Calculate the quantity of heat necessary to reduce $1\;t$ of iron(III) oxide by hydrogen to produce metallic iron. Consult please the → Table of formation enthalpies!
$Fe_2O_3(s)$ $ +$ $3H_2(g)$ $\longrightarrow$ $Fe(s)$ $+$ $3H_2O(l)$
$\Delta H^o $ $ =$ $ 3\Delta H_f(H_2O(l))$ $-$ $\Delta H_f(Fe_2O_3(s))$ $=$ $-33.29 \;kJ$
For the reduction of $1 \;t$ $ =$ $1000000 \;g$ of $Fe_2O_3(s)$, $\frac{33.29\cdot 1000000}{159.69}$ $\approx$ $208500 \; kJ$ heat has to be invested.