The following two reactions are known:
Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2(g); ΔH = -26.8 kJ
FeO(s) + CO(g) → Fe(s) + CO2(g) ΔH = -18.5 kJ
The value of ΔH for the following reaction is:
Fe2O3(s) + CO(g) → 2FeO(s) + CO2(g)

Given :
(I) Fe2O3(s)+ 3CO(g) → 2Fe(s) + 3CO2(g); ΔH = -26.8 kJ
(II) FeO(s) + CO(g) → Fe(s) + CO2(g) ΔH = -18.5 kJ
We want to find ΔH for the reaction:
Fe2O3(s) + CO(g) → 2FeO(s) + CO2(g)
Multiply equation (II) by 2:
2FeO(s) + 2CO(g) → 2Fe(s) + 2CO2(g) ΔH = 2(-18.5 kJ) = -37 kJ
Reverse equation (I):
2Fe(s) + 3CO2(g) → Fe2O3(s) + 3CO(g) ΔH = +26.8 kJ
Add the modified equations (II) and (I):
2FeO(s) + 2CO(g) + 2Fe(s) + 3CO2(g) → 2Fe(s) + 2CO2(g) + Fe2O3(s) + 3CO(g)
Simplify:
2FeO(s) + CO(g) → Fe2O3(s) + 2CO(g)
Now, reverse this equation to get the desired equation:
Fe2O3(s) + 2CO(g) → 2FeO(s) + CO(g)
ΔH = -37 kJ + 26.8 kJ = -10.2 kJ
The value of ΔH for the reaction Fe2O3(s) + CO(g) → 2FeO(s) + CO2(g) is approximately -10.3 kJ.