Quiz 3 1lm2r
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Quiz 3 Due: 11:59pm on Friday, October 5, 2012 Note: You will receive no credit for late submissions. To learn more, read your instructor's Grading Policy
Question 1 Consider the following hypothetical aqueous reaction: total volume of 100.0
. A flask is charged with 0.065
of
. The following data are collected: Time
0
Moles of
0.065 0.051 0.042 0.036 0.031
10
20
30
40
Part A Calculate the number of moles of
at 10
, assuming that there are no molecules of
at time zero.
Express your answer using two significant figures. ANSWER: = 1.4!10"2
Correct
Part B Calculate the number of moles of
at 20
, assuming that there are no molecules of
at time zero.
Express your answer using two significant figures. ANSWER: = 2.3!10"2
Correct
Part C Calculate the number of moles of
at 30
, assuming that there are no molecules of
Express your answer using two significant figures.
at time zero.
in a
ANSWER: = 2.9!10"2
Correct
Part D Calculate the number of moles of
at 40
, assuming that there are no molecules of
at time zero.
Express your answer using two significant figures. ANSWER: = 3.4!10"2
Correct
Part E Calculate the average rate of disappearance of
between
0
and
10
, in units of
.
Express your answer using two significant figures. ANSWER: = 2.3!10"4
Answer Requested
Part F Calculate the average rate of disappearance of
between
Express your answer using two significant figures. ANSWER: = 1.5!10"4
10
and
20
, in units of
.
Correct
Part G Calculate the average rate of disappearance of
between
20
and
30
, in units of
.
30
and
40
, in units of
.
Express your answer using two significant figures. ANSWER: = 1.0!10"4
Correct
Part H Calculate the average rate of disappearance of
between
Express your answer using two significant figures. ANSWER: = 8.3!10"5
All attempts used; correct answer displayed
Part I Between
10
and
30
, what is the average rate of appearance of
that the volume of the solution is constant. Express your answer using two significant figures. ANSWER: = 1.2!10"4
Answer Requested
in units of
? Assume
Question 2 Part A Consider the combustion of
. If hydrogen is burning at the rate of 0.46
, what is the rate of consumption of oxygen? ANSWER: = 0.23
Correct
Part B What is the rate of formation of water vapor? ANSWER: = 0.46
Correct
Part C The reaction
is carried out in a closed vessel. If the partial pressure of
decreasing at the rate of 53 ANSWER: = 27
Correct
Question 3
, what is the rate of change of the total pressure of the vessel?
is
For the reaction
, the initial reaction rate was measured for various initial concentrations of
reactants. The following data were collected: Trial
(
)
(
)
(
Initial rate ( )
)
1
0.20
0.20
0.20
6!10"5
2
0.20
0.20
0.60
1.8!10"4
3
0.40
0.20
0.20
2.4!10"4
4
0.40
0.40
0.20
2.4!10"4
Part A What is the reaction order with respect to
?
Express your answer as an integer.
Hint 1. Compare trial 1 with trial 3 Compare the values in trial 1 to those in trial 3. Notice that
and
remain constant whereas
doubles. What happens to the rate in the transition from trial 1 to trial 3? ANSWER: There is no change. It doubles. It triples. It quadruples.
Hint 2. How to set up the math The reaction rate can be determined from the following equation:
where
is the order with respect to
.
For trial 1 this equation is 2.4!10"4 and for trial 3 this equation is 2.4!10"4 Dividing the equation for trial 3 by that for trial 1 gives
which simplifies to
Now, solve for
.
ANSWER: 2
Correct The rate quadrupled when
was doubled. This indicates an order of 2 with respect to
because
.
Part B What is the reaction order with respect to
?
Express your answer as an integer.
Hint 1. Compare trial 3 with trial 4 Compare the values in trial 3 to those in trial 4. Notice that
and
remain constant whereas
doubled. What happens to the rate in the transition from trial 3 to trial 4? ANSWER: There is no change. It doubles. It triples. It quadruples.
Hint 2. How to set up the math The reaction rate can be determined from the following equation:
where
is the order with respect to
For trial 3 this equation is
.
is
2.4!10"4 and for trial 4 this equation is 2.4!10"4 Dividing the equation for trial 4 by that for trial 3 gives
which simplifies to
Now, solve for .
ANSWER: 0
Correct The rate didn't change when
was doubled. This indicates an order of 0 with respect to
.
Part C What is the reaction order with respect to
?
Express your answer as an integer.
Hint 1. Compare trial 1 with trial 2 Compare the values in trial 1 to those in trial 2. Notice that
and
tripled. What happens to the rate in the transition from trial 1 to trial 2? ANSWER: There is no change. It doubles. It triples. It quadruples.
