Limiting reagent or reactant

Category : JEE Main & Advanced

Limiting reagent or reactant

         In many situations, an excess of one or more substance is available for chemical reaction. Some of these excess substances will therefore be left over when the reaction is complete; the reaction stops immediately as soon as one of the reactant is totally consumed.

           The substance that is totally consumed in a reaction is called limiting reagent because it determines or limits the amount of product. The other reactant present in excess are called as excess reagents.

           Let us consider a chemical reaction which is initiated by passing a spark through a reaction vessel containing 10 mole of H2 and 7 mole of O2.

                                      \[2\underset{{}}{\mathop{\,{{H}_{2}}\,}}\,(g)\,\,+\,\,\underset{{}}{\mathop{{{O}_{2}}\,}}\,(g)\,\xrightarrow{{}}\,\,2\,\,\underset{{}}{\mathop{{{H}_{2}}O}}\,\,(v)\]

Moles before reaction

10

7

0

Moles after reaction

0

2

10

           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.



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