If the heat of reaction is written on the reactant side of a chemical equation, what does that indicate about the reaction?
It means that the reaction is
Combustion reactions are of course
Such a reaction possibly cooked your dinner. And certainly we could treat the energy OUTPUT quantitatively according to the reaction stoichiometry.
On the other hand, we could treat an endothermic reaction similary...and here we represent the BOILING of water, a physical reaction...
And again this process could be addressed quantitatively. Capisce?