Answer
The energy released is 9.00 $\times 10^{6}$ J/kg.
Work Step by Step
In the reation, two oxygen atoms combine with one carbon atom and produce carbon dioxide.
Mass of Oxygen is 16 u & mass of Carbon is 12 u.
$\therefore$ Total initial mass is $2(16.0 \mathrm{u})+(12.0 \mathrm{u})=44$ u.
Converting the mass into kg units, we get,
$$
(44 \mathrm{u})\left(1.661 \times 10^{-27} \mathrm{kg} / \mathrm{u}\right)=7.31 \times 10^{-26} \mathrm{kg}
$$
Thus, 7.31 $\times 10^{-26}$kg of initial reactants was used. From previous question, we know the amount of energgy produced per carbon atom which can be also simplified as each combustion event produces $6.58 \times 10^{-19} \mathrm{J}$ so the energy produced per unit mass of reactants is $\left(6.58 \times 10^{-19} \mathrm{J}\right) /\left(7.31 \times 10^{-26} \mathrm{kg}\right)=9.00 \times 10^{6} \mathrm{J} / \mathrm{kg}$
