ELECTROCHEMISTRY AND ION CONCENTRATION
Activity dependence of cell voltage:
Measurement of galvanic cell potentials away from the standard state provides a convenient method for measuring ion activity and activity coefficient. As ion concentration is varied in a half-cell to vary ion activity. Equilibrium position of the half cell reduction reaction changes and that causes a change in the half-cell potential. The relationship between the activity and half-cell potential is given by the Nernst equation:
for the general half-cell reduction reaction:
Cells at equilibrium:
When a cell is at equilibrium, Ecell=0 (the 'flat battery' condition) and Q=K, the equilibrium constant for the reaction (see Topic C1). This gives the expression: which allows calculation of equilibrium constants (see Topic C1) for cell reactions from calculated or measured values.
which allows calculation of equilibrium constants for cell reactions from calculated or measured values.