$(i)$ : $C_6H_{6(l)} + \frac{15}{2} O_{2(g)}$ $→$ $6CO_{2(g)} + 3H_2O_{(l)}$

$\Delta H$ = $-783\,K\,cal$ 

$(ii)$ : $C_{(s)} + O_{2(g)}$ $→$ $CO_{2(g)}$

$\Delta H$ = $-97\,K\,cal$

$(iii)$ : $H_{2(g)} + \frac{1}{2} O_{2(g)}$ $→$ $H_2O_{(g)}$

$\Delta H$ = $-68\,K\,cal$

જેથી,

$6CO_{2(g)} + 3H_2O_{(l)}$  $→$ $C_6H_{6(l)} +  \frac{15}{2} O_{2(g)}$

$\Delta H$ = $+783\,K\,cal$

$6C_{(s)} + 6O_{2(g)}$ $→$ $6CO_{2(g)}$

$\Delta H$ = $-582\,K\,cal$

$3H_{2(g)} + \frac{3}{2} O_{2(g)}$ $→$ $3H_2O_{(g)}$

$\Delta H$ = $-204\,K\,cal$

ઉમેરવાથી,

$6C_{(s)} + 3H_{2(g)}$ $→$ $C_6H_{6(l)}$

$\Delta H = -3\,K\,cal$