Calculating delta G and standard cell potential

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4NH3 (g) + 3O2(g) --> 2N2 (g) + 6H2O

equations : ∆G = ∆Gf of products - ∆Gf of reactants -------> standard state conditions
∆H = ∆Hf of products - ∆Hf of reactants
∆S = ∆Sf of products - ∆Sf of reactants
∆G = -nF (Ecell)
∆G = ∆H - T∆S

constants : Faraday's constant --> F = 96500 C/mol e
there are 12 e transferred from anode to cathode therefore n = 12 e
note : please check the 3rd page of the attached pdf file for the equations of the
anode and cathode showing ...