Question 1

Which of the following affects the activation energy of a reaction?

Accepted Answer

A)   temperature of the reactants
B)   concentrations of reactants
C)   presence of a catalyst
D)   surface area of reactants
E)   reaction progressF) None of the above
G) A) and E) C

Question 2

A catalyst accelerates a reaction because

Accepted Answer

A)   it increases the number of molecules with energy equal to or greater than the activation energy.
B)   it lowers the activation energy for the reaction.
C)   it increases the number of collisions between molecules.
D)   it increases the temperature of the molecules in the reaction.
E)   it supplies energy to reactant molecules.F) B) and D)
G) C) and D)

Question 3

The rate law for the reaction 3A  →\rightarrow→  2B is rate = k[A] with a rate constant of 0.0447 hr¯1. What is the half-life of the reaction?

Accepted Answer

A)   0.0224 hr
B)   0.0645 hr
C)   15.5 hr
D)   22.4 hr
E)   44.7 hr F) A) and D)
G) A) and E)

Question 4

The elementary reaction HBr(g) + Br(g) $\rightarrow$ H(g) + Br2(g) is endothermic.
A) Would you expect the rate constant for the back reaction to be smaller or larger than that for the forward reaction? Explain, briefly.
B) Draw a fully-labeled reaction energy diagram for this reaction, showing the locations of the reactants, products and transition state.

Accepted Answer

a. The back reaction is exothermic. Since the reactions share a common transition state, the activation energy for the back reaction must be smaller than that for the forward reaction. Other things being equal, the rate constant for the back reaction will be larger. b.

Question 5

The units of the rate constant depend on the order of the reaction.

Accepted Answer

A) True 
 B)False

Question 6

Consider the general gas-phase reaction of a molecular substance, A:
1.  At very low pressures many such reactions occur by the following mechanism:
2.  3.  (A* represents a molecule with sufficient energy to overcome the activation energy barrier.)
A) Which of the three reactions above is/are elementary?
B) Where appropriate, identify the molecularity of the reactions.
C) Show that the proposed mechanism is consistent with reaction 1, the observed reaction.
D) Given the mechanism above, suggest a likely rate law for reaction (1).

Accepted Answer

a. Reactions 2 and 3 are elementary. b. ...

Question 7

When a catalyst is added to a reaction mixture, it

Accepted Answer

A)   increases the rate of collisions between reactant molecules.
B)   provides reactant molecules with more energy.
C)   slows down the rate of the back reaction.
D)   provides a new pathway (mechanism)  for the reaction.
E)   None of these choices is correct.F) B) and E)
G) C) and D)

Question 8

In the gas phase at 500.$\degree$C, cyclopropane reacts to form propene in a first-order reaction. The figure shows the natural logarithm of the concentration of cyclopropane (in mol/L) plotted versus time.  a. Explain how this plot confirms that the reaction is first order.
B) Calculate the first-order rate constant, k.
C) Determine the initial concentration of cyclopropane in this experiment.

Accepted Answer

a. The fact that a plot of ln ...

Question 9

In a reversible reaction, a catalyst will speed up the forward reaction but not affect the reverse reaction.

Accepted Answer

A) True 
 B)False

Question 10

An increase in temperature increases the reaction rate because

Accepted Answer

A)   a greater fraction of the collisions have the correct orientation of molecules.
B)   the activation energy of the reaction will increase.
C)   the activation energy of the reaction will decrease.
D)   temperature acts as a catalyst in chemical reactions.
E)   more collisions will have enough energy to exceed the activation energy.F) B) and E)
G) D) and E)

Question 11

The reaction X  →\rightarrow→ Y is first-order overall and first-order with respect to the reactant X. The result of doubling the initial concentration of X will be to

Accepted Answer

A)   shorten the half-life of the reaction.
B)   increase the rate constant of the reaction.
C)   decrease the rate constant of the reaction.
D)   shorten the time taken to reach equilibrium.
E)   double the initial rate. F) B) and E)
G) A) and B)

Question 12

Sulfur trioxide can undergo decomposition according to the equation 
2SO3  →\rightarrow→ 2SO2 + O2
For this reaction, rate = -0 0.5 Δ\DeltaΔ [SO3]/ Δ\DeltaΔ t = k[SO3]2. If the reaction rate is 1.75 *10¯7 mol L¯1 min¯1 when the concentration of sulfur trioxide is 5.4 * 10¯3 mol L¯1, what is the value of the rate constant k?

