The following two reactions are known Fe₂O₃(s) + 3CO(g) → 2Fe(s) + 3CO₂(g); ∆H = –26.8 kJ FeO(s) + CO(g) → Fe(s) + CO₂(g); ∆H = – 16.5 kJ The value of ∆H for the following reaction Fe₂O₃(s) + CO(g) → 2FeO(s) + CO₂(g) is (Mains 2010)

Fe₂O₃(s) + 3CO(g) → 2Fe(s) + 3CO₂(g); ∆H = – 26.8 kJ ...(i) FeO(s) + CO(g) → Fe(s) + CO₂(g); ∆H = – 16.5 kJ ...(ii) Fe₂O₃(s) + CO(g) → 2FeO(s) + CO₂(g); ∆H = ?..(iii) Eq. (iii) can be obtained as : (i) – 2(ii) = –26.8 – 2(–16.5) = –26.8 + 33.0 = +6.2 kJ