Limiting reagent

The limiting reagent (or limiting reactant) in a chemical reaction is the reactant that will first get exhausted, and which hence limits how far the reaction can go.

The limiting reagent is not something intrinsic to the reaction itself, but depends both on the equation of the reaction and on the quantities of the reagents present in the given chemical setup.

The notion of limiting reagent is typically useful for reactions that are irreversible, or where there is a severe barrier to the reverse reaction occurring. For reversible reaction, the notion of chemical equilibrium gives a more accurate picture.