Kinetics of Organic Chain Reactions.pptx

Advance Chemical Kinetics, Material analysis, Physical Chemistry

1. SUPERIOR UNIVERSITY LAHORE, FAISALABAD CAMPUS Department of Chemistry 1

2. ﷽ اللہ کے نام سے شروع، جو بڑا مہربان نہایت رحم والا ہے۔ BIGGER . BOLDER. SUPERIOR 2

3. SUPERIOR UNIVERSITY LAHORE, FAISALABAD CAMPUS Welcome to the Presentation 3

4. 4 ADVANCED CHEMICAL KINETICS Kinetics of Organic Chain Reactions Presented By: MUHAMMAD ARSLAN ABID Roll # SU74-MSCHW-SA24-011 Semester # 01 Instructor: Dr. IMRAN MALHI

5. 5 Kinetics of Organic Chain Reactions CONTENTS

6. 6 Kinetics of Organic Chain Reactions Introduction What are Organic Chain Reactions? Reactions whose mechanism includes one or more steps that are repeated indefinitely, until the chain is terminated and reactants are used up. A process in which reaction components undergo multiple reactions until an endpoint occurs is called a chain reaction . Organic chain reactions are a type of complex reaction involving a series of steps that lead to the formation and consumption of reactive intermediates. These reactions are prevalent in polymerization processes and in the degradation of organic compounds. A reaction mechanism is a step-by-step sequence of elementary reactions by which overall chemical change occurs. Each step is called an elementary reaction , and the sequence of these steps constitutes the reaction mechanism .

7. 7 Kinetics of Organic Chain Reactions Mechanism Mechanism of Organic Chain Reactions Chain reactions proceed through three main steps: Initiation : The formation of reactive intermediates such as free radicals or ions. Propagation : The intermediates react with stable molecules to form new intermediates and products. Termination : The reactive intermediates combine to form stable products , ending the chain reaction.

8. 8 Kinetics of Organic Chain Reactions Mechanism Mechanism of Organic Chain Reactions Step # 1 Initiation : In the initiation step, reactive intermediates are generated. For example, the homolytic cleavage of a chlorine molecule under UV light produces chlorine radicals : Cl 2 Cl + Cl  

9. 9 Kinetics of Organic Chain Reactions Mechanism Mechanism of Organic Chain Reactions Step # 2 Propagation: During propagation, the reactive intermediates react with stable molecules to produce new intermediates and products. For example, in the chlorination of methane Cl +CH 4 HCl+CH 3 CH 3 + Cl 2 CH 3 Cl+ Cl  

10. 10 Kinetics of Organic Chain Reactions Mechanism Mechanism of Organic Chain Reactions Step # 3 Termination: Termination occurs when two reactive intermediates combine to form a stable product, effectively ending the chain reaction. Cl + Cl Cl 2 Cl +CH 3 CH 3 Cl  

11. 11 Kinetics of Organic Chain Reactions Characteristics Characteristics of Chain Reactions The probability factor P of chain reactions is generally greater than unity The chain reactions, sometimes possess excessive speeds which may lead to explosion The chain reactions begin at zero rate and then rises to maximum and then falls of with time shown in the diagram.

12. 12 Kinetics of Organic Chain Reactions Characteristics Characteristics of Chain Reactions iv ) As the chain reaction begin at zero rate , it therefore requires enough time so that the rate of the reaction could be detected experimentally. v) The speed of the chain reactions is retarded or accelerated by traces of other substances. vi) The rate of chain reactions is influenced by the changes in shape of the containing vessel . vii)The chain reactions are rarely of simple orders but have integral orders which depends upon the vessel shape and other experimental conditions .

13. 13 Kinetics of Organic Chain Reactions Kinetics Analysis Steady State Approximation The steady-state approximation assumes that the concentration of reactive intermediates remains constant throughout the reaction. This simplification allows us to derive the overall rate law. For a generic chain reaction, the rate laws for each step can be written as: Initiation: A R 2. Propagation: R + B [ Kp ]P+R 3. Termination: R+R   Rate of Organic Chain Reactions The rate of chain reactions is determined by the rates of the initiation, propagation , and termination steps. The overall rate can be complex due to the involvement of multiple steps.

14. 14 Kinetics of Organic Chain Reactions Kinetics Analysis Steady State Approximation for the Reactive intermediate (R) Steady state approximation states that the rate of formation of reactive intermediate is equal t o the rate of disappearance of reactive intermediate in the chain reactions i.e., the rate of formation of intermediate (R) and the rate of disappearance of intermediate (R) must be equal to zero =  

15. 15 Kinetics of Organic Chain Reactions Kinetics Analysis Steady State Approximation for the Reactive intermediate (R)

16. 16 Kinetics of Organic Chain Reactions Kinetics Analysis Steady State Approximation for the Reactive intermediate (R)

17. 17 Kinetics of Organic Chain Reactions Kinetics Analysis Steady State Approximation for the Reactive intermediate (R)

18. 18 Kinetics of Organic Chain Reactions Examples Polymerization Reactions Chain polymerization involves the growth of polymer chains through the successive addition of monomer units. An example is the polymerization of ethylene to form polyethylene :

19. 19 Kinetics of Organic Chain Reactions Examples Combustion Reactions The combustion of hydrocarbons involves a series of chain reactions that lead to the formation of carbon dioxide and water. For example, the combustion of methane can be represented as:

20. 20 Kinetics of Organic Chain Reactions Examples Halogenation Reactions Halogenation of alkanes is another example of a chain reaction. For instance, the chlorination of methane:

21. 21 Kinetics of Organic Chain Reactions Case Study Polymerization of Styrene The polymerization of styrene is a well-known example of a chain-growth polymerization. The process involves: Initiation: Formation of free radicals, often by thermal decomposition of a radical initiator . Propagation: Propagation: The growing polymer radical adds monomer units. Termination: Termination: Two growing polymer radicals combine.

22. 22 Kinetics of Organic Chain Reactions Conclusion Understanding the kinetics of organic chain reactions is crucial for controlling and optimizing industrial processes, such as polymer production and combustion. The study of these reactions provides insights into the detailed mechanisms and allows for the development of better catalysts and reaction conditions. Advances in this field contribute significantly to materials science, environmental applications, and energy production .

23. 23 Kinetics of Organic Chain Reactions References P . Atkins and J. de Paula, Atkins’ Physical Chemistry, 10th Edition, Oxford University Press, 2014. M . B. Smith and J. March, March’s Advanced Organic Chemistry: Reactions , Mechanisms, and Structure, 7th Edition, Wiley, 2013. J . E. House, Principles of Chemical Kinetics, 2nd Edition, Academic Press, 2007. L . D. Schmidt, The Engineering of Chemical Reactions, 2nd Edition, Oxford University Press, 2004. S . Carra , G. Fornasari , Catalytic Kinetics, Elsevier, 2010.

24. 24 Kinetics of Organic Chain Reactions

25. 25 ADVANCED CHEMICAL KINETICS Kinetics of Organic Chain Reactions Presented By: MUHAMMAD ARSLAN ABID Roll # SU74-MSCHW-SA24-011 Semester # 01 Instructor: Dr. IMRAN MALHI