Question

Direct ethanol fuel cells (DEFCs) have shown some promise as a viable option for providing "green" energy to small electrical devices. Calculate E° for the reaction that takes place in DEFCs:

C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l)
Use the following values.

∆G°H2O(l) = -237 kJ/mol
∆G°O2(g) = 0 kJ/mol
∆G°CO2(g) = -394 kJ/mol
∆G°C2H5OH(l) = -175 kJ/mol.
Eo = ? V

Answer 1

The emf of the cell from the reactions and the change in free energy is 2.8 V.

What is the Eocell?

The Eocell refer to the emf of the cell under standard conditions. In this case, it can be obtained from the free energy of the values of the reactants and products.

Now, given; C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l)

ΔG°rxn = [2(-394) + 2( -237)] - [( -175 ) + 0 ]

= [(-788) + (-474)] + 175

= -1087  kJ/mol

Also;

ΔG° = -nFEocell

Eocell  = ΔG° /-nF

Eocell  = -1087  * 10^3/-(4 * 96500)

Eocell  =-1087  * 10^3/386000

= 2.8 V

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