Here we're going to say that the heat of combustion is the amount of heat released when a mole of a substance is burned or combusted. Now recall, a combustion reaction normally involves a compound with carbon and hydrogen or carbon, hydrogen and oxygen reacting with O2.
Of course there are other elements that could be involved, such as sulfur or nitrogen, but the most common types of combustion reactions are just carbon and hydrogen or carbon, hydrogen and oxygen. Now we're going to say associated with any combustion reaction is a heat of combustion value, which we represent as ΔH⁰ so that little circle combustion.
So we'll abbreviate it as comb. So just remember when discussing constant volume calorimetry, we associated with a combustion reaction.