CONCEPT OF LIMITING REAGENTS:

The reagent which is consumed completely in the reaction and decides the amount of product is known as limiting reagent and left over reagent is known as excess reagent.
HOW TO FIND LIMITING REAGENT:
(1) Divide  the given moles of each reagent by its Stoichiometric coefficient.
(2) The reagent for which the division comes out minimum is called Limiting reagent.
SIGNIFICANT OF LIMITING REAGENT:
(1) The amount of product is decided by Limiting reagent .
(2) Amount of excess reagent left over and participate in the reaction is decided by Limiting reagent.
GENERAL ILLUSTRATION:

ILLUSTRATIVE EXAMPLE (1) : The Chemical reaction 

8 moles of P and 5 moles of Q will produce how many moles of  R ?

SOLUTION:

ILLUSTRATIVE EXAMPLE (2): The Chemical reaction
Carried out by taking 24 gm of Carbon (2 moles ) and 96 gm (3 moles ) of oxygen (O₂) find 

(1) Limiting reagent
(2) How many moles of CO formed
(3) percentage (%) of  reagent left over .

SOLUTION:

ILLUSTRATIVE EXAMPLE (3): 10 gm each of Lithium and Oxygen react to produce Li2O find out?
(1) Find the limiting reagent
(2) Mass of Li2O produced in reaction
(3) % of excess reagent consumed
(4) % of excess reagent undergoes in reaction.

SOLUTION:

ILLUSTRATIVE EXAMPLE (4): Equal mass of Zn (65) and S (32) reacts to form ZnS, Calculate fraction of excess reagent left unreacted.

SOLUTION:

ILLUSTRATIVE EXAMPLE (5):

Above reaction is carried out by taking 6 moles of each X and Y respectively then find % excess reagent react.

SOLUTION: Answer Key 25% unreacted  and 75% reacted