ΔG = −177Kcal for 2Fe(s) + 32O2(g) → Fe2O3(s) and
What is the Gibbs free energy of formation of Fe3O4 ?;
(i) 2Fe(s) + 32O2(g) → Fe2O3(s)
ΔG = −177 kcal
(ii) 4Fe2O3(s) + Fe(s) → 3Fe3O4(s)
ΔG = −19kcal
ΔGr = 3ΔGF(F3O4) − 4ΔF(Fe2O3) − ΔGF(Fe2S)
3DeltaF(Fe3O4,S) = −19 − 4 × 177.
ΔGF(Fe3O4,S) = 7773 = −242.4kcal/mole