Hint 2. How to set up the math
remain constant whereas
is
The reaction rate can be determined from the following equation:
where
is the order with respect to
.
For trial 1 this equation is 6!10"5 and for trial 2 this equation is 1.8!10"4 Dividing the equation for trial 2 by that for trial 1 gives
which simplifies to
Now, solve for .
ANSWER: 1
Correct The rate tripled when
was tripled. This indicates an order of 1 with respect to
because
.
Part D What is the value of the rate constant
for this reaction?
Express your answer to three significant figures and include the appropriate units. Indicate the multiplication of units explicitly either with a multiplication dot or a dash.
Hint 1. How to approach the problem Based on your previous answers, and solve for .
. Now, plug in numbers from any one of the trials
ANSWER: 7.50!10"3
All attempts used; correct answer displayed
Question 4 A reaction
obeys the following rate law:
Part A If
is doubled, how will the rate change?
ANSWER: The rate of the reaction would be halved. The rate of the reaction would be multiplied by 4. The rate of the reaction would be doubled. The rate would remain the same.
Correct
Part B Will the rate constant change? ANSWER: Yes No
Correct
.
Part C What is the reaction order for
?
Express your answer as an integer. ANSWER: 0
Correct
Part D What is the reaction order for
?
Express your answer as an integer. ANSWER: 2
Correct
Part E What is the overall reaction order? Express your answer as an integer. ANSWER: 2
Correct
Part F What are the units of the rate constant? ANSWER:
Correct
Question 5 Consider the following reaction: The rate law for this reaction is first order in is 0.050
, the reaction rate at 298
and first order in is 0.0432
Part A What is the value of the rate constant? Express your answer using two significant figures. ANSWER: = 170
Correct
Part B What are the units of the rate constant? ANSWER:
.
. When
is
and
Correct
Part C What would happen to the rate if the concentration of
were tripled?
ANSWER: The rate would be multiplied by 27. The rate would be multiplied by 9. The rate would be tripled. The rate would remain the same.
Correct
Part D What would happen to the rate if the concentration of both reactants were tripled? ANSWER: The rate would be tripled. The rate would be multiplied by 9. The rate would be multiplied by 27. The rate would remain the same.
Correct
Question 6 Consider the gas-phase reaction between nitric oxide and bromine at 273 . The following data for the initial rate of appearance of
were obtained: Initial Rate of Appearance of
Experiment 1
0.10
0.20
24
2
0.25
0.20
150
3
0.10
0.50
60
4
0.35
0.50
735
Part A Determine the rate law. ANSWER:
Correct
Part B Calculate the average value of the rate constant for the appearance of Express your answer using two significant figures. ANSWER: = 1.2!104
Correct
from the four data sets.
Part C How is the rate of appearance of
related to the rate of disappearance of
?
ANSWER: the rate of appearance of
is half the rate of disappearance of
the rate of disappearance of
is half the rate of appearance of
the rate of disappearance of
is equal to the rate of appearance of
Correct
Part D What is the rate of disappearance of
6.7!10"2
when
and
0.29
?
Express your answer using two significant figures. ANSWER: = 7.8
Answer Requested
Question 7 Some watch dials are coated with a phosphor, like replaced by
, and a polymer in which some of the
atoms have been
atoms, tritium. The phosphor emits light when struck by the beta particle from the tritium decay,
causing the dials to glow in the dark. The half-life of tritium is 12.3 yr.
Part A If the light given off is assumed to be directly proportional to the amount of tritium, by how many percents will a dial be dimmed in a watch that is 45 years old? Express your answer to two significant figures and include the appropriate units. ANSWER: 92
Answer Requested
Question 8 Part A How much time is required for a 5.35
sample of
to decay to 0.800
if it has a half-life of 27.8 days?
ANSWER: = 76.2 days
Correct
Question 9 Learning Goal: To learn how graphs can be used to answer kinetics questions. A student collected time ( ) and concentration (
) data at 295
for the reaction
concentration data are shown in the table to the right. The student then plotted graphs of versus
, and
versus
.
. These time and versus
,
( )
(
)
0.00
0.500
0.693
2.00
20.0
0.389
0.944
2.57
40.0
0.303
1.19
3.30
60.0
0.236
1.44
4.24
80.0
0.184
1.69
5.43
Part A What is the order of this reaction?
Hint 1. How to approach the problem Recall that the equation for a straight line takes the form
, where
is the slope and
is the
y intercept. Also consider the following integrated rate law equations: Order
Integrated rate law
Straight line graph vs.
0
vs.
1
vs.
2
If the reaction is zeroth order, a graph of graph of
versus
versus
will be a straight line. If the reaction is first order, a
will be a straight line. If the reaction is second order, a graph of
will be a straight line.
