matriculation chemistry reaction kinetics part 4.pdf
TRANSCRIPT
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11.2 Collision Theory
At the end of the lesson the students should be
able to:1. explain reaction rates in terms of collision
theory.
2. identify factors affecting the effectiveness of
collision.
3. define activation energy.
4. efine and state the characteristics of an
activated complex
!b"ectives
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# Collision Theory is the theory to explain the rate of
chemical reactions. $t is based on%
1& molecule must collide to react 2& molecules must possess a certain minimum 'inetic energy
(activation energy) to initiate the chemical reaction.
Collision Theory
*ate +umber of effective collisions
time
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# 3& molecule must collide in the right orientation in order
for the reaction to occur.
# !nly effective collisions cause formation of product%collisions of molecules ,ith -
aand at correct orientation.
# The activation energy (Ea) is the minimum energy that
must be supplied or reuired by collisions for a reaction tooccur.
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/..is the minimumenergy is required
to initiate the
chemical reaction.
The activation energy(Ea)
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$mportance of !rientation
Orientationis unimportant Orientationis important
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$mportance of !rientation
Orientationis important
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Transition 0tate Theory
# The configuration of the atoms of the
colliding species at the time of the collision is
called the transition state.
# 0pecies formed at transition state is called
activated complex.
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# ery unstable i.e. $t has a short half&life.
# $ts potential energy is greater than reactants or
products.
# The activated complex and the reactants are in
chemical euilibrium.
# $t decomposes to form products or reactants.
Characteristics of Activated Complex
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*eactant
product
& A reaction profile sho,s
potential energy plotted as afunction of the progress of the
reaction.
& The difference in potential
energies bet,een the
products and the reactants is& for the reaction.
& *eactant molecules must
have enough energy to
overcome an energy barrierseparating products from
reactants -a.
-a
rogress of reaction
otential energy
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A *eaction rofile: exothermic reaction
-a
-a(reverse reaction)
Activated complex
Transition state
(5or,ard reaction)
CO(g)+ NO2(g) CO
2(g)+ NO(g)
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Product
Reactant
activated complex.
Ea
(reverse reaction)
Ea
(forward reaction)
A *eaction rofile for endothermic process
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A *eaction profile: endothermic reaction
-a
2+!Cl 6 2+! 7 Cl2
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-xample:
1. 5or the reaction A 7 8 C 7 the enthalphy change ofthe for,ard reaction is 7 21 '9mol. The activation energy ofthe for,ard reaction is ;4 '9mol.
a)