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Question

The following electrochemical cell is set up at 298K:
Zn/Zn2+(aq)(1M)//Cu2+(aq)(1M)/Cu
Given EoZn2+/Zn=0.761V,EoCu2+/Cu=+0.339V
(1) Write the cell reaction.
(2) Calculate the emf and free energy change at 298K.

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Solution

(1) Oxidation at anode: Zn(s)Zn2+(aq)+2e
Reduction at cathode: Cu2+(aq)+2eCu(s)
Net cell reaction
Zn(s)+Cu2+(aq)Zn2+(aq)+Cu(s)
(2) Eocell=EoCuEoZn
Eocell=0.339(0.761)
Eocell=+1.1V
Since the concentrations of the ions are 1M,
Ecell=Eocell=+1.1V
The free energy change ΔG=nFEcell
ΔG=2×96500×1.1
ΔG=212300J
ΔG=212kJ
because 1kJ=1000J

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