Transcript X - Chemistry - Memorial University of Newfoundland

General Chemistry
Principles & Modern Applications
9th Edition
Petrucci/Harwood/Herring/Madura
Chapter 14
Chemical Kinetics
Dr. Travis D. Fridgen
Memorial University of Newfoundland
© 2007 Pearson Education
A particular first order reaction was
monitored over a period of time. The
figure to the right summarizes the
experimental results where each sphere
represents 3.0 mol L-1. The average
reaction rate is (do not use a calculator),
1. 5.0 mol L-1 s-1
2. 1.0 mol L-1 s-1
3. 1.0 s-1
4. 0.20 mol L-1 s-1
5. 0.20 s-1
10 : 00 : 00
10 : 01 : 30
A particular first order reaction was
monitored over a period of time. The
figure to the right summarizes the
experimental results where each sphere
represents 3.0 mol L-1. The average
reaction rate is (do not use a calculator),
1. 5.0 mol L-1 s-1
2. 1.0 mol L-1 s-1
3. 1.0 s-1
4. 0.20 mol L-1 s-1
5. 0.20 s-1
10 : 00 : 00
10 : 01 : 30
1. r =
d[N O 2 ]
2. r =
r=
dt
1 d[N O 2 ]
2
whose rate can be expressed as
d[B r2 ]
d[N O 2 B r]
dt
Consider the following reaction,
2N O 2 B r(g)  
 2N O 2 (g) + B r 2 (g)
=
3. r = 
dt
Equivalent expressions are…
4. r =
=
dt
1 d[N O 2 ]
2
1 d[N O 2 B r]
2
1 d[N O 2 ]
2
dt
=
dt
dt
1 d[N O 2 B r]
2
= 
dt
1 d[N O 2 B r]
2
dt
1. r =
d[N O 2 ]
2. r =
r=
3. r = 
4. r =
1 d[N O 2 B r]
2
1 d[N O 2 ]
=
dt
1 d[NO2 ]
2
=
dt
2
dt
Equivalent expressions are…
dt
1 d[N O 2 ]
2
whose rate can be expressed as
d[B r2 ]
d[N O 2 B r]
dt
Consider the following reaction,
2N O 2 B r(g)  
 2N O 2 (g) + B r 2 (g)
=
dt
dt
1 d[N O 2 B r]
2
= 
dt
1 d[NO2 Br]
2
dt
ln [X]
In the diagram to the right is a plot of the
concentrations of all reactants and
products as a function of time for a
particular reaction.
Which of the following statements is correct?
1. The reaction is second order.
t
2. The blue curve represents the time dependence on a particular product.
3. The rate constant for the reaction could have units of s-1.
4. The product represented by the green line is produced almost twice as fast
as the product represented by the red line.
5. Cannot tell with the information given.
ln [X]
In the diagram to the right is a plot of the
concentrations of all reactants and
products as a function of time for a
particular reaction.
Which of the following statements is correct?
1. The reaction is second order.
t
2. The blue curve represents the time dependence on a particular product.
3. The rate constant for the reaction could have units of s-1.
4. The product represented by the green line is produced almost twice as fast
as the product represented by the red line.
5. Cannot tell with the information given.
Reaction A has a rate constant which is equal
to 16.2 L mol-1 s-1. A plot relating the
concentrations of the reactants and products
with time is plotted for reaction B to the right.
ln [X]
In this question, two reactions are considered.
1. Reaction A is first order and Reaction B is
second order.
2. Reaction A is second order and Reaction B is first order.
3. Both reactions are first order.
4. Both reactions are second order.
t
Reaction A has a rate constant which is equal
to 16.2 L mol-1 s-1. A plot relating the
concentrations of the reactants and products
with time is plotted for reaction B to the right.
ln [X]
In this question, two reactions are considered.
1. Reaction A is first order and Reaction B is
second order.
2. Reaction A is second order and Reaction B is first order.
3. Both reactions are first order.
4. Both reactions are second order.
t
Some data for the decomposition of
dinitrogen pentoxide are plotted to the
right. Which of the following statements
is correct?
0 .5
2 N 2O 5
0 .3
81.7 s
0 .2
2. The rate constant is
1
.
81.7 s
3. The units of the rate constant are s.
81.7 s
0 .1
81.7 s
0 .0
0
4. The reaction is first order in N2O5.
5. The reaction is third order in N2O5.
2N 2 O 4 + O 2
0 .4
[N 2 O 5 ]
1. The rate constant is 81.7 s.

