This presentation discusses chain reactions in chemical engineering kinetics. Chain reactions are self-sustaining reactions where the products initiate further reactions of the same type. They proceed in three stages: initiation, propagation, and termination. Initiation forms reactive intermediates through processes like heating or light absorption. Propagation involves these intermediates reacting with reactants to form more intermediates and stable products. Termination ends the chain when reactants are consumed or inhibitors are introduced. Examples are polymerization and nuclear fission reactions.

2. Presentation
“Chemical Engineering
kinetics”

3. Topic: Chain Reactions
Presented By:
Rahat Inayat Ali
14 CH 23
Presented To:
Prof. Dr. Abdul Rehman Memon

4. Introduction
Chain reaction is process yielding product that
initiate further process of the same kind, a self
sustaining sequence
OR
Reaction that results in a product necessary for
the continuation of the reaction.
Examples are :
• Polymerization of ethylene to polyethylene.
• Nuclear fission brought about by neutrons.

5. Explanation
• Chain reactions are in general very rapid but
are also highly sensitive to reaction conditions,
probably because the substances that sustain
the reaction are easily affected by substances
other than the reactants themselves.
• The chain length in a chain reaction is defined
as the number of propagation steps per
initiation step.

6. Three Stages Of Chain Reaction
1. Initiation
2. Propagation
3. Termination
1.Initiation, in which a reactive intermediate,
which may be an atom, an ion, or a neutral
molecular fragment, is formed, usually through
the action of an agent such as light, heat, or a
catalyst.
It can be This can be by thermolysis (heating) or
photolysis (absorption of light) leading to the
breakage of a bond.

7. 2.Propagation, whereby the intermediate reacts
with the original reactants, producing stable
products and another intermediate, whether of
the same or different kind; the new
intermediate reacts as before, so a repetitive
cycle begins.
3.Termination, which may be natural, as when all
the reactants have been consumed or the
containing vessel causes the chain carriers to
recombine as fast as they are formed, but
more often is induced intentionally by
introduction of substances called inhibitors or
antioxidants.

8. References
• http://chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/Kinetics/Rea
ction_Mechanisms/Chain_Reactions_I
• https://www.britannica.com/science/chain-reaction
• http://vallance.chem.ox.ac.uk/pdfs/KineticsLectureNotes.pdf
• http://www.dstuns.iitm.ac.in/teaching-and-
presentations/teaching/undergraduate%20courses/cy102-equilibrium-and-
dynamics-of-chemical-systems/lectures-2004/L18.pdf
• http://www.carborad.com/Volume%20I/Chapter%202/Chain%20Reactions.pdf