Accepted Answer

A)   3.2 * 10¯5 L mol¯1 min¯1
B)   1.6 *10¯5 L mol¯1 min¯1
C)   6.0 * 10¯3 L mol¯1 min¯1
D)   3.0 * 10¯3 L mol¯1 min¯1
E)   1.6 * 10¯2 L mol¯1 min¯1 F) A) and B)
G) B) and C)

Question 13

All second-order reactions are bimolecular reactions.

Accepted Answer

A) True 
 B)False

Question 14

A study of the decomposition reaction 3RS2  →\rightarrow→  3R + 6S yields the initial rate data below. What is the rate constant for the reaction? 2  \rightarrow  3R + 6S yields the initial rate data below. What is the rate constant for the reaction?   A)  0.0103 L mol¯1s¯1 B)  0.263 L mol¯1s¯1 C)  0.571 L mol¯1s¯1 D)  1.17 L mol¯1s¯1 E)  1.75 L mol¯1s¯1 " class="answers-bank-image d-inline" rel="preload" >

Accepted Answer

A)   0.0103 L mol¯1s¯1
B)   0.263 L mol¯1s¯1
C)   0.571 L mol¯1s¯1
D)   1.17 L mol¯1s¯1
E)   1.75 L mol¯1s¯1 F) A) and B)
G) B) and E)

Question 15

Sucrose decomposes to fructose and glucose in acid solution. When ln [sucrose] is plotted vs. time, a straight line with slope of -0.208 hr¯1 results. What is the rate law for the reaction?

Accepted Answer

A)   Rate = 0.208 hr¯1 [sucrose]2
B)   Rate = 0.208 hr¯1 [sucrose]
C)   Rate = 0.0433 hr [sucrose]2
D)   Rate = 0.0433 hr [sucrose]
E)   Rate = 0.208 mol L¯1hr¯1 [sucrose]0F) A) and C)
G) A) and E)

Question 16

You are studying the rate of the reaction 2A $\rightarrow$ B and have obtained measurements of the concentration of A at times t = 100, 200, 300, ......, 1000 seconds from the start of the reaction. Carefully describe how you would plot a graph and use it to
A) prove that the reaction is second-order with respect to
A.
B) determine the second-order rate constant k.

Accepted Answer

a. Plot 1/[A] versus time. If ...

Question 17

The half-life of a second-order reaction does not depend on the initial concentration of reactant.

Accepted Answer

A) True 
 B)False

Question 18

A reaction has an activation energy of 195.0 kJ/mol. When the temperature is increased from 200. °\degree° C to 220. °\degree° C, the rate constant will increase by a factor of:

Accepted Answer

A)   1.1
B)   4.3 *104
C)   3.2
D)   7.5
E)   None of these choices is correct. F) C) and D)
G) A) and B)

Question 19

Reaction intermediates differ from activated complexes in that

Accepted Answer

A)   they are stable molecules with normal bonds and are frequently isolated.
B)   they are molecules with normal bonds rather than partial bonds and can occasionally be isolated.
C)   they are intermediate structures which have characteristics of both reactants and products.
D)   they are unstable and can never be isolated.
E)   all reactions involve reaction intermediates, but not all have activated complexes.F) A) and D)
G) B) and E) B

Question 20

When the reaction A  →\rightarrow→  B + C is studied, a plot of ln[A]t vs. time gives a straight line with a negative slope. What is the order of the reaction?

Accepted Answer

A)   zero
B)   first
C)   second
D)   third
E)   More information is needed to determine the order. F) D) and E)
G) B) and E)

Exam 16: Kinetics: Rates and Mechanisms of Chemical Reactions

Which of the following affects the activation energy of a reaction?

Correct Answer
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C

A catalyst accelerates a reaction because

Correct Answer
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The rate law for the reaction 3A $\rightarrow$ 2B is rate = k[A] with a rate constant of 0.0447 hr¯¹. What is the half-life of the reaction?

Correct Answer
verified

The units of the rate constant depend on the order of the reaction.

Correct Answer
verified

Correct Answer
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a. Reactions 2 and 3 are elementary. b. ...
View Answer

When a catalyst is added to a reaction mixture, it

Correct Answer
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Correct Answer
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a. The fact that a plot of ln ...
View Answer

In a reversible reaction, a catalyst will speed up the forward reaction but not affect the reverse reaction.

Correct Answer
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An increase in temperature increases the reaction rate because

Correct Answer
verified

The reaction X $\rightarrow$ Y is first-order overall and first-order with respect to the reactant X. The result of doubling the initial concentration of X will be to

Correct Answer
verified

Correct Answer
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All second-order reactions are bimolecular reactions.

