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Question
Write the IUPAC convention for calculating the standard emf of a cell.
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Solution
According to the IUPAC convention, the standard emf (electromotive force) of a cell is given by:
\[\ce{E{^{\circ}_{cell}} = E{^{\circ}_{cathode}} - E{^{\circ}_{anode}}}\]
This means the standard EMF of an electrochemical cell is calculated by subtracting the standard electrode potential of the anode (oxidation half-cell) from that of the cathode (reduction half-cell).
All standard electrode potentials (E°) used are reduction potentials as given in the electrochemical series.
Example of daniell cell:
\[\ce{Zn ∣ Zn^2+(1M) ∣∣ Cu^2+ (1M) ∣ Cu}\]
From electrochemical series:
\[\ce{E{^{\circ}_{cathode}}}\] = +0.34V
\[\ce{E{^{\circ}_{anode}}}\] = −0.76V
\[\ce{E{^{\circ}_{cell}}}\] = +0.34 − (−0.76) = +1.10 V
Since \[\ce{E{^{\circ}_{cell}}}\] is positive, the reaction is feasible.
