1/13/10
1
28
What is the rate constant k?
A) k = 21
B) k = 2.1
!
10
2
M
2
s
1
C) k = 21 M
s
1
D) k = 21 M
2
s
1
E) k = 2.1
!
10
2
M
s
2
To find k, use data from any experiment
(#1)
0.021 mol/Ls = k (0.100 mol/L)
2
(0.100 mol/L)
1
k = 21 (mol/L)
2
s
1
= 21 M
2
s
1
***NEVER REPORT k WITHOUT UNITS
Rate
=
k[NO]
2
[Cl
2
]
2 NO
(g) +
Cl
2
(g)
!
2
NOCl (g)
Rate
=
k[NO]
2
[Cl
2
]
Using method of initial rates determined
29
Given the rate law and [A]
0
,
A
!
products
Consider the simple reaction:
Rate of reaction
=
!
"
[A]
"
t
= k[A]
n
Given [A]
0
and [A]
t
,
How do you find [A]
t
?
How do you find the rate law?
(i)
Firstorder reaction:
!
d[A]
dt
=
k[A]
1
Rate =
1
[A]
d[A]
=
!
kdt
Integrate:
1
[A]
[
A
]
0
[
A
]
t
!
d[A]
=
"
kdt
0
t
!
ln[A]
t
 ln[A]
0
= kt
2.B.
Integrated Rate Laws
(Section 16.4)

Change form of rate law so that reactant concentration
expressed as a function of time
For the reaction :
A
!
products
30
Instantaneous
Rearrange:
31
ln[A]
t
= kt + ln[A]
o
ln
A
[ ]
t
A
[ ]
0
!
"
#
$
%
=
’
kt
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 Winter '10
 Brown
 Chemistry, Reaction, Chemical reaction, Rate equation

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