PHYSICAL CHEMISTRY IN BRIEF

CHAP. 11: ELECTROCHEMISTRY [CONTENTS] 405

Example

A silver electrode coated with a layer of solid silver chloride (a silver chloride electrode) is dipped

into a solution of hydrogen chloride of the molalitym.

Partial reactions:

AgCl(s) = Ag++ Cl−, Ag++ e−= Ag(s).

Overall reaction:

AgCl(s) + e−= Ag(s) + Cl−.

Nernst equation:

Φ = Φ◦−

RT

F

ln

mγ±

mst

.

Note: Half-cells of the second type are used as so-calledreferential electrodesto de-

termine standard potentials of other half-cells. Compared with the standard hydrogen

electrode (see11.8.6) which was chosen for the definition of half-cell potentials, refer-

ential electrodes offer a number of practical benefits. Their potentials in relation to the

standard hydrogen electrode are measured very accurately.

11.8.10.4 Gas half-cell

An inert electrode is washed by a gas. In the electrolyte there are ions (either anions or cations)
of this gas.