A galvanic cell is constructed using a Cu| half-cell and a Zn| half-cell at

CHEMISTRY · Multi-part · A Level · Chemistry · Electrode potentials · Electrode potentials

Problem

A galvanic cell is constructed using a Cu|Cu2+Cu^{2+} half-cell and a Zn|Zn2+Zn^{2+} half-cell at 298 K298\,\text{K}. The two half-cells are initially prepared with the following ion concentrations: • [Cu2+]=0.10 M[\text{Cu}^{2+}] = 0.10\,\text{M} • [Zn2+]=1.0 M[\text{Zn}^{2+}] = 1.0\,\text{M} The standard reduction potentials at 298 K298\,\text{K} are Cu2++2e−→Cu(s)Cu^{2+} + 2e^- \to Cu(s) E°=+0.34 VE^{\text{°}} = +0.34\,\text{V} Zn2++2e−→Zn(s)Zn^{2+} + 2e^- \to Zn(s) E°=−0.76 VE^{\text{°}} = -0.76\,\text{V} (a) Describe qualitatively how decreasing [Cu2+][\text{Cu}^{2+}] from 0.10 M0.10\,\text{M} to 0.010 M0.010\,\text{M} is expected to affect the magnitude of the cell potential. Your explanation should refer to how the system moves relative to equilibrium. (b) For the change in part (a), explain whether the spontaneous direction of electron flow (toward the Cu electrode or toward the Zn electrode) will remain the same or reverse. Justify your answer in terms of the relative values of the reaction quotient QQ and the equilibrium constant KK. (c) Suppose instead that [Zn2+][\text{Zn}^{2+}] is increased from 1.0 M1.0\,\text{M} to 10 M10\,\text{M} while [Cu2+][\text{Cu}^{2+}] remains at 0.10 M0.10\,\text{M}. Predict the effect of this change on the spontaneity of the reaction and explain your reasoning without performing a numerical calculation.

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