Chemical Kinetics
Reaction Rate Expressions
version 2013
Reaction rate expressions take the form:
Rate = k [A]x [B]y [C]z
Where “k” is some numerical constant, [A] is the concentration of A; [B] is the
concentration of B, etc…
(x,y, and z are some whole number that is referred to as the
“order” and indicates the “power” of that particular chemical on the overall rate)
Rate data was obtained for the following reaction at 25oC (does temperature affect
reaction rate so it should be “controlled” or at least recorded? ______)
2A + B + 2C  D + 2E
Experiment
#
Initial
[A]
Initial
[B]
Initial
[C]
Initial rate of
formation of D
1
2
3
4
0.10 M
0.20 M
0.30 M
0.40 M
0.20 M
0.20 M
0.20 M
0.60 M
0.10 M
0.30 M
0.10 M
0.30M
.0004 M/min
.0012 M/min
.0004 M/min
.0036 M/min
This was not a well performed experiment, there are too many things changing at the same time. However, we can still learn from it.
Q1
How much faster is experiment #2 than experiment #1? (how many times)
Q2
How much more concentrated is A in expt #3 than in expt #1? (how many times)
Q3
How much more concentrated is B in expt #2 than in expt #1? (how many times)
Q4
How much more concentrated is C in expt #4 than in expt #3? (how many times)
From examining the answers to these questions (and many more like these) you should be
able to derive and expression (in the form described above) that fits the given information .
TRY IT !!!!!!!
Now try this one:
Rate data was obtained for the following reaction at 25oC
A + B +  C
Experiment
#
Initial
[A]
Initial
[B]
Initial rate of
formation of C
1
2
3
0.10 M
0.10 M
0.20 M
0.10 M
0.20 M
0.20 M
.0006 M/min
.0012 M/min
.0096 M/min
Now try this one:
Rate data was obtained for the following reaction at 25oC
2A + B  C
Experiment
#
Initial
[A]
Initial
[B]
Initial rate of
formation of C
1
2
3
0.10 M
0.20 M
0.20 M
0.20 M
0.20 M
0.10 M
.0003 M/min
.0024 M/min
.0006 M/min
Try # 64 and 66 on page 587 of your textbook(Glencoe)
More practice problems:
(Taken from page 653 of 4th edition General Chem by Whitten, Gailey and Davis)
Rate data was obtained for the following reaction at 25oC
#13)
A + 2B  C +2D
Experiment
#
Initial
[A]
Initial
[B]
Initial rate of
formation of C
1
2
3
4
0.10 M
0.30 M
0.30 M
0.40 M
0.10 M
0.30 M
0.10 M
0.20 M
.0002 M/min
.0006 M/min
.0002 M/min
.0004 M/min
Rate data was obtained for the following reaction at 904oC
#15)
2NO + 2H2  N2 +2H2O
Experiment
#
Initial
[NO]
Initial
[H2]
Initial rate of
formation of N2
0.420 M
0.210 M
0.210 M
0.105 M
0.122 M
0.122 M
0.244 M
0.488 M
0.136 M/s
0.0339 M/s
0.0678 M/s
0.0339 M/s
1
2
3
4
Find the rate-law expression for this reaction.
Find the rate of formation of N2 at the instant when [NO] = 0.550 M and [H2] = 0.199 M
Rate data was obtained for the following reaction at 25oC
#14)
2A + B +2C  D +2E
Experiment
#
Initial
[A]
Initial
[B]
Initial
[C]
Initial rate of
formation of D
1
0.10 M
0.20 M
0.10
5.0 x 10-4 M/min
2
0.20 M
0.20 M
0.30
1.5 x 10-3 M/min
3
0.30 M
0.20 M
0.10
5.0 x 10-4 M/min
4
0.40 M
0.60 M
0.30
4.5 x 10-3 M/min
Find the rate-law expression for this reaction. (including the constant “k”)
The following reaction gives the following information
2NO + O2  2NO2
#16)
Experiment
#
Initial
[NO]
Initial
[O2]
1
2
3
0.020 M
0.040 M
0.020 M
0.010 M
0.010 M
0.040 M
Initial rate of
disappearance of NO
forward rate
calculated
1.0 x 10-4 M/min
4.0 x 10-4 M/min
4.0 x 10-4 M/min
__________
__________
__________
Find the rate-law expression for this reaction. (including the constant “k”)
(Remember that the rate is usually based upon the formation of product not the rate of disappearance of
reactant)
Chemical Kinetics Reaction Rate Expressions ANSWERS
Chemical Kinetics
Reaction Rate Expressions
version 2013
Reaction rate expressions take the form:
Rate = k [A]x [B]y [C]z
Where “k” is some numerical constant, [A] is the concentration of A; [B] is the
concentration of B, etc…
(x,y, and z are some whole number that is referred to as the
“order” and indicates the “power” of that particular chemical on the overall rate)
Rate data was obtained for the following reaction at 25oC (does temperature affect
reaction rate so it should be “controlled” or at least recorded? __YES!____)
2A + B + 2C  D + 2E
Experiment
#
Initial
[A]
Initial
[B]
Initial
[C]
Initial rate of
formation of D
1
2
3
4
0.10 M
0.20 M
0.30 M
0.40 M
0.20 M
0.20 M
0.20 M
0.60 M
0.10 M
0.30 M
0.10 M
0.30M
.0004 M/min
.0012 M/min
.0004 M/min
.0036 M/min
Q1
How much faster is experiment #2 than experiment #1? (how many times) 3X
Q2
How much more concentrated is A in expt #3 than in expt #1? (how many times) 3X
Q3
How much more concentrated is B in expt #2 than in expt #1? (how many times) 1X
Q4
How much more concentrated is C in expt #4 than in expt #3? (how many times) 3X
From examining the answers to these questions (and many more like these) you should be
able to derive and expression (in the form described above) that fits the given information .
