Mr. AzizullahFazaia Degree college, Peshawar

To teach the students the chemical processes which takes place in the presence of a catalyst.

The teacher will enlight the industrial and biological importance of catalysis. In industries greater yield is required in lesser time and low cost, it can be achieved by increasing the rate of a reaction and for this purpose activation energy of reacting species must be decreased , that’s why in industry and in synthetic reactions catalysts are frequently used.

The teacher will ask few questions from students.

Q. Why hydrogen and nitrogen do not react in air to form ammonia in atmosphere?A.Due to high activation energy

Q. Do all chemical reactions proceed through same kinetics?A.No

Q. Q. Define rate of a reaction?

The students have knowledge about the activation energy, Arrhenius equation, rate of reaction, chemical equilibrium and chemical kinetics.

Core Concept:

CATALYSIS

DLO 1:The students will be able to understand the concept of Catalysis, Catalyst and characteristics of catalyst.

BERZELIUS in 1935 for the first time used the term Catalysis and said that“The processes which takes place in the presence of a catalyst are known as catalysis.”

Then teacher will define Catalyst as.“A substance which alters the rate of a chemical reaction but remains unchanged at the end of a reaction.”

EXAMPLES OF CATALYSTS Ni, Pt hydrogenation reactions

Fe Haber’s ProcessRh, Pd catalytic

converters

Then the teacher will explain that

The Catalysts work by providing…

“An alternative reaction pathway which has a lower activation energy”

Board Summary

1. Catalysts offer alternative path for reaction.

Activity. Pouring oil on fire.

Then teacher will explain on the basis of activity that;

•A catalyst is a substance that changes the speed of a reaction without undergoing a permanent chemical change itself in the process.

•As a general rule, a catalyst is a substance that lowers the overall activation energy for a chemical reaction.

Board Summary

1. Catalysts offer alternative path for reaction.

2. They can not initiate a chemical reaction.

DLO 2:The students will be able to differentiate and among different types of Catalysis.

The teacher will enlist different types of catalysis.1. Heterogeneous catalysis2. Homogeneous catalysis3. Enzyme catalysis4. Autocatalysis…..

The teacher will ask about difference between these types of catalysis. The answer is expected from very few students , here teacher will explain each type in detail.

Students will be briefed that in this type,Catalysts are in a different phase to the reactantse.g. a solid catalyst in a gaseous reaction

Catalysis is thought to work in three stages...

AdsorptionAdsorption

ReactionReaction

DesorptionDesorption

1. Heterogeneous Catalysis

The teacher will explain the mechanism of the Heterogeneous catalysis with the help of a modelAdsorption (STEP 1)Reaction (STEPS 2 and 3)Desorption (STEP 4)

2. Homogeneous Catalysis

The teacher will explain that

• catalyst and reactants are in the same phase

• reaction proceeds through an intermediate species

of lower energy

• there are usually more than one reaction step

Example

Acids Esterificaton

Conc. H2SO4 catalyses the reaction between acids and alcohols

Important note:

Catalysts have NO EFFECT ON THE POSITION OF EQUILIBRIM but they do affect the rate at which equilibrium is reached

Board Summary

1. Catalysts offer alternative path for reaction.

2. They can not initiate a chemical reaction.

3. They are recovered at the end of reaction.

Auto-catalysisAuto-catalysis

Occurs when a product of the reaction catalyses the reaction itself

It is found in the reactions of Manganate(VII) with Ethanoxalate.

Enzyme Activity is affected by ...

1. Temperature

2. Substrate concentration

3. pH

4. Being poisoned

3. ENZYME Catalysis3. ENZYME Catalysisenzymes are biologically active homogeneous catalysts, functions through

“lock and key” mechanism, resulting High specificity.

Board Summary

1. Catalysts offer alternative path for reaction.

2. They can not initiate a chemical reaction.

3. They are recovered at the end of reaction.

4. Catalyts may be in same or in different phases w.r.t to reactants.

5. Some products can act as autocatalysts.

Inhibitors and poisonsInhibitors and poisons

The teacher will explain that catalytic reactions can be stopped at any point by adding certain chemicals called inhibitors. Or Impurities in a reaction mixture can also adsorb onto the surface of a catalyst decreasing efficiency, causing poisoning of catalyst.

examples Sulphur Haber’s processLead catalytic converters in cars

Board Summary

1. Catalysts offer alternative path for reaction.

2. They can not initiate a chemical reaction.

3. They are recovered at the end of reaction.

4. Catalyts may be in same or in different phases w.r.t to reactants.

5. Some products can act as autocatalysts.6. Catalysts may be poisoned.

We have discussed the mechanism and action of catalyst, homogeneous catalysis, heterogeneous and enzyme catalysis. We also discussed auto catalysis and poisoning of catalyst

The teacher will invite the students to ask questions.

Teacher will ask the following questions to ensure that the concepts are being conveyed to the students.

Q. What is a catalyst?

Q. In synthesis of ammonia which catalyst is used?

Q. What are main steps in mechanism of heterogeneous catalysis?

Q. Can a catalyst initiate a chemical reaction?

Q. Do catalyst alter the equilibrium of a reaction?

Q. What is difference between homogeneous and heterogeneous catalysis?

The teacher will assign homework which is to be submitted on 20th May , 2010.

1.Write down the mechanism of heterogeneous catalysis with few examples.

2.Explain key and lock mechanism of Enzyme catalysis.

In this lesson we have discussed that what are catalysts and how they take part in chemical reactions and how many types of catalysis are there,depending on the chemical and physical nature of a catalyst.

In next class we will discuss the activation of catalyst and enzyme action of catalysts.

THANK YOU