# How do you work out the amount of energy which will be released when a substance undergoes combustion in a pure oxygen environment [closed]

For instance, if we have an abundance of pure Oxygen and one kilogram of Hydrogen and all the Hydrogen reacts with the Oxygen to form H20, how do you work out the amount of energy which will be released.

You can use basic stoichiometry. Look up the value of $\Delta H=-x \text{ kJmol}^{-1}$ for complete combustion of one mole of hydrogen.
$$\ce{H2(g)\+1/2O2(g)->H_2O(g)}$$
Calculate the number of moles ($n$) of hydrogen present in one kilogram.
Can you now calculate the total amount of energy released for combustion of $n$ moles of hydrogen?