A redox reaction, or an oxidation/reduction reaction, occurs when one reactant is oxidized, or loses electrons, and one reactant is reduced, or gains electrons. A simple way to tell the difference is OIL RIG (Oxidation Is Losing; Reducing Is Gaining) or LEO says GER (Lose Electrons - Oxidize; Gain Electrons - Reduce). The oxidizing agent is reduced, and the reducing agent is oxidized. A half-reaction is exactly what it sounds like - half a reaction. It focuses exclusively on one portion of the reaction, either oxidation or reduction.
Redox reactions follow a simple set of steps to solve.
- Split it into 2 half-reactions, one being oxidation and the other being reduction. The reactant being oxidized loses electrons, so they start out without a charge and end up with a positive charge and an electron. The reactant being reduced gains electrons, so they start out charged and with an electron and end up uncharged. Keep in mind that the charge must be neutral on both sides; i.e., should the reducing agent lose 2 electrons, it must end up with a charge of +2 and with 2 extra electrons. Example: Cu (s) ----> Cu2+ + 2 e- An example of a reduction reaction would be 2 Ag+ (aq) + 2 e- ------> 2 Ag (s)
- If it's in an acidic medium...
- Balance all non-hydrogen or oxygen elements
- Balance oxygen by adding H2O to the appropriate side
- Balance hydrogen by adding H+ to the appropriate side
- Balance the charge by adding e-
- Multiply each reaction by an integer so that there are the same number of electrons on each side (i.e. they cancel out)
- Combine the half-reactions and cancel
- If it's in a basic medium, add OH- to each side until all H+ is gone; then, cancel again