Calculate enthalpy of combustion of  1 mole of octane C₈H_18(l)  using the following data:

 Given $∆{\mathrm{H}}_{\mathrm{f}}^0$  for CO_2(g), H₂O_(g) and C₈H_18(l) respectively are -390, -240 and +160 KJ/mol

C₈H_18(l) + $\frac{25}{2}$O_2(g)$\to$8CO_2(g) + 9 H₂O_(l)

$∆$H_c = [8$∆$f(CO₂) + 9$∆$Hf (H₂O)] - [$∆{\mathrm{H}}_{\mathrm{f}\left({\mathrm{c}}_8{\mathrm{H}}_{18}\right)}$ + $\frac{25}{2}$O_2(g)]

= - 3120 - 2160 - 160 = - 5440kJ/mole

when 1 mole is burnt energy released = 5440KJ=5.44Mj