an oxidation number of 0.