What is thermochemistry with equation stoichiometry?
Consider an exothermic combustion reaction. The amount of heat may be treated as a stoichiometric product, precisely dependent on the amount of hydrocarbon combusted.
Methane combustion drives our civilization to a very great degree:
The quoted enthalpy of combustion is per mole of reaction as written. You don't have to know these; you do have to know how to balance the equation. Because this energy is associated with the combustion of 1 mol of methane, I could also treat the evolved energy as a reagent or product in the reaction:
It would be on the reactant side if the reaction was endothermic. In other words the minus sign denotes evolution of heat. Alternatively,