Do you know!

You can easily find excess and limiting reactants

Firstly, you must know that !!

What is Limiting reactant and excess reactant?

Limiting Reactant Definition:

The reactant which is used up completely and earlier in a chemical reaction is called a limiting reactant.

Limiting reactant is also known as limiting reagent .

Excess Reactant Definition:

The reagent / reactant which left behind after the completion of a chemical reaction is called excess reactant or excess reagent.

Super Simple Trick to identify Limiting & Excess Reagent:

1. Calculate the number of moles of each reactant.

2.Then calculate the total number of moles for each reactant using balanced chemical equation.

3. The reactant /reagent that gives the least amount of product is the limiting reactant & the reactant /reagent that gives the greater amount of product is the excess reactant.

Limiting reagent and Excess Reagent Example:

Let 1 mole of H₂ & 1 mole of O₂ be reacted to produce H20. The limiting and excess reagent can be determined as:

Solution:

Balanced Chemical equation is as follow:

Given:

Unbalance Chemical Equation

i) 2 moles of H₂ = 2 moles of H₂O

1 moles of H₂ = 1 x 2 moles of H₂O = 1 moles of H₂O

2

ii) 1 moles of H₂ = 2 moles of H₂O

Since H₂ produces the least amount of product, therefore, it is a limiting reagent whereas O₂ produces greater amount of product therefore , O₂ is an excess reagent.

Determination of Excess reactant ( reagent ) consumed and un-used ( leftover) in a Chemical reaction:

O ₂ consumed in a chemical reaction can be easily determined by the comparison balanced and given chemical reactions.

2 mol H₂ needs  =  1 mol O ₂ ( Balance chemical reaction)

 1 mol H₂ needs  =    1  X  1    

                                       2

 1 mol H₂ needs   =0.5 mol O ₂

Since 0.5 moles of O₂ react with 1 mole of H₂ to produce H₂O .

How do you find the excess reactant left over in a reaction?

Un-used ( left over) Excess reagent in a Chemical reaction:

Left over (unused) reactant = total excess reagent- amount used

 Left over  O₂     =     1 mol        –      0.5 mol

                                                                          = 0.5 mol

Remember !!!

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Related Important Questions:

-> How does a limiting reagent control the amount of product formed?

When the limiting reagent is used up completely, the reaction stops and no more product will form.

The amount of product is always calculated on the basis of limiting reactant (reagent).

Limiting reactant always gives the least amount of product formation. Therefore, it controls the overall yield ( amount of product) of a chemical reaction.

Simply, the maximum amount of product formation ( yield ) depends on the amount of limiting reactant.

-> What is a Limiting reagent?

The reactant which is earlier consumed in a reaction or  The reactant which is completely consumed in a reaction to produce the product when the reaction is over” is called a limiting reactant.

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