Hint 2. Which graph shows a straight line? Look at each graph shown in the introduction. Which one shows a straight line? ANSWER: versus versus versus
Correct What does a straight line imply about the order of the reaction?
ANSWER: 0 1 2
versus
Correct Now that we know that the reaction is first order, we know that the units of the rate constant will be inverse seconds, .
Part B What is the value of the rate constant for this reaction? Express your answer to three significant figures and include the appropriate units.
Hint 1. Determine how to approach the problem There are two possible ways to solve this problem.Which of the following is not a valid way to approach this problem?
Hint 1. Equation for a line Notice that the integrated rate law
resembles the equation for a straight line
where
is the slope and
corresponds to
,
is the y intercept. That means that
corresponds to
, and
corresponds to ,
corresponds to .
ANSWER: Plug values into the first-order integrated rate law and solve for . Determine the y intercept of the graph of Determine the slope of the graph of
vs. , then change the sign. vs. , then change the sign.
Correct The two valid methods for solving this problem are: Plug values into the first-order integrated rate law and solve for . Determine the slope of the graph of
vs. , then change the sign.
The remaining hints will address the latter method.
Hint 2. How to find the slope of a line The slope of a line is defined as "rise over run" by
Hint 3. Identify the graph components Which components in the graph of
versus
correspond to slope, y intercept, x values, and y
values? Drag each item to the appropriate bin.
Hint 1. Equation for a line Notice that the integrated rate law
resembles the equation for a straight line
where
is the slope and
corresponds to
ANSWER:
,
is the y intercept. That means that
corresponds to
, and
corresponds to ,
corresponds to ..
Answer Requested
ANSWER: = 1.25!10"2
Answer Requested
Next, the student ran the same reaction at a different temperature and measured a different reaction rate, with the following results: (
)
(
)
295
0.0125
325
0.0357
Part C What is the activation energy of this reaction? Express your answer to three significant figures and include the appropriate units.
Hint 1. How to approach the problem The Arrhenius equation relates the rate constant
where
to temperature
is the activation energy,
as follows:
is the gas constant, and
is a constant
called the frequency factor. Notice that this equation also resembles the equation for a straight line,
. So, by plotting the
appropriate values, you can use what you know about a straight line to find the activation energy.
Hint 2. Determine what to plot What relationship will give you points that will plot to a straight line? ANSWER: Plot
vs.
to give a slope of
.
Plot
vs.
to give a slope of
Plot
vs.
to give a slope of
Plot
vs.
Plot
to give a slope of
vs.
to give a slope of
. . . .
Correct
Hint 3. Extend the data table To plot
(
)
on the y axis and
(
)
(
)
295
0.0125
?
?
325
0.0357
?
?
on the x axis, you will need to fill in the rest of the following table:
Hint 4. Determine the slope What is the slope of a plot of
versus
?
Express your answer as an integer and include the appropriate units.
Hint 1. How to find the slope of a line The slope of a line is defined as "rise over run" by the following equation:
Hint 2. Determine the rise What is the value of the "rise"? Express your answer numerically using five significant figures. ANSWER: = 1.0494
Hint 3. Determine the run What is the value of the "run"? Express your answer numerically using five significant figures. ANSWER: = -0.00031291
ANSWER: slope = -3354
Hint 5. Putting it all together We know that the slope is equal to . Solve for Recall that
ANSWER:
3354
. We also know that slope is equal to
.
is the constant equal to 8.314
.
. So,
= 27.9
Answer Requested It is important to realize that the integrated rate law,
in the integrated rate law is not the same as
in the Arrhenius equation. In
refers to the concentration of reactant. In the Arrhenius equation,
is a
constant called the frequency factor.
Question 10 The integrated rate laws for zero-, first-, and second-order reaction may be arranged such that they resemble the equation for a straight line, . Order
Integrated Rate Law
Graph
Slope
0 1 2
Part A The reactant concentration in a zero-order reaction was 0.100
after 190 and 2.00!10"2
after 355 . What
is the rate constant for this reaction? Express your answer with the appropriate units.
Hint 1. How to approach the problem The graph of concentration versus time yields a straight line with a slope of
. Therefore if you treat
the given values as point coordinates, you can calculate the slope of the line formed by connecting those points.
Hint 2. Calculate the rise Slope is equal to "rise over run." What is the value for the rise? Express your answer with the appropriate units.
Hint 1. Formula for the rise
The "rise" is the difference between two points on the y axis. Since for a zero-order reaction the y axis is concentration, simply subtract the two values:
ANSWER: "8.00!10"2
Correct
Hint 3. Calculate the run Slope is equal to "rise over run." What is the value for the run? Express your answer with the appropriate units.