Correct Answer
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Correct Answer
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Sucrose decomposes to fructose and glucose in acid solution. When ln [sucrose] is plotted vs. time, a straight line with slope of -0.208 hr¯¹ results. What is the rate law for the reaction?

Correct Answer
verified

Correct Answer
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a. Plot 1/[A] versus time. If ...
View Answer

The half-life of a second-order reaction does not depend on the initial concentration of reactant.

Correct Answer
verified

A reaction has an activation energy of 195.0 kJ/mol. When the temperature is increased from 200. $\degree$ C to 220. $\degree$ C, the rate constant will increase by a factor of:

Correct Answer
verified

Reaction intermediates differ from activated complexes in that

Correct Answer
verified
B

When the reaction A $\rightarrow$ B + C is studied, a plot of ln[A]_t vs. time gives a straight line with a negative slope. What is the order of the reaction?

Correct Answer
verified

Exam 16: Kinetics: Rates and Mechanisms of Chemical Reactions

Which of the following affects the activation energy of a reaction?

Correct AnswerverifiedC

A catalyst accelerates a reaction because

Correct AnswerverifiedShow Answer

The rate law for the reaction 3A →\rightarrow→ 2B is rate = k[A] with a rate constant of 0.0447 hr¯1. What is the half-life of the reaction?

Correct AnswerverifiedShow Answer

The units of the rate constant depend on the order of the reaction.

Correct AnswerverifiedShow Answer

Correct Answerverifieda. Reactions 2 and 3 are elementary. b. ...View AnswerShow Answer

When a catalyst is added to a reaction mixture, it

Correct AnswerverifiedShow Answer

Correct Answerverifieda. The fact that a plot of ln ...View AnswerShow Answer

In a reversible reaction, a catalyst will speed up the forward reaction but not affect the reverse reaction.

Correct AnswerverifiedShow Answer

An increase in temperature increases the reaction rate because

Correct AnswerverifiedShow Answer

The reaction X →\rightarrow→ Y is first-order overall and first-order with respect to the reactant X. The result of doubling the initial concentration of X will be to

Correct AnswerverifiedShow Answer

Correct AnswerverifiedShow Answer

All second-order reactions are bimolecular reactions.

Correct AnswerverifiedShow Answer

A study of the decomposition reaction 3RS2 →\rightarrow→ 3R + 6S yields the initial rate data below. What is the rate constant for the reaction?

Correct AnswerverifiedShow Answer

Sucrose decomposes to fructose and glucose in acid solution. When ln [sucrose] is plotted vs. time, a straight line with slope of -0.208 hr¯1 results. What is the rate law for the reaction?

Correct AnswerverifiedShow Answer

Correct Answerverifieda. Plot 1/[A] versus time. If ...View AnswerShow Answer

The half-life of a second-order reaction does not depend on the initial concentration of reactant.

Correct AnswerverifiedShow Answer

A reaction has an activation energy of 195.0 kJ/mol. When the temperature is increased from 200. °\degree° C to 220. °\degree° C, the rate constant will increase by a factor of:

Correct AnswerverifiedShow Answer

Reaction intermediates differ from activated complexes in that

Correct AnswerverifiedB

When the reaction A →\rightarrow→ B + C is studied, a plot of ln[A]t vs. time gives a straight line with a negative slope. What is the order of the reaction?

Correct AnswerverifiedShow Answer

Correct Answer
verified
C

Correct Answer
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The rate law for the reaction 3A $\rightarrow$ 2B is rate = k[A] with a rate constant of 0.0447 hr¯¹. What is the half-life of the reaction?

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified
a. Reactions 2 and 3 are elementary. b. ...
View Answer

Correct Answer
verified

Correct Answer
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a. The fact that a plot of ln ...
View Answer

Correct Answer
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Correct Answer
verified

The reaction X $\rightarrow$ Y is first-order overall and first-order with respect to the reactant X. The result of doubling the initial concentration of X will be to

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Sucrose decomposes to fructose and glucose in acid solution. When ln [sucrose] is plotted vs. time, a straight line with slope of -0.208 hr¯¹ results. What is the rate law for the reaction?

Correct Answer
verified

Correct Answer
verified
a. Plot 1/[A] versus time. If ...
View Answer

Correct Answer
verified

A reaction has an activation energy of 195.0 kJ/mol. When the temperature is increased from 200. $\degree$ C to 220. $\degree$ C, the rate constant will increase by a factor of:

Correct Answer
verified

Correct Answer
verified
B

When the reaction A $\rightarrow$ B + C is studied, a plot of ln[A]_t vs. time gives a straight line with a negative slope. What is the order of the reaction?

Correct Answer
verified