Question

Consider a fuel cell that uses the reaction of ethanol with oxygen to produce electricity,
CH3CH20H(l)+ 3O2(g)---> 2CO2(g)+3H2O

Use thermodynamic data to determine the value of E°cell for this cell at 25 °C.

I don't really know where to start. I got the standard G for
CH3CH2OH: -174.8 kJ/mol
O2: 0 kJ/mol
CO2: -394.4 kJ/mol
H2O: -237.1

I was thinking maybe I should use deltaG = deltaG(products)- deltaG(reactants).

Then use the equation of of deltaG = -nFEcell and manipulate it to Ecell=deltaG/-nF, but then I don't know how many n is transferred.
Can someone please help me with the problem? I don't really understand how to do it.

Answer 1

Yes you do exactly what you have outlined. I would look at change in C and change in O for n. If we see ethanol as C2H6O and assign oxiatioin states of -2 for O and +6 for 6H, that makes 2 C in ethanol as -4. On the right the 2C are +8 so the change in e is 12. We can check that number with O to make sure we're right. We have 1O in ethanol which we called -2 and it is -2 in CO2 and H2O so it hasn't changed at all. That leaves us with 6 O on the left at zero going to 6 O on the right at -2 each or 6*2 = 12 so O has changed by 12 e. That checks. n must be 12

Answer 2

its still not making sense to me

Answer 3

Bad explanation, but it's correct answer.