$31)$

$C_3H_8(g)+5O_2(g) \xrightarrow{t^o} 3CO_2(g)+4H_2O(g)$

$\rm \Delta _r H^o_{298}$

$\rm= 2 \times 346+8 \times 418 +5 \times 494-3 \times 2 \times 732-4 \times 2 \times 459 $

$\rm =(-1558 )(kJ)$

$C_4H_{10}(g)+\dfrac{13}{2}O_2(g) \xrightarrow{t^o} 4CO_2(g)+5H_2O(g)$

$\rm \Delta _r H^o_{298}$

$\rm=3 \times 346+10 \times 418 +5 \times 494-4 \times 2 \times 732-5 \times 2 \times 459 $

$\rm =(-2758 )(kJ)$

$1(mol)$ $gas$ ứng $n_{C_3H_8}=0.4(mol) ;n_{C_4H_{10}}=0.6(mol)$

`->`$\Delta _r H^o_{298}=0.4 \times (-1558)+0.6 \times  (-2758)=(-2278)(kJ/mol)$