A concentration cell is built based on the following half reactions by using two pieces of zinc as electrodes, two Zn2+ solutions, 0.129 M and 0.427 M, and all other materials needed for a galvanic cell. What will the potential of this cell be when the cathode concentration of Zn2+ has changed by 0.047 M at 291 K?

Zn2+ + 2 e- ? Zn Eo = -0.761 V

Respuesta :

Explanation:

The given reaction at cathode will be as follows.

At cathode: [tex]Zn^{2+} + 2e^{-} \rightarrow Zn[/tex],     [tex]E_{o}[/tex] = -0.761 V

At anode: [tex]Zn \rightarrow Zn^{2+} + 2e^{-}[/tex],       [tex]E_{o}[/tex] = 0.761

Therefore, net reaction equation will be as follows.

                 [tex]Zn^{2+} + Zn \rightarrow Zn + Zn^{2+}[/tex]

Initial:     0.129         -            -       0.427

Change:  -0.047      -            -     -0.047

Equilibrium: (0.129 - 0.047)      (0.427 - 0.047)

                = 0.082                       = 0.38

As [tex]E^{o}_{cell}[/tex] for the given reaction is zero.

Hence, equation for calculating new cell potential will be as follows.

                   E_{cell} = [tex]E^{o}_{cell} - \frac{RT}{nF} ln \frac{[Zn^{2+}]_{products}}{[Zn^{2+}]_{reactants}}[/tex]

                              = [tex]0 - \frac{8.314 atm L/mol K \times 291 K}{2 \times 96500} ln \frac{0.38}{0.082}[/tex]

                              = 0.019

Thus, we can conclude that the cell potential of the given cell is 0.019.