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The electromotive force

المؤلف:  Peter Atkins، Julio de Paula

المصدر:  ATKINS PHYSICAL CHEMISTRY

الجزء والصفحة:  ص218-219

2025-11-18

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The electromotive force

The current produced by a galvanic cell arises from the spontaneous chemical reaction taking place inside it. The cell reaction is the reaction in the cell written on the assumption that the right-hand electrode is the cathode, and hence that the spontaneous reaction is one in which reduction is taking place in the right-hand compartment. Later we see how to predict if the right-hand electrode is in fact the cathode; if it is, then the cell reaction is spontaneous as written. If the left-hand electrode turns out to be the cathode, then the reverse of the corresponding cell reaction is spontaneous. To write the cell reaction corresponding to a cell diagram, we first write the right-hand half-reaction as a reduction (because we have assumed that to be spontaneous). Then we subtract from it the left-hand reduction half-reaction (for, by implication, that electrode is the site of oxidation). Thus, in the cell Zn(s) |ZnSO4(aq) || CuSO4(aq)|Cu(s) the two electrodes and their reduction half-reactions are Right-hand electrode: Cu²⁺(aq) + 2 e⁻ → Cu(s) Left-hand electrode: Zn²⁺(aq) + 2 e⁻ → Zn(s) Hence, the overall cell reaction is the difference: Cu²⁺(aq) + Zn(s) →Cu(s)+Zn²⁺(aq)