We are commonly asked to find the extra reactants in a chemical equation. We can find it after balancing the equation and seeing the amount of moles that are present for each substance.
Hence in chemistry and thermodynamic reactions it is the extra reactants that are not used up during the combustion process and therefore is excess of a said element.
There are also limiting reagent which is the substance that limits the amount that can react and can be produced in a chemical reaction
The limiting reagent in a chemical reaction is a reactant that is totally consumed when the chemical reaction is completed. The amount of product formed is limited by this reagent, since the reaction cannot continue without it.
why is excess reagent used:
A good way to ensure that one reactant fully reacts is to use an excess of the other reactant. This is financially efficient when one of the reactants is very cheap. When one reactant is in excess, there will always be some left over.
how do you find the excess reagent:
The reactant that produces a lesser amount of product is the limiting reagent. The reactant that produces a larger amount of product is the excess reagent. To find the amount of remaining excess reactant, subtract the mass of excess reagent consumed from the total mass of excess reagent given
