Electrochemistry

Redox Foundations

Assign oxidation states by the priority rules (free elements zero, oxygen $-2$, hydrogen $+1$ with nonmetals) and track electrons with OIL RIG: oxidation is loss, reduction is gain. The oxidizing agent is itself reduced; the reducing agent is oxidized. Balance redox equations as half-reactions, equalizing electrons before adding.

Galvanic and Electrolytic Cells

A galvanic (voltaic) cell runs a spontaneous reaction to produce current; an electrolytic cell consumes external current to drive a nonspontaneous one. In BOTH, oxidation occurs at the anode and reduction at the cathode (AN OX, RED CAT); the salt bridge maintains neutrality. Cell potential comes from reduction potentials: $E_{cell}^{\circ }=E_{cathode}^{\circ }-$ A positive means spontaneous, linked to free energy by