Hint 1. Formula for the run The "run" is the difference between two points on the x axis. Since for a zero-order reaction the x axis is time, simply subtract the two values:
ANSWER: 165
Correct
ANSWER: = 4.85!10"4
Correct
Part B What was the initial reactant concentration for the reaction described in Part A? Express your answer with the appropriate units.
Hint 1. How to approach the problem Use the integrated rate law for zero-order reactions to solve for
. Values for
and
are given in
Part A, and your answer to Part A was the value of .
ANSWER: = 0.192
Correct
Part C The reactant concentration in a first-order reaction was 7.00!10"2
after 40.0 and 8.60!10"3
What is the rate constant for this reaction? Express your answer with the appropriate units.
Hint 1. Make a data table Set up a data table as follows and fill in the missing values. ] (
( )
)
7.00!10"2 8.60!10"3
?
40.0 100
For example, what value goes in the cell marked with a question mark?
after 100 .
ANSWER: -2.66
Answer Requested
Hint 2. Calculate the rise Slope is equal to "rise over run." What is the value for the rise?
Hint 1. Formula for the rise The "rise" is the difference between two points on the y axis. Since the y axis for a first-order reaction is , simply subtract the two values:
ANSWER: -2.10
Correct
Hint 3. Calculate the run Slope is equal to "rise over run." What is the value for the run? Express your answer with the appropriate units.
Hint 1. Formula for the run The "run" is the difference between two points on the x axis. Since the x axis for a first-order reaction is time, simply subtract the two values:
ANSWER:
60.0
Correct
ANSWER: = 3.49!10"2
Answer Requested
Part D The reactant concentration in a second-order reaction was 0.870
after 170 and 2.30!10"2
What is the rate constant for this reaction? Express your answer with the appropriate units.
Hint 1. Make a data table Set up a data table as follows and fill in the missing values.
(
)
0.870
(
) ?
2.30!10"2
( ) 170 880
For example, what value goes in the cell marked with a question mark? ANSWER: 1.15
Hint 2. Calculate the rise Slope is equal to "rise over run." What is the value for the rise?
after 880 .
Hint 1. Formula for the rise The "rise" is the difference between two points on the y axis. Since for a second-order reaction the y axis is , simply subtract the two values:
ANSWER: 42.3
Hint 3. Calculate the run Slope is equal to "rise over run." What is the value for the run? Express your answer with the appropriate units.
Hint 1. Formula for the run The "run" is the difference between two points on the x axis. Since for a second-order reaction the x axis is time, simply subtract the two values:
ANSWER: 710
ANSWER: = 5.96!10"2
Answer Requested
Question 11 Part A
Based on their activation energies and energy changes and assuming that all collision factors are the same, which of the following reactions would be fastest? ANSWER: = 41
,
= -27
.
= 32
,
= -11
.
= 50
,
= 13
.
Correct
Part B Which of the following reactions would be slowest? ANSWER: = 41
,
= -27
= 50
,
= 13
= 32
,
= -11
. . .
Correct
Question 12 The rate of the reaction was measured at several temperatures, and the following data were collected: Temperature 15
0.0521
25
0.101
35
0.184
45
0.332
Part A Using these data, graph
versus
.
ANSWER:
Answer Requested
Part B Calculate the value of
by using your graph.
ANSWER: = 47.5
Correct
Question 13 What is the molecularity of each of the following elementary reactions?
Part A
ANSWER: unimolecular bimolecular termolecular
Correct
Part B
ANSWER: unimolecular bimolecular termolecular
Correct
Part C
ANSWER: unimolecular bimolecular termolecular
Correct
Part D Write the rate law for the reaction in part A? ANSWER:
Correct
Part E Write the rate law for the reaction in part B? ANSWER:
Correct
Part F Write the rate law for the reaction in part C? ANSWER:
Correct
Question 14 Part A Based on the reaction profile, how many intermediates are formed in the reaction
ANSWER: 2
Correct
Part B How many transition states are there? ANSWER: 3
Correct
?
Part C Which step is the fastest? ANSWER:
Correct
Part D Is the reaction
exothermic or endothermic?
ANSWER: exothermic endothermic
Correct
Question 15 The activation energy of an uncatalyzed reaction is 94 energy to 55
. The addition of a catalyst lowers the activation
.
Part A Assuming that the collision factor remains the same, by what factor will the catalyst increase the rate of the reaction at 25 ? Express your answer using two significant figures. ANSWER: = 6.9!106
Correct
Part B Assuming that the collision factor remains the same, by what factor will the catalyst increase the rate of the reaction at 140 ? Express your answer using two significant figures. ANSWER: = 8.6!104
Correct
Score Summary: Your score on this assignment is 75.9%. You received 11.39 out of a possible total of 15 points.
