# Why is a limiting reactant important in stoichiometry?

Jul 14, 2016

Because mass is conserved in every chemical reaction.

#### Explanation:

Stoichiometry requires that matter be conserved. So if I start with 20 g of reactant from all sources, at most I can isolate 20 g of product. In practice, I am not even going to get that.

Since atoms and molecules have definite and measurable mass, it follows that the mass of the products must equal the mass of the reactants. And thus we illustrate the principle of stoichiometry: $\text{garbage in must equal garbage out}$.

Clearly, a stoichiometrically balanced equation is necessary to assess which reagent is in excess, and which is in deficiency.

Want to hear something funny? The editor objects to the other word for $\text{donkey, i.e. what Balaam owned}$. It does not object to the very old English equivalent, $\text{arse}$. C'est la vie.