TRY IT !!!!!!!
Rate = k [A]0 [B]1 [C]1 ; k=.02 M-1 min-1
Now try this one:
Rate data was obtained for the following reaction at 25oC
A + B +  C
Experiment
#
Initial
[A]
Initial
[B]
Initial rate of
formation of C
1
2
3
0.10 M
0.10 M
0.20 M
0.10 M
0.20 M
0.20 M
.0006 M/min
.0012 M/min
.0096 M/min
Rate = k [A]3 [B]1 ; k= 6.0 M-3 min-1
Now try this one:
Rate data was obtained for the following reaction at 25oC
2A + B  C
Experiment
#
Initial
[A]
Initial
[B]
Initial rate of
formation of C
1
2
3
0.10 M
0.20 M
0.20 M
0.20 M
0.20 M
0.10 M
.0003 M/min
.0024 M/min
.0006 M/min
Rate = k [A]3 [B]2 ; k= 7.5 M-4 min-1
Try # 64 and 66 on page 587 of your textbook(Glencoe)
More practice problems:
(Taken from page 653 of 4th edition General Chem by Whitten, Gailey and Davis)
Rate data was obtained for the following reaction at 25oC
#13)
A + 2B  C +2D
Experiment
#
Initial
[A]
Initial
[B]
Initial rate of
formation of C
1
2
3
4
0.10 M
0.30 M
0.30 M
0.40 M
0.10 M
0.30 M
0.10 M
0.20 M
.0002 M/min
.0006 M/min
.0002 M/min
.0004 M/min
Rate = k [A]0 [B]1 ; k= .002 M0 min-1
Rate data was obtained for the following reaction at 904oC
#15)
2NO + 2H2  N2 +2H2O
Experiment
#
Initial
[NO]
Initial
[H2]
Initial rate of
formation of N2
0.420 M
0.210 M
0.210 M
0.105 M
0.122 M
0.122 M
0.244 M
0.488 M
0.136 M/s
0.0339 M/s
0.0678 M/s
0.0339 M/s
1
2
3
4
Find the rate-law expression for this reaction.
Rate = k [NO]2 [H2]1 ; k= 6.3 M-2 sec-1
Find the rate of formation of N2 at the instant when [NO] = 0.550 M and [H2] = 0.199 M
2
-1
Rate = 6.32 [.55] [.199] ; k= 0.38 M sec
Rate data was obtained for the following reaction at 25oC
#14)
2A + B +2C  D +2E
Experiment
#
Initial
[A]
Initial
[B]
Initial
[C]
Initial rate of
formation of D
1
2
3
4
0.10 M
0.20 M
0.30 M
0.40 M
0.20 M
0.20 M
0.20 M
0.60 M
0.10
0.30
0.10
0.30
5.0 x 10-4 M/min
1.5 x 10-3 M/min
5.0 x 10-4 M/min
4.5 x 10-3 M/min
Find the rate-law expression for this reaction. (including the constant “k”)
Rate = k [A]0 [B]1[C]1 ; k= 0.025 M-1 min-1
The following reaction gives the following information
2NO + O2  2NO2
#16)
Experiment
#
Initial
[NO]
Initial
[O2]
1
2
3
0.020 M
0.040 M
0.020 M
0.010 M
0.010 M
0.040 M
Initial rate of
disappearance of NO
1.0 x 10-4 M/min
4.0 x 10-4 M/min
4.0 x 10-4 M/min
forward rate
calculated
__.0001 M____
__.0004 M____
__.0004 M____
Find the rate-law expression for this reaction. (including the constant “k”)
(Remember that the rate is usually based upon the formation of product not the rate of disappearance of
reactant)
Rate = k [NO]2 [O2]1 ; k= 25.0 M-2 min-1