Question 1 Consider the following hypothetical aqueous reaction: total volume of 100.0
. A flask is charged with 0.065
of
. The following data are collected: Time
0
Moles of
0.065 0.051 0.042 0.036 0.031
10
20
30
40
Part A Calculate the number of moles of
at 10
, assuming that there are no molecules of
at time zero.
Express your answer using two significant figures. ANSWER: = 1.4!10"2
Correct
Part B Calculate the number of moles of
at 20
, assuming that there are no molecules of
at time zero.
Express your answer using two significant figures. ANSWER: = 2.3!10"2
Correct
Part C Calculate the number of moles of
at 30
, assuming that there are no molecules of
Express your answer using two significant figures.
at time zero.
in a
ANSWER: = 2.9!10"2
Correct
Part D Calculate the number of moles of
at 40
, assuming that there are no molecules of
at time zero.
Express your answer using two significant figures. ANSWER: = 3.4!10"2
Correct
Part E Calculate the average rate of disappearance of
between
0
and
10
, in units of
.
Express your answer using two significant figures. ANSWER: = 2.3!10"4
Answer Requested
Part F Calculate the average rate of disappearance of
between
Express your answer using two significant figures. ANSWER: = 1.5!10"4
10
and
20
, in units of
.
Correct
Part G Calculate the average rate of disappearance of
between
20
and
30
, in units of
.
30
and
40
, in units of
.
Express your answer using two significant figures. ANSWER: = 1.0!10"4
Correct
Part H Calculate the average rate of disappearance of
between
Express your answer using two significant figures. ANSWER: = 8.3!10"5
All attempts used; correct answer displayed
Part I Between
10
and
30
, what is the average rate of appearance of
that the volume of the solution is constant. Express your answer using two significant figures. ANSWER: = 1.2!10"4
Answer Requested
in units of
? Assume
Question 2 Part A Consider the combustion of
. If hydrogen is burning at the rate of 0.46
, what is the rate of consumption of oxygen? ANSWER: = 0.23
Correct
Part B What is the rate of formation of water vapor? ANSWER: = 0.46
Correct
Part C The reaction
is carried out in a closed vessel. If the partial pressure of
decreasing at the rate of 53 ANSWER: = 27
Correct
Question 3
, what is the rate of change of the total pressure of the vessel?
is
For the reaction
, the initial reaction rate was measured for various initial concentrations of
reactants. The following data were collected: Trial
(
)
(
)
(
Initial rate ( )
)
1
0.20
0.20
0.20
6!10"5
2
0.20
0.20
0.60
1.8!10"4
3
0.40
0.20
0.20
2.4!10"4
4
0.40
0.40
0.20
2.4!10"4
Part A What is the reaction order with respect to
?
Express your answer as an integer.
Hint 1. Compare trial 1 with trial 3 Compare the values in trial 1 to those in trial 3. Notice that
and
remain constant whereas
doubles. What happens to the rate in the transition from trial 1 to trial 3? ANSWER: There is no change. It doubles. It triples. It quadruples.
Hint 2. How to set up the math The reaction rate can be determined from the following equation:
where
is the order with respect to
.
For trial 1 this equation is 2.4!10"4 and for trial 3 this equation is 2.4!10"4 Dividing the equation for trial 3 by that for trial 1 gives
which simplifies to
Now, solve for
.
ANSWER: 2
Correct The rate quadrupled when
was doubled. This indicates an order of 2 with respect to
because
.
Part B What is the reaction order with respect to
?
Express your answer as an integer.
Hint 1. Compare trial 3 with trial 4 Compare the values in trial 3 to those in trial 4. Notice that
and
remain constant whereas
doubled. What happens to the rate in the transition from trial 3 to trial 4? ANSWER: There is no change. It doubles. It triples. It quadruples.
Hint 2. How to set up the math The reaction rate can be determined from the following equation:
where
is the order with respect to
For trial 3 this equation is
.
is
2.4!10"4 and for trial 4 this equation is 2.4!10"4 Dividing the equation for trial 4 by that for trial 3 gives
which simplifies to
Now, solve for .
ANSWER: 0
Correct The rate didn't change when
was doubled. This indicates an order of 0 with respect to
.
Part C What is the reaction order with respect to
?
Express your answer as an integer.
Hint 1. Compare trial 1 with trial 2 Compare the values in trial 1 to those in trial 2. Notice that
and
tripled. What happens to the rate in the transition from trial 1 to trial 2? ANSWER: There is no change. It doubles. It triples. It quadruples.
Hint 2. How to set up the math
remain constant whereas
is
The reaction rate can be determined from the following equation:
where
is the order with respect to
.
