Catalysis

Chemistry Lectures By Al-Chemist
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Reaction Rates How we measure rates.
Rate Laws
How the rate depends on amounts
of reactants.
Integrated Rate Laws
How to calc amount left or time to
reach a given amount.
Half-life
How long it takes to react 50% of
reactants.
Arrhenius Equation How rate constant changes with T.
Mechanisms
Link between rate and molecular
scale processes.
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Assumptions
 1- For a reaction to take place reactant
molecules must collide
 A B AB
 Collision of A and B
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The colliding molecules must collide with
proper orientation
 AB + CD ---- AC + BD
 A ----- C
 ----- A C + B D
 B ------ D
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 In order to make the collisions fruitful,the
colliding molecules must possess sufficeint
energy to collide otherwise the reaction will
not occur
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 Transition state theory (TST) describes a
hypothetical “transition state” that occurs in
the space between the reactants and the
products in a chemical reaction. The species
that is formed during the transition state is
known as the activated complex.
 AB + CD---- A ---- C --- AC+BD

 B----- D
 Activated Complex
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 The term Activation Energy was introduced in
1889 by Svante Arrhenius, a Swedish
scientist. It is defined as the least possible
amount of energy (minimum) which is
required to start a reaction or the amount
of energy available in a chemical system for a
reaction to take place.
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 Generally there is an inverse relationship
between Activation Energy and Temperature
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Svante Arrhenius developed a mathematical
relationship between k and Ea:
where A is the frequency factor, a number that
represents the likelihood that collisions would
occur with the proper orientation for reaction.

 A catalyst is defined as a substance which
when added to reacting system increases the
rate of the reaction without its self being
consumed in the reaction. Eg
 MnO2
 2KClO3 KCl+3O2

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 Two types
 Homogenous catalysis
 Heterogenous Catalysis
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 Homogeneous catalysis refers to reactions
where the catalyst is in the same phase as the
reactants, principally in solution.
 NO
 2SO2 + O2 2SO3
 H3O
CH3COOHC2 H5 +H2O CH3COOH+C2H5OH
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 In contrast, heterogeneous catalysis describes
processes where the catalysts and substrate
are in distinct phases, typically solid-gas,
respectively.
 Pt(s)
 4NH3+ 5O2 4NO+ 6H2O
 Ni(s)
 CH2=CH2 +H2 CH3 CH3
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 Enzymes are complex proteins performing
catalytic activity in Biological systems.
Zymase
 C6H12O6 + 5O2 CH3COOH + CO2
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Catalysis

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