Ethanol has a molecular formula of C2H5OH. When ethanol undergoes combustion the carbon atoms combine with oxygen to produce carbon dioxide or CO2 and the hydrogen atoms combine with oxygen to produce water or H2O.
C2H5OH (l) + 3 O2 (g) --> 2 CO2 (g) + 3 H2O (g)
The combustion of ethanol is an exothermic reaction and the energy produced during the combustion of 1 mole of ethanol is 1371 kJ.
The value of the heat released when one mole of ethanol is burned has to be determined by an independent experiment where ethanol is burned and the heat released is measured. It cannot be derived by adding the values of heat released during the combustion of individual carbon atoms and individual hydrogen atoms as the formation of ethanol itself releases some heat.