For trial 1 this equation is 6!10"5 and for trial 2 this equation is 1.8!10"4 Dividing the equation for trial 2 by that for trial 1 gives
which simplifies to
Now, solve for .
ANSWER: 1
Correct The rate tripled when
was tripled. This indicates an order of 1 with respect to
because
.
Part D What is the value of the rate constant
for this reaction?
Express your answer to three significant figures and include the appropriate units. Indicate the multiplication of units explicitly either with a multiplication dot or a dash.
Hint 1. How to approach the problem Based on your previous answers, and solve for .
. Now, plug in numbers from any one of the trials
ANSWER: 7.50!10"3
All attempts used; correct answer displayed
Question 4 A reaction
obeys the following rate law:
Part A If
is doubled, how will the rate change?
ANSWER: The rate of the reaction would be halved. The rate of the reaction would be multiplied by 4. The rate of the reaction would be doubled. The rate would remain the same.
Correct
Part B Will the rate constant change? ANSWER: Yes No
Correct
.
Part C What is the reaction order for
?
Express your answer as an integer. ANSWER: 0
Correct
Part D What is the reaction order for
?
Express your answer as an integer. ANSWER: 2
Correct
Part E What is the overall reaction order? Express your answer as an integer. ANSWER: 2
Correct
Part F What are the units of the rate constant? ANSWER:
Correct
Question 5 Consider the following reaction: The rate law for this reaction is first order in is 0.050
, the reaction rate at 298
and first order in is 0.0432
Part A What is the value of the rate constant? Express your answer using two significant figures. ANSWER: = 170
Correct
Part B What are the units of the rate constant? ANSWER:
.
. When
is
and
Correct
Part C What would happen to the rate if the concentration of
were tripled?
ANSWER: The rate would be multiplied by 27. The rate would be multiplied by 9. The rate would be tripled. The rate would remain the same.
Correct
Part D What would happen to the rate if the concentration of both reactants were tripled? ANSWER: The rate would be tripled. The rate would be multiplied by 9. The rate would be multiplied by 27. The rate would remain the same.
Correct
Question 6 Consider the gas-phase reaction between nitric oxide and bromine at 273 . The following data for the initial rate of appearance of
were obtained: Initial Rate of Appearance of
Experiment 1
0.10
0.20
24
2
0.25
0.20
150
3
0.10
0.50
60
4
0.35
0.50
735
Part A Determine the rate law. ANSWER:
Correct
Part B Calculate the average value of the rate constant for the appearance of Express your answer using two significant figures. ANSWER: = 1.2!104
Correct
from the four data sets.
Part C How is the rate of appearance of
related to the rate of disappearance of
?
ANSWER: the rate of appearance of
is half the rate of disappearance of
the rate of disappearance of
is half the rate of appearance of
the rate of disappearance of
is equal to the rate of appearance of
Correct
Part D What is the rate of disappearance of
6.7!10"2
when
and
0.29
?
Express your answer using two significant figures. ANSWER: = 7.8
Answer Requested
Question 7 Some watch dials are coated with a phosphor, like replaced by
, and a polymer in which some of the
atoms have been
atoms, tritium. The phosphor emits light when struck by the beta particle from the tritium decay,
causing the dials to glow in the dark. The half-life of tritium is 12.3 yr.
Part A If the light given off is assumed to be directly proportional to the amount of tritium, by how many percents will a dial be dimmed in a watch that is 45 years old? Express your answer to two significant figures and include the appropriate units. ANSWER: 92
Answer Requested
Question 8 Part A How much time is required for a 5.35
sample of
to decay to 0.800
if it has a half-life of 27.8 days?
ANSWER: = 76.2 days
Correct
Question 9 Learning Goal: To learn how graphs can be used to answer kinetics questions. A student collected time ( ) and concentration (
) data at 295
for the reaction
concentration data are shown in the table to the right. The student then plotted graphs of versus
, and
versus
.
. These time and versus
,
( )
(
)
0.00
0.500
0.693
2.00
20.0
0.389
0.944
2.57
40.0
0.303
1.19
3.30
60.0
0.236
1.44
4.24
80.0
0.184
1.69
5.43
Part A What is the order of this reaction?
Hint 1. How to approach the problem Recall that the equation for a straight line takes the form
, where
is the slope and
is the
y intercept. Also consider the following integrated rate law equations: Order
Integrated rate law
Straight line graph vs.
0
vs.
1
vs.
2
If the reaction is zeroth order, a graph of graph of
versus
versus
will be a straight line. If the reaction is first order, a
will be a straight line. If the reaction is second order, a graph of
will be a straight line.
