(i) 2Fe2O3( s)→4Fe(s)+3O2( g); ΔrG∘=+1487.0 kJ mol−1 (ii) 2CO(g)+O2( g)→2CO2 (g) ΔrG∘=−514.4 kJ mol−1 Multiple reaction (ii) with 3 , we get (iii) 6CO(g)+3O2( g)→6CO2( g); ΔrG∘=3×−514.4=−1543.2kJmol−1 When we add reaction (i) and reaction (iii), we get reaction (iv) (iv) 2Fe2O3( s)+6CO(g)⟶ 4Fe(s)+6CO2( g) Free energy change, ΔrG∘ for the reaction will be 1487.0−1543.2=−56.2 kJ mol−1