Electrochemistry problems

Question

Use the cell notation below to answer the following question.  

Al (s) │Al+3 (aq) ║ Sn+4 (aq) │ Sn+2 (aq)

1. Write the half reactions that occur at each electrode and the overall reaction that occurs in the cell.

 

2.Calculate the standard cell potential for the reaction.

3.Which type of cell - galvanic or electrolytic - do you anticipate being needed to complete the reaction? Explain your prediction in terms of the cell potential.

4.Calculate the free energy, ΔG, for the reaction. Explain how the free energy supports your prediction from part (c).

Answer 1

First thing is to look up the standard reduction potentials for Al3+ and Sn4+

Al³⁺ + 3e- ==> Al(s) Eº = -1.66 V

Sn⁴⁺ + 2e- ==> Sn²⁺ Eº = +0.15 V

1) Sn⁴⁺ + 2e- ==> Sn²⁺ reduction half reaction (cathode)

Al(s) ==> Al3+ + 3e- oxidation half reaction (anode)

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3Sn⁴⁺ + 2Al(s) ==> 3Sn²⁺ + 2Al³⁺ overall balanced equation

2) Eºcell = 0.15 + 1.66 = 1.81 V

3) Since the cell potential of the cell as written is POSITIVE (+1.81), this voltaic/galvanic cell is sufficient as the reaction is spontaneous. An electrolytic cell (external input of current) is not therefore required.

4) ∆Gº = -nFE

∆Gº = -(6)(96,500)(1.81)

∆Gº = -1048 J

This value of ∆Gº supports the finding in (c) because for a reaction to be spontaneous, ∆Gº must be negative.