Hint 2. Which graph shows a straight line? Look at each graph shown in the introduction. Which one shows a straight line? ANSWER: versus versus versus
Correct What does a straight line imply about the order of the reaction?
ANSWER: 0 1 2
versus
Correct Now that we know that the reaction is first order, we know that the units of the rate constant will be inverse seconds, .
Part B What is the value of the rate constant for this reaction? Express your answer to three significant figures and include the appropriate units.
Hint 1. Determine how to approach the problem There are two possible ways to solve this problem.Which of the following is not a valid way to approach this problem?
Hint 1. Equation for a line Notice that the integrated rate law
resembles the equation for a straight line
where
is the slope and
corresponds to
,
is the y intercept. That means that
corresponds to
, and
corresponds to ,
corresponds to .
ANSWER: Plug values into the first-order integrated rate law and solve for . Determine the y intercept of the graph of Determine the slope of the graph of
vs. , then change the sign. vs. , then change the sign.
Correct The two valid methods for solving this problem are: Plug values into the first-order integrated rate law and solve for . Determine the slope of the graph of
vs. , then change the sign.
The remaining hints will address the latter method.
Hint 2. How to find the slope of a line The slope of a line is defined as "rise over run" by
Hint 3. Identify the graph components Which components in the graph of
versus
correspond to slope, y intercept, x values, and y
values? Drag each item to the appropriate bin.
Hint 1. Equation for a line Notice that the integrated rate law
resembles the equation for a straight line
where
is the slope and
corresponds to
ANSWER:
,
is the y intercept. That means that
corresponds to
, and
corresponds to ,
corresponds to ..
Answer Requested
ANSWER: = 1.25!10"2
Answer Requested
Next, the student ran the same reaction at a different temperature and measured a different reaction rate, with the following results: (
)
(
)
295
0.0125
325
0.0357
Part C What is the activation energy of this reaction? Express your answer to three significant figures and include the appropriate units.
Hint 1. How to approach the problem The Arrhenius equation relates the rate constant
where
to temperature
is the activation energy,
as follows:
is the gas constant, and
is a constant
called the frequency factor. Notice that this equation also resembles the equation for a straight line,
. So, by plotting the
appropriate values, you can use what you know about a straight line to find the activation energy.
Hint 2. Determine what to plot What relationship will give you points that will plot to a straight line? ANSWER: Plot
vs.
to give a slope of
.
Plot
vs.
to give a slope of
Plot
vs.
to give a slope of
Plot
vs.
Plot
to give a slope of
vs.
to give a slope of
. . . .
Correct
Hint 3. Extend the data table To plot
(
)
on the y axis and
(
)
(
)
295
0.0125
?
?
325
0.0357
?
?
on the x axis, you will need to fill in the rest of the following table:
Hint 4. Determine the slope What is the slope of a plot of
versus
?
Express your answer as an integer and include the appropriate units.
Hint 1. How to find the slope of a line The slope of a line is defined as "rise over run" by the following equation:
Hint 2. Determine the rise What is the value of the "rise"? Express your answer numerically using five significant figures. ANSWER: = 1.0494
Hint 3. Determine the run What is the value of the "run"? Express your answer numerically using five significant figures. ANSWER: = -0.00031291
ANSWER: slope = -3354
Hint 5. Putting it all together We know that the slope is equal to . Solve for Recall that
ANSWER:
3354
. We also know that slope is equal to
.
is the constant equal to 8.314
.
. So,
= 27.9
Answer Requested It is important to realize that the integrated rate law,
in the integrated rate law is not the same as
in the Arrhenius equation. In
refers to the concentration of reactant. In the Arrhenius equation,
is a
constant called the frequency factor.
Question 10 The integrated rate laws for zero-, first-, and second-order reaction may be arranged such that they resemble the equation for a straight line, . Order
Integrated Rate Law
Graph
Slope
0 1 2
Part A The reactant concentration in a zero-order reaction was 0.100
after 190 and 2.00!10"2
after 355 . What
is the rate constant for this reaction? Express your answer with the appropriate units.
Hint 1. How to approach the problem The graph of concentration versus time yields a straight line with a slope of
. Therefore if you treat
the given values as point coordinates, you can calculate the slope of the line formed by connecting those points.
Hint 2. Calculate the rise Slope is equal to "rise over run." What is the value for the rise? Express your answer with the appropriate units.
Hint 1. Formula for the rise
The "rise" is the difference between two points on the y axis. Since for a zero-order reaction the y axis is concentration, simply subtract the two values:
ANSWER: "8.00!10"2
Correct
Hint 3. Calculate the run Slope is equal to "rise over run." What is the value for the run? Express your answer with the appropriate units.
