Matriculation Chemistry Reaction Kinetics part 4.pdf

8/12/2019 Matriculation Chemistry Reaction Kinetics part 4.pdf

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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)

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Matriculation Chemistry Reaction Kinetics part 4.pdf