Chemical reaction engineering is that engineering activity which is concerned with the exploitation of chemical reactions on commercial scale. The areas of different fields of science like: Oil Refining Pharmaceuticals Biotechnology Chemical Industries Sustainable Development

1. Chemical Reaction
Engineering

2. Definition
Chemical reaction engineering is that
engineering activity which is
concerned with the exploitation of
chemical reactions on commercial
scale.
Octave Levenspiel “chemical reaction
engineering”

3. CRE Covers
The areas of different fields of science like:
Oil Refining
Pharmaceuticals
Biotechnology
Chemical Industries
Sustainable Development

5. CRE is the discipline that quantifies
the interactions of transport
phenomena (Heat, Mass and flow) and
reaction kinetics in relating reactor
performance to operating conditions
and feed variables.

6. Rate Equation
The rate law or rate equation for a chemical
reaction is an equation that links the reaction
rate with the concentrations or pressures of the
reactants and constant parameters (normally
rate coefficients and partial reaction orders).
For many reactions the rate is given by a power
law.

7. Rate Equations (or Rate Laws)
7
Consider:
A + B = C + D (1)
 Consider molecules in a reaction system
◦ The more reactant molecules in the system, the more chance for reactant molecules to
meet - the more effective collision between these molecules, which lead to reaction to
occur, thus:
rate [A][B] (2a)
Reactant A molecules may differ from B molecules in leading to reaction, this may be
written as:
rate [A]a[B]b (2b)
◦ If a reaction approaches equilibrium conversion, the more product molecules in the
system, the more chance for product molecules to meet - causing the reverse reaction,
thus:
reverse rate [C][D] or rate [C][D] = [C]-[D]- (3)

8. Rate Equations (or Rate Laws)
8
 Considering the effectiveness of product C and D molecules in
causing the reverse reaction, we have:
rate [C]l[D]d
 Reaction rate, ri, in relation to reactant/product i, in general
form:
where k is reaction rate constant
dlba
[D][C][B][A]k
][

dt
id
ri

9. Rate Equations
9
 Different appearances of rate equation
For a reaction vAA + vBB = vCC + vDD (1)
 If reaction is far away from equilibrium conversion, the reverse reaction is negligible,
 If reactant A in large excess, which means that the conc. of A can be considered as
constant,
 Some reactions do not depend on the concentration of neither reactant nor product,
 There exist other more complicated forms of rate equations.
ba
[B][A]
][
k
dt
id
ri 
k
dt
id
ri 
][
  bba
[B][B][A]
][
'kk
dt
id
ri 

10. Rate Constant
The constant k is the reaction rate
constant or rate coefficient of the
reaction. The value of this
coefficient k may depend on conditions
such as temperature, ionic strength,
surface area of an absorbent, or light
radiation.

11. Elementary Reactions

12. Elementary Reactions
An elementary reaction is a chemical reaction in
which one or more chemical specie react
directly to form products in a single reaction
step and with a single transition state.

13. Example on Board

14. These Reactions May be
• Unimolecular
In which a molecule dissociates or isomerizes.
• Bimolecular
In which addition or substitution occurs.

15. Law of Mass Action
The law of mass action is the proposition that
the rate of a chemical reaction is directly
proportional to the product of
the activities or concentrations
of the reactants.

16. Bimolecular Reactions
The rate expression for an elementary
bimolecular reaction is sometimes referred to as
the Law of Mass Action as it was first proposed
by Guldberg and Waage in 1864.
An example of this type of reaction is
a cycloaddition reaction.

17. Representation of an Elementary
Reaction
2A 2R
A R
k1
-rA = rR = k1C2
A
k1
-rA = rR = k1CA
17

18. Why this Classification
Necessary

19. 19

20. Non-Elementary Reactions

21. Non-Elementary Reaction
The reactions in which formation of product
from the original reactants occur through a
series of steps are called as non- elementary
reactions

22. • For non-elementary reactions there is difference
between order and stoichiometric coefficient .
• We observe Non-Elementary reaction as a single
reaction rather than elementary reactions in series
because the amount of the intermediates formed is
negligibly small and cannot be detected

23. Types of Intermediates
1. Free Radicals
Free atoms or larger fragments of stable
molecules that contain one or more unpaired
electrons are called free radicals.
They are highly reactive and un stable
Examples:
CH3 C2H5 I. H.

24. Ions and Polar substances
Electrically charged Atoms and Molecules
N3-,Na+, OH- I-
Are called ions these may act as active
intermediates in reactions

25. Molecules
Consider the consecutive reactions
A R S
These are multiple reactions .
however, if the intermediate R is highly reactive
its life time will be very small to measure. In
such situation R may not be observed and can
be consider to be a reactive intermediate.

27. Difference between elementary and
non- elementary reactions
•Elementary reactions are single step
reactions whereas non elementary
reactions are multistep reactions , i.e , such
reactions occur through a series of reaction
steps.
•Elementary reactions are simple in nature
whereas the non elementary reactions are
complex in nature

28. • For elementary reactions the order agrees with the
stoichiometry whereas for non elementary reaction
,the order does not agrees with the stoichiometry
• (i.e., there is a difference between order and
stoichiometric coefficient)
•For an elementary reaction, the order of reaction
must be an integer whereas for a non elementary
reaction, the order of reaction may be an integer or
have a fractional value

30. Chain Reaction And Non Chain
Reaction

31. Chain Reaction:
• A chain reaction is a sequence of reactions
where a reactive product or by-product causes
additional reactions to take place.

32. • If two molecules react, not only molecules of
the final reaction products are formed, but also
some unstable molecules which can further
react with the parent molecules with a far
larger probability than the initial reactants
• In the new reaction, further unstable molecules
are formed besides the stable products, and so
on ..

33. Typical types:
• The main types of steps in chain reaction are of the
following types
 Initiation (formation of active particles and free
radicals formed)
 Propagation (several elementary steps in a cycle,
where the active particle through reaction forms
another active particle which continues chai)
 Termination (elementary step in which the active
particle loses its activity; by recombination of two free
radicals)

35. Non-Chain Reaction:
• A reaction that is in single step reaction.
A *R S
2NaoH + Cl2 2NaCl + HCl
+ H20

36. Thank You For
Patience Listening