Phenomenological chemical kinetics (empirical/classical)

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Phenomenological chemical kinetics
(empirical/classical) -- experimental aspects
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1 Introduction
1.1 details about a chemical reaction
1) Stoichiometric balance of the equation 2)
Thermodynamic Spontaneity and equilibrium 3)
Kinetic Rate and mechanism
The factor concerned by thermodynamics is
the inherent tendency or the possibility and the
advancement of the reaction but not the reality
and the rate.
is spontaneous. Fortunately, this reaction is
too slow to be detectable.
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Thermodynamics and kinetics concern different
aspects of reaction, for example
Thermodynamics reaction direction
(spontaneity) maximum yield (equilibrium). Kineti
cs rate (catalyst, temperature), mechanism
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Chemical kinetics
a branch of chemistry that concerns reaction
rate and mechanism.
Main concerns of chemical kinetics

1. Reaction rate factors that determines the rate
   of reaction, rate law.

2) Reaction mechanism the series of steps by
which a reaction takes place.
3) structure-dependence of reactivity the
correlation between molecular structure and
reaction potential.
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1.2 reaction mechanism and elementary reaction
For multistep reaction
Reaction mechanism / reaction pathway
the detailed way by which the reactants are
converted into products, or the series of steps
by which a reaction takes place.
H2 Br2 2 HBr
H2 I2 2 HI

1. Br2 2 Br
2. Br H2 HBr H
3. H Br2 HBr Br
4. H HBr H2 Br
5. 2 Br Br2

1) I2 2I 2) 2I H2 2HI
The species such as H and Br formed in one step
and consumed in a subsequent step and never seen
as a product is called an intermediate.
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1. Br2 2 Br
2. Br H2 HBr H
3. H Br2 HBr Br
4. H HBr H2 Br
5. 2 Br Br2

The reaction that completes in one act is called
elementary reaction. The sum of the elementary
reactions and their series is called the
mechanism of the overall reaction.
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1.3 Classification of reactions
1) elementary reactions
According to the number of molecules involved
in the reaction, elementary reactions can be
divided into three kinds
unimolecular reaction (decomposition,
isomerization)I2 2I
bimolecular reaction (combinaiton) Br H2 HBr
H
termolecular reaction 2I H2 2HI
The probability of three molecules colliding
simultaneously is very small, termolecular
reaction are quite rare. The elementary reaction
with four reactant molecules in gaseous phase has
not been found.
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2) overall reactions
According to the number of elementary
reactions involved, the overall reaction can be
classified into simple reaction
Diels-Alder addition complex reaction
Ethylene butadiene cyclohexene