Electrochemistry and ion concentration, Chemistry

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:

890_electrochemistry.png

for the general half-cell reduction reaction:

 aA+bB+ne-→cC+dD

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.

 

199_electrochemistry1.png

which allows calculation of equilibrium constants for cell reactions from calculated or measured 1046_electrochemistry2.png values.

Posted Date: 7/20/2012 4:43:26 AM | Location : United States







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