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Tuesday, 24 March 2015

FSc Notes Chemistry Molar Volume Stiochimetry Limiting Reactant Yield

FSc Notes Chemistry Molar Volume Stiochimetry Limiting Reactant

Molar Volume: 

One mole of any gas at standard temperature and pressure occupies 22.4114 dm3, which is called molar volume. for exp:
2.016 g of H2 = 1 mole of H2 = 6.02 * 10(23) mole of H2  =  22.414 dm3 of H2 at STP.
16 g of CH4 =  1 mole of CH4 = 6.02 * 10(23) mole of CH4  =  22.414 dm3 of CH4 at STP.
22.414 dm3 of each gas has a different mass but the same number of molecules. The reason is masses and the sizes of the molecules don't affect the volumes. It is known as in the gaseous state the distance between molecules is 300 times greater than their diameter.

Law of Conservation of Mass: 

Mass can neither be created nor destroyed in a chemical reaction. As matter is atomic in nature, so we can also state that: Atoms can neither be created nor destroyed in a chemical reaction.

Law of Definite Proportions: 

The different samples of same compound will contain the number of atoms of different elements in the same fixed ratio by mass.

Stiochiometry: 

The branch of chemistry which deals with the quantitative relationship between reactants and products in a balanced chemical equation is called Stiochiometry.
Assumptions when stiochiometric calculation are performed:
Chemical equation do not tell about the condition and the rate of reaction. Chemical equation can even be written to describe a chemical change that do not occur. So when these calculation are performed we have to assume the following conditions:
  • All reactants are completely converted into the products.
  • No side reactions occurs.
  • While doing calculation, law of conservation of mass and law of definite proportions are obeyed.

Stiochiometric Amounts: 

The amounts of reactants and products in a balanced chemical equations are called Stiochiometric amounts.

Mass-mass relationship: If we are given the mass of the one substance, we can calculate the mass of the other substance.
Mass-mole relationship or mole-mass relationship: If we are given the mass one substance, we can calculate the moles of the other substance and vice versa.
Mass-volume relationship: If we are given the mass of one substance, we can calculate the volume of the other substance and vice versa.

Limiting Reactant: 

The reactant which is consumed earlier during a chemical reaction and gives the least moles of the product is called limiting reactant.

Identification of Limiting Reactant: 

To identify limiting reactant in a chemical reaction following steps are performed:
  • Calculate the number of moles from the given amount of reactant.
  • Find out the number of moles of product with the help of a balanced chemical equation.
  • Identify the reactant which produces the least amount of product as limiting reactant.

Yield: 

The amount of product obtained as a result of chemical reaction is called yield.


Theoretical Yield: 

The amount of product calculated from balanced chemical equation, is called theoretical yield.

Actual Yield: 

The amount of product that is actually obtained experimentally in a chemical reaction is called actual yield.

Why Actual yield is less than Theoretical yield:
Chemical reactions do not produce the amount of products expected theoretically. The reason are:
  • Side reaction produces by products.
  • Reactions are reversible.
  • Mechanical loss of product during separation by filtration, separation by distillation, separation by a separating funnel, washing, drying and crystallization is not properly carried out decrease the yield.

Percent Yield or Efficiency of Reaction: 

Actual Yield divided by the theoretical yield and answer is multiplied by 100 is called percent yield.

Efficiency of Reaction = % yield = (Actual yield / Theoretical yield ) * 100

Written By: Asad Hussain

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