Electrochemistry (Redox & Electrode Potentials)

Oxidation numbers and redox

Oxidation is loss of electrons (oxidation number increases); reduction is gain (decreases) — OIL RIG. The oxidising agent is reduced; the reducing agent is oxidised. Rules: elements 0; simple ions = charge; O usually −2 (peroxides −1); H usually +1 (metal hydrides −1); the sum equals the overall charge.

Half-equations are combined so electrons cancel, e.g.

$$\text{MnO}_4^{-} + 8\text{H}^{+} + 5e^{-} \rightarrow \text{Mn}^{2+} + 4\text{H}_2\text{O}$$