50
100
150
200
tim e / s
250
300
Some data for the decomposition of
dinitrogen pentoxide are plotted to the
right. Which of the following statements
is correct?
0 .5
2 N 2O 5
0 .3
81.7 s
0 .2
2. The rate constant is
1
.
81.7 s
3. The units of the rate constant are s.
81.7 s
0 .1
81.7 s
0 .0
0
4. The reaction is first order in N2O5.
5. The reaction is third order in N2O5.
2N 2 O 4 + O 2
0 .4
[N 2 O 5 ]
1. The rate constant is 81.7 s.

50
100
150
200
tim e / s
250
300
1.
Energy
Energy
X+Y
A+B
X+Y
reaction coordinate
reaction coordinate
4.
Energy
3.
Energy
The reaction between A
and B is determined to be
a fairly fast reaction and
slightly exothermic. Which
of the following potential
energy surfaces fit this
description?
2.
A+B
A+B
X+Y
reaction coordinate
A+B
X+Y
reaction coordinate
1.
Energy
Energy
X+Y
A+B
X+Y
reaction coordinate
reaction coordinate
4.
Energy
3.
Energy
The reaction between A
and B is determined to be
a fairly fast reaction and
only slightly exothermic.
Which of the following
potential energy surfaces
fit this description?
2.
A+B
A+B
X+Y
reaction coordinate
A+B
X+Y
reaction coordinate
Energy
A particular reaction was found to have
forward and reverse activation energies
of 60 and 140 kJ mol-1, respectively. The
enthalpy change for the reaction is, (do
not use a calculator)
R
1. DH = 60 kJ mol-1
2. DH = -60 kJ mol-1
P
3. DH = 80 kJ mol-1
4. DH = -80 kJ mol-1
5. DH = 140 kJ mol-1
reaction coordinate
Energy
A particular reaction was found to have
forward and reverse activation energies
of 60 and 140 kJ mol-1, respectively. The
enthalpy change for the reaction is, (do
not use a calculator)
R
1. DH = 60 kJ mol-1
2. DH = -60 kJ mol-1
P
3. DH = 80 kJ mol-1
4. DH = -80 kJ mol-1
5. DH = 140 kJ mol-1
reaction coordinate
The apparent activation energy for the
chemical reactions which produce light in a
firefly is 50 kJ mol-1. How many times slower
would you expect the firefly to blink if you
cooled down its surroundings from 300 K to
270 K? (You may require your calculator)
1. ~0.1 x
2. ~0.3 x
3. ~3 x
4. ~9 x
5. ~1000 x
The apparent activation energy for the
chemical reactions which produce light in a
firefly is 50 kJ mol-1. How many times slower
would you expect the firefly to blink if you
cooled down its surroundings from 300 K to
270 K? (You may require your calculator)
1. ~0.1 x
2. ~0.3 x
3. ~3 x
4. ~9 x
5. ~1000 x
The exothermic iodide catalyzed decomposition of peroxide was determined to
occur via two separate steps in which the first step is the rate determining step.
Which of the following three potential energy diagrams best summarizes these
findings.
+
1.
2.
R
3.
R
P
P
reaction coordinate
Energy
Energy
Energy
R
P
reaction coordinate
reaction coordinate
The exothermic iodide catalyzed decomposition of peroxide was determined to
occur via two separate steps in which the first step is the rate determining step.
Which of the following three potential energy diagrams best summarizes these
findings.
+
1.
2.
R
3.
R
P
P
reaction coordinate
Energy
Energy
Energy
R
P
reaction coordinate
reaction coordinate
Energy
A schematic of the potential energy
diagram for the reaction of iodine with
hydrogen is shown to the right. Based
on this diagram, which of the following
statements is incorrect.
1. The mechanism for the reaction
could be
I2
2I
H 2 + 2I


