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Standard reduction potentials (E°) for different half-cells are given: E°(Cu²+/Cu) = +0.34 V, E°(Zn²+/Zn) = -0.76 V E°(Ag⁺/Ag) = +0.80 V, E°(Mg²+/Mg) = -2.37 V For which cell is delta_G° per mole of electrons the most negative?

1. Zn(s) | Zn²+(1M) || Mg²+(1M) | Mg(s)
2. Zn(s) | Zn²+(1M) || Ag^+(1M) | Ag(s)
3. Cu(s) | Cu²+(1M) || Ag^+(1M) | Ag(s)
4. Ag(s) | Ag^+(1M) || Mg²+(1M) | Mg(s)

Correct answer: Zn(s) | Zn²+(1M) || Ag^+(1M) | Ag(s)

Solution

delta_G° per mole of electrons = -F*E°_cell. For delta_G°/n to be most negative, E°_cell must be maximum. Cell B (Zn|Ag): E° = E°_cathode - E°_anode = 0.80 - (-0.76) = 1.56 V. This is the highest among the spontaneous cells, giving delta_G°/n = -F * 1.56 = most negative.

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