Chem 162-2011 Lecture 5
1
CHEMISTRY 162-2011
LECTURE 5
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Chem 162-2011 Lecture 5
2
PLAN FOR TODAY
:
COMPLETE LECTURE 4
CHAPTER 13 (cont.) - CHEMICAL KINETICS
H&P 13.7-13.8
•
Collision theory
•
Effect of temperature on reaction rates

Chem 162-2011 Lecture 5
3
FORMULAS
ET: Rate = speed.
Using a diagram with Y being 100 lbs and 110 lbs, and days 0 to 5, show that the increase in weight = slope = (Y
2
– Y
1
)/(X
2
– X
1
) = +2lb/day.
Decrease in weight = -increase in weight = -slope = -(Y
2
– Y
1
)/(X
2
– X
1
) = -2lb/day.
ET: Point out that table in middle of page contains the key formulas in kinetics.
Discuss these formulas at beginning of recitation, focusing on 1
o
reaction.
C
12
H
22
O
11
(sucrose) + H
2
O
→
2 C
6
H
12
O
6
(glucose)
Rate of sucrose disappearance = -(
∆
[sucrose])/(
∆
time) =
-([sucrose
f
] - [sucrose
i
])/(t
f
- t
i
)
Rate of glucose appearance = 2 x Rate of sucrose disappearance
aA + bB
→
cC + dD
General rate of reaction = -(1/a)(
∆
[A]/
∆
t) = -(1/b)(
∆
[B]/
∆
t) = (1/c)(
∆
[C]/
∆
t) = (1/d)(
∆
[D]/
∆
t)
Rate or a reaction may be written several ways.
Reaction: 2A + 3B + C
→
2D
Rate = -k[A]
m
[B]
n
[C]
p
∆
C/
∆
t = -k[A]
m
[B]
n
[C]
p
d[A]/dt = -k[A]
m
[B]
n
[C]
p
Integrated
Reaction
Differentiated
rate law
k
Order
Reaction Rate**
RATE LAW***
(y
=
mx + b)
Half-life
*
units
0
Avg
Rate = -(C
2
-C
1
)/(t
2
-t
1
)
Rate = k[C]
o
=k
[C]
t
= -kt
+ [C]
o
t
1/2
= [C]
o
/2k
M
1
s
-1
1
Avg
Rate = -(C
2
-C
1
)/(t
2
-t
1
)
Rate = k[C]
1
ln[C]
t
= -kt + ln[C]
o
t
1/2
= 0.693/k
M
o
s
-1
2
Avg
Rate = -(C
2
-C
1
)/(t
2
-t
1
)
Rate = k[C]
2
1/[C]
t
=
kt + 1/[C]
o
t
1/2
= 1/(k[C]
o
) M
-1
s
-1
** Rate of appearance = +slope; rate of disappearance = -rate of appearance = -slope.
*** Differentiated Rate Law may be for more than one component, e.g., Rate = k[C]
1
[D]
2
*Half-lives
:
For a zero order reaction, each successive half-life is ½ the time of the preceding one.
For a first order reaction, each successive half-life is equal in time to the preceding one.
For a second order reaction, each successive half-life is double time of the preceding one.
Arrhenius equation:
k = Ae
(-Ea/RT)
A = frequency factor = combination of steric factor and collisional frequency
E
a
= energy of activation
ln k
2
- ln k
1
= (-E
a
/RT
2
) - (-E
a
/RT
1
)
ln k = -E
a
/RT + ln A
ln (k
2
/k
1
) = -(E
a
/R)[(1/T
2
) - (1/T
1
)]

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