2H I
2. Since iodine atoms are intermediate species,
their concentration is undetectable during the
course of the reaction.
3. The second step is the rate-determining step.
4. The overall reaction is exothermic.
+
2
+
2
reaction coordinate
Energy
A schematic of the potential energy
diagram for the reaction of iodine with
hydrogen is shown to the right. Based
on this diagram, which of the following
statements is incorrect.
1. The mechanism for the reaction
could be
I2
2I
H 2 + 2I


2H I
2. Since iodine atoms are intermediate species,
their concentration is undetectable during the
course of the reaction.
3. The second step is the rate-determining step.
4. The overall reaction is exothermic.
+
2
+
2
reaction coordinate
A mechanism for the following reaction
2N O 2 (g) + F2 (g) 
rate = k[N O 2 ][F2 ]
2N O 2 F(g)
1
N O 2 (g) + F2 (g)  
 N O 2 F (g) + F (g)
k
is
1
F (g) + N O 2 (g)  
 N O 2 F (g)
k
slow
fast
Beginning with two moles of NO2 and 1 mole of F2, which of the following
diagrams best represents the mechanism?
[NO2F]
1.
[NO2]
[NO2F]
2.
3.
[F2]
t
[F]
[F]
[X]
[NO2]
[X]
[X]
[NO2]
[NO2F]
[F2]
t
[F2]
t
[F]
A mechanism for the following reaction
2N O 2 (g) + F2 (g) 
rate = k[N O 2 ][F2 ]
2N O 2 F(g)
1
N O 2 (g) + F2 (g)  
 N O 2 F (g) + F (g)
k
is
1
F (g) + N O 2 (g)  
 N O 2 F (g)
k
slow
fast
Beginning with two moles of NO2 and 1 mole of F2, which of the following
diagrams best represents the mechanism?
[NO2F]
1.
[NO2]
[NO2F]
2.
3.
[F2]
t
[F]
[F]
[X]
[NO2]
[X]
[X]
[NO2]
[NO2F]
[F2]
t
[F2]
t
[F]
The Lindemann/Hinshelwood
mechanism for a unimolecular
reaction is given below.
k1
A* + M
1.
A *   P roducts
A steady-state analysis of
the mechanism yields the
following
PM
• at low pressure
rate =
k 1k 2
k -1
[A ]
PM
3.
4.
rate
rate = k 1 [A ][M ]
• at high pressure
2.
rate
k2
rate
k -1
rate
A + M
Which of the following plots represents the
pressure dependence of the rate constant?
PM
PM
The Lindemann/Hinshelwood
mechanism for a unimolecular
reaction is given below.
k1
A* + M
1.
A *   P roducts
A steady-state analysis of
the mechanism yields the
following
PM
• at low pressure
rate =
k 1k 2
k -1
[A ]
PM
3.
4.
rate
rate = k 1 [A ][M ]
• at high pressure
2.
rate
k2
rate
k -1
rate
A + M
Which of the following plots represents the
pressure dependence of the rate constant?
PM
PM
Energy
A+B
X+Y
reaction coordinate
4.
A+B
X+Y
reaction coordinate
Energy
3.
A+B
X+Y
reaction coordinate
Energy
In which diagram to the right
does the dashed line best
represent
the
catalyzed
version of the reaction’s
potential energy profile?
Energy
2.
1.
X+Y
A+B
reaction coordinate
Energy
A+B
X+Y
reaction coordinate
4.
A+B
X+Y
reaction coordinate
Energy
3.
A+B
X+Y
reaction coordinate
Energy
In which diagram to the right
does the dashed line best
represent
the
catalyzed
version of the reaction’s
potential energy profile?
Energy
2.
1.
X+Y
A+B
reaction coordinate