Hint 1. Formula for the run The "run" is the difference between two points on the x axis. Since for a zero-order reaction the x axis is time, simply subtract the two values:
ANSWER: 165
Correct
ANSWER: = 4.85!10"4
Correct
Part B What was the initial reactant concentration for the reaction described in Part A? Express your answer with the appropriate units.
Hint 1. How to approach the problem Use the integrated rate law for zero-order reactions to solve for
. Values for
and
are given in
Part A, and your answer to Part A was the value of .
ANSWER: = 0.192
Correct
Part C The reactant concentration in a first-order reaction was 7.00!10"2
after 40.0 and 8.60!10"3
What is the rate constant for this reaction? Express your answer with the appropriate units.
Hint 1. Make a data table Set up a data table as follows and fill in the missing values. ] (
( )
)
7.00!10"2 8.60!10"3
?
40.0 100
For example, what value goes in the cell marked with a question mark?
after 100 .
ANSWER: -2.66
Answer Requested
Hint 2. Calculate the rise Slope is equal to "rise over run." What is the value for the rise?
Hint 1. Formula for the rise The "rise" is the difference between two points on the y axis. Since the y axis for a first-order reaction is , simply subtract the two values:
ANSWER: -2.10
Correct
Hint 3. Calculate the run Slope is equal to "rise over run." What is the value for the run? Express your answer with the appropriate units.
Hint 1. Formula for the run The "run" is the difference between two points on the x axis. Since the x axis for a first-order reaction is time, simply subtract the two values:
ANSWER:
60.0
Correct
ANSWER: = 3.49!10"2
Answer Requested
Part D The reactant concentration in a second-order reaction was 0.870
after 170 and 2.30!10"2
What is the rate constant for this reaction? Express your answer with the appropriate units.
Hint 1. Make a data table Set up a data table as follows and fill in the missing values.
(
)
0.870
(
) ?
2.30!10"2
( ) 170 880
For example, what value goes in the cell marked with a question mark? ANSWER: 1.15
Hint 2. Calculate the rise Slope is equal to "rise over run." What is the value for the rise?
after 880 .
Hint 1. Formula for the rise The "rise" is the difference between two points on the y axis. Since for a second-order reaction the y axis is , simply subtract the two values:
ANSWER: 42.3
Hint 3. Calculate the run Slope is equal to "rise over run." What is the value for the run? Express your answer with the appropriate units.
Hint 1. Formula for the run The "run" is the difference between two points on the x axis. Since for a second-order reaction the x axis is time, simply subtract the two values:
ANSWER: 710
ANSWER: = 5.96!10"2
Answer Requested
Question 11 Part A
Based on their activation energies and energy changes and assuming that all collision factors are the same, which of the following reactions would be fastest? ANSWER: = 41
,
= -27
.
= 32
,
= -11
.
= 50
,
= 13
.
Correct
Part B Which of the following reactions would be slowest? ANSWER: = 41
,
= -27
= 50
,
= 13
= 32
,
= -11
. . .
Correct
Question 12 The rate of the reaction was measured at several temperatures, and the following data were collected: Temperature 15
0.0521
25
0.101
35
0.184
45
0.332
Part A Using these data, graph
versus
.
ANSWER:
Answer Requested
Part B Calculate the value of
by using your graph.
ANSWER: = 47.5
Correct
Question 13 What is the molecularity of each of the following elementary reactions?
Part A
ANSWER: unimolecular bimolecular termolecular
Correct
Part B
ANSWER: unimolecular bimolecular termolecular
Correct
Part C
ANSWER: unimolecular bimolecular termolecular
Correct
Part D Write the rate law for the reaction in part A? ANSWER:
Correct
Part E Write the rate law for the reaction in part B? ANSWER:
Correct
Part F Write the rate law for the reaction in part C? ANSWER:
Correct
Question 14 Part A Based on the reaction profile, how many intermediates are formed in the reaction
ANSWER: 2
Correct
Part B How many transition states are there? ANSWER: 3
Correct
?
Part C Which step is the fastest? ANSWER:
Correct
Part D Is the reaction
exothermic or endothermic?
ANSWER: exothermic endothermic
Correct
Question 15 The activation energy of an uncatalyzed reaction is 94 energy to 55
. The addition of a catalyst lowers the activation
.
Part A Assuming that the collision factor remains the same, by what factor will the catalyst increase the rate of the reaction at 25 ? Express your answer using two significant figures. ANSWER: = 6.9!106
Correct
Part B Assuming that the collision factor remains the same, by what factor will the catalyst increase the rate of the reaction at 140 ? Express your answer using two significant figures. ANSWER: = 8.6!104
Correct
Score Summary: Your score on this assignment is 75.9%. You received 11.39 out of a possible total of 15 points.
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