$2Al + C{r_2}{O_3} \to A{l_2}{O_3} + 2Cr$
$\Delta H=\Sigma \Delta_f H^{\circ}_{products}$ $-\Sigma \Delta_1 H^{\circ}_{recectants}$
$=\left|\Delta_r H^{\circ} _{ Al _2 O _3}+2 \Delta_f H _{ Cr }^{}\right|-\left[2 \Delta_1 H _{ Al }^0+\Delta_1 H _{ Cr _2 O_3}^0 \mid\right.$
$=\mid-1596+2(0)]-|2(0)+(-1134)|$
$=-462\, kJ$
$(I)$ ${H_2}(g) + \frac{1}{2}{O_2}(g) \to {H_2}O(l);$
$\Delta {H^o_{298\,K}} = - 285.9\,kJ\,mo{l^{ - 1}}$
$(II)$ ${H_2}(g) + \frac{1}{2}{O_2}(g) \to {H_2}O(g);$
$\Delta {H^o_{298\,K}} = - 241.8\,kJ\,mo{l^{ - 1}}$
તો પાણીની મોલર બાષ્પાયન એન્થાલ્પી .....$kJ\,mol^{-1}$
$N \equiv N\,\left( {946\,kJ\,mo{l^{ - 1}}} \right)\,;\,N = N\,\left( {418\,kJ\,mo{l^{ - 1}}} \right)$
$O = O\,\left( {498\,kJ\,mo{l^{ - 1}}} \right)\,;\,N = O\,\left( {607\,kJ\,mo{l^{ - 1}}} \right)$;