A limiting reagent is a reactant which is present in lesser amount in a reaction. When it gets consumed, the reaction will not proceed irrespective of the amount of other reactant present in the reaction. It limits the amount of product formed. In other words, it determines the extent of reaction. Let us consider a chemical reaction which is initiated by passing a spark through a reaction vessel containing 10 moles of H2 and 7 moles of O2.
The reaction stops only after consumption of 5 moles of O2 as no further amount of H2 is left to react with unreacted O2. Thus H2 is a limiting reagent in this reaction.
