What is the quantity of a reactant that is more than enough to react with a limiting reagent?
Particularly in combustion reactions, the reagent in excess is dioxygen. We assume complete combustion, and dioxygen is assumed to be present in quantity:
This is balanced with respect to mass and charge, as indeed it must be if it purports to represent reality. The energy evolved from reaction may also be calculated quantitatively. Again, this is reasonable because we make a definite quantity of
In the internal combustion, and diesel engines (especially), this assumption of complete combustion is UNJUSTIFIED, and modern engines still produce quantities of the products of incomplete combustion,