Review

1
Review
Reaction mechanism
Br2(l)
C5H12(l)
?
C5H11Br(l)
HBr(l)
2 Br.
h?
step 1
Br2
C5H12 ?
step 2
Br.
HBr C5H11.
C5H11.
Br. ?
C5H11Br
step 3
overall
Br2
C5H12
?
C5H11Br
HBr
2
Br2(l) C5H12(l) ? C5H11Br(l) HBr(l)
2 Br.
h?
step 1
Br2
C5H12 ?
step 2
Br.
HBr C5H11.
?
step 3
C5H11.
C5H11Br
Br.
assume step 2 is rate determining
(slow)
rate k2
Br.
C5H12

Br. intermediate
Br.2 Br2
Keq
rate k2
kBr21/2
C5H12
rate
kBr21/2
C5H12
Br.
Keq1/2
Br21/2
11/2 order reaction
3
bimolecular elementary steps
increase react ?
increase rate of reaction
increase T ?
increase rate of reaction
increase number of collisions
increase force of collisions
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T1
T2 gt T1
molecules
Kinetic Energy
minimum energy required for reaction
activation energy
Ea
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Arrhenius Equation
T dependence of a rate constant, k
k
z
p
e-Ea/RT
Ea activation energy (kJ/mol)
R gas constant (8.314 x 10-3kJ/K mol)
T temperature (K)
z collision frequency
p steric factor (lt1)
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p steric factor
z collision frequency
combine to give A
A
k
e-Ea/RT
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Arrhenius Equation
k A e-Ea/RT
- (Ea/R)
(1/T)
ln k
ln A
- (Ea/R) (1/T) ln A
y m x b
plot ln k
v.s. 1/T
slope -Ea/R
intercept ln A
- 1/T2)
ln (k2/ k1)
(Ea /R)
(1/T1
10
hn
Br2(l) C5H12(l) ? C5H11Br(l) HBr(l)
Ea
Ea
Ea
HBr C5H11. Br.
2Br. C5H12
C5H12 Br2
P.E.
C5H11Br HBr
11
Br2(l) C5H12(l) ? C5H11Br(l) HBr(l)
?Hrxn
lt 0
Ea
?Hrxn
12
Arrhenius Equation
ln k
- (Ea/R) (1/T) ln A
ln K
- (?Ho/R)
?So/R
(1/T)
K
kf/kr
related to ?So
A
orientation factor
Ea
?Ho
related to
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A-B C
A...B...C
activated complex
P.E. is at a maximum
transition state
A B-C
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activated complex
Eaf
Eab
reactants
P.E.
?Hrxn
products
Reaction coordinate
A-B C
A...B...C
A B-C
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activated complex
Eaf
Eab
reactants
P.E.
?Hrxn
products
Reaction coordinate
exothermic
Eab Eaf
gt
endothermic
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activated complex
P.E.
Reaction coordinate
exothermic
Eab Eaf
gt
large Ea
slow rate
endothermic
Eab Eaf
lt
17
- catalyst
catalyst
lowers Eaf ??
faster forward reaction ( kf )
lowers Ear ??
faster reverse reaction ( kr )
kf
and ?H
Keq unchanged
Keq

kr