Cell Diagrams and IUPAC Conventions

Electrochemical cell notation compactly represents the components and directionality of a cell, where a vertical bar denotes a phase interface and a dashed or dotted line denotes the boundary between miscible liquids or a liquid junction.

Species in the same phase are separated by a comma, and a double vertical line denotes an interface where the junction potential is neglected to simplify emf measurements.

Using this cell notation, IUPAC conventions define cell electromotive force, E, as the difference of the open-circuit potentials of the right and left terminals.

A positive cell electromotive force in a cell diagram means that the corresponding cell reaction will spontaneously occur when connected to a load.

Oxidation occurs at the left electrode and reduction at the right electrode. The emf equals the potential of the right electrode minus that of the left electrode. Adding the two half-reactions gives the overall cell reaction.

If the right electrode is the cathode, the reaction is spontaneous; if the left electrode is the cathode, the reverse cell reaction is spontaneous.