Catalysis: Ncert class 12th chemistry Notes

catalysis Ncert class 10th/12th chemistry Notes

Introduction:

Term " Catalysis " was introduced as early as 1836 by Berzelius. A catalyst is a substance which alters, the reactants and the products are in the same phase are called Homogeneous catalysis. process in which the catalyst, the reactants and the products.

Content We Cover In catalysis

👉 Type of catalyst and catalysis

👉 Homogeneous and heterogeneous catalysis 

👉 Theory of Catalysis 

👉 Characteristics of catalyzed reactions

👉 Action of catalytic 

👉 Promoters and in inhibitors

 " Catalysis " Short Information:

The term " Catalysis " was introduced as early as 1836 by Berzelius in order to explain various decomposition and transformation reaction that includes Catalyst.

Definition of Catalysis:

A catalyst is a substance which alters (increases or decreases) the rate of a chemical reaction without itself undergoing any chemical change and the phenomenon is known as Catalysis.

Type of Catalysts:-

👉 There are two main types of catalysis

(a) Homogeneous catalysis

(b) Heterogeneous catalysis

(a) Homogeneous catalysis:-

The process in which the catalyst, the reactants and the products are in the same phase is called Homogeneous catalysis. This type of catalysis can occur in the gas phase or liquid (solution) phase.

 👉Example of Homogeneous catalysis in the gas phase

(a)Oxidation of sulphur dioxide to Sulphur trioxide with Nitric oxide as a catalyst.

2SO₂ + O₂ + No  →   2SO₃ + NO   

(b)Decomposition of Formaldehyde With Iodine as a catalyst.

CH₃CHO + I₂   →  CH₄ + CO  

👉 Example of Homogenius In solution phase(Liquid Phase)  

Many reactions in solutions are catalyzed by H^{+ and bases (}OH^-)

(a) Hydrolysis cane sugar in aqueous solution in the presence of Mineral Acid as Catalyst.

                                                 

^C₁₂H₂₂O_{11 +} H₂o + H₂SO₄ →   C₆H₁₂O₆ + C₆H₁₂O₆ + (H₂SO₄)

(b) Hydrolysis of an ester in the presence of Acid or Alkali 

CH₃COOC₂H₅ + H₂O + H⁺\OH^{-  →}     CH₃COOH + C₂H₅OH

(c)Decomposition of Hydrogen peroxide in the presence of Iodine ion as a catalyst

    

2H₂O₂ + I^{-        →}    2H₂O + O₂

(b) Heterogeneous catalysis:-

The process in which the catalyst, the reactant and the product are in a different phase is called Heterogeneous catalysis.

The most important reaction are those in which reactants are in the gas phase and the catalyst is solid.

(1) Heterogeneous catalysis with gaseous reactants  

(a) Combination of sulphur dioxide and the oxygen in the presence of finely divided platinum and Vanadium Pentaoxide      ₍V₂O₅).

2SO₂ + O₂ + Pt   →  2SO₃ +Pt

(b) Combination of Nitrogen to form Ammonium in the presence of finely divided iron

N₂ + 3H₂ + Fe   →     2NH₃ + Fe

(2) Heterogeneous catalysis with liquid reactants.

(a) The decomposition of an aqueous solution of hydrogen peroxide is catalyzed by manganese dioxide or platinum in colloidal form.

2H₂O₂ + Pt   →    2H₂o + o₂ + pt   

(b) Benzene and ethanol chloride react in the presence of anhydrous Aluminium chloride to form phenyl methane, Kenton. 

C₆H₆ + CH₃COCl + Alcl₃  →       C₆H₅COCH₃ + Hcl + AlCl₃

_{(3) Heterogeneous catalysis  with solid reactants} 

_{The decomposition of potassium chlorate is catalyzed by manganese dioxide.}

   2KClO₃ + MnO₂     →      2KCl + 3O₂ + MnO₂

Characteristics of catalyzed reactions:

👉 Some characteristics of the catalyzed reaction as follows:-

(1) The catalyst remains unchanged in mass and chemical composition at the end of the reaction:- 

It has been observed that a catalyst undergoes no change in mass and in chemical nature. However, it may undergo a physical change. 

Granular Manganese dioxide used in the decomposition potassium chlorate becomes finally powered at the end of the reaction.

(2) A small quantity of the catalyst is needed to carry out the reaction:-

(i) For example in the decomposition of hydrogen peroxide one gram of colloidal platinum can be catalyses  108 litres of hydrogen peroxide.

(ii) In Friday crafts reaction anhydrous aluminium chloride is required in a relatively larger amount to the extent of 30% of the mass.

(iii) For the acid and alkaline hydrolysis of an ester, the rate of reaction is proportional to the concentration of catalyst. 

Also Read: The solid-state class 12th imperfection of metals 

                                           

 

     

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