આથી, $\Delta H$$_{reaction}$ = [$\Sigma$$\Delta$$H_f$$^o$ of product - $\Sigma$$\Delta$$H_f$$^o$ of reactant]
$[(2 ×$ $\Delta$$H_f$$^o$ $of Fe(s) + 3 $ $\Delta$$H_f$$^o of$ $CO_2$ $(g) -$ ($\Delta$$H_f$$^o of$ $Fe_2O_3(s) + 3 × $ $\Delta$$H_f$$^o of CO_{(g)}]$
$-6.6 = [(2 × 0) + (3 × -94) - $ ($\Delta$$H_f$$^o$ of $Fe_2O_3$${(s)} + 3 × -26.4)] \,kcal$
$-6.6 = [0 - 282 - $ $\Delta$$H_f$$^o of$ $Fe_2O_3{(s)} + 79.2]$
$Fe_2O_3 (s)$ માટે $\Delta$$H_f$$^o$ $= -196.2 \,Kcal/mol$
$CO_2(g) , CO(g)$ અને $H_2O(g)$ માટે $\Delta H^o_f$ના મૂલ્યો અનુક્રમે $-393.5, -110.5$ અને $-241.8\, kJ/mol$,
$CO_2(g) + H_2(g) \to CO(g) + H_2O(g)$ is :