Electro Chemistry

Question

Calculate the non-standard cell potential (in V) for the following reaction at 887.79 ℃ with the following concentrations: [Mg^+2] = 6.50×10^−2 M; [Cu^+2] = 1.30×10^−5 M

Cu^+2(aq) + Mg(s) ----> Cu(s) + Mg^+2(aq)

Answer 1

For non-standard conditions, we need to use the Nernst equation:

E_cell = Eº_cell - RT/nF ln Q

First, we'll find Eº_cell:

Cu²⁺ + 2e- ==> Cu(s) Eº = 0.34 V

Mg²⁺ + 2e- ==> Mg(s) Eº = -2.38 V

Eº_cell = 0.34 + 2.38 = 2.72 V

Next, we'll find Q (the reaction quotient):

Q = [Mg²⁺] / [Cu²⁺] = 6.50x10^-2 M / 1.30x10^-5 M = 5x10³

Finally use the Nernst equation to solve for E_cell:

R = 8.314 J/Kmol; T = 887.79 + 273.15 = 1160.94K; n = 2 mols e-; Q = 5x10³; Eº = 2.72 V

Ecell = Eº - RT/nF ln Q

Ecell = 2.72 - (8.314)(1160.94K) / (2)(96,485) ln Q

Ecell = 2.72 - 0.0500 ln 5x10³

Ecell = 2.72 - 0.43

Ecell = 2.29 V