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 progress 
A)  temperature of the reactants 
B)  concentrations of reactants 
C)  presence of a catalyst 
D)  surface area of reactants 
E)  reaction progress C

Question 2

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 3

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. 
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. B

Question 4

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

Accepted Answer

A) True 
 B)False

Question 5

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. 
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.

Question 6

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

Question 7

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

Question 8

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

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 
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

Question 9

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 10

Sulfur trioxide can undergo decomposition according to the equation 
2SO3 $\rightarrow$2SO2 + O2
For this reaction, rate = -0 0.5$\Delta$[SO3]/$\Delta$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 
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

Question 11

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

Accepted Answer

A) True 
 B)False

Question 12

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

Question 13

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 14

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. 
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.

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]0 
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]0

Question 16

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 17

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 18

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. 
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.

Question 19

All second-order reactions are bimolecular reactions.

Accepted Answer

A) True 
 B)False

Question 20

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. 
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.

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

Reaction intermediates differ from activated complexes in that

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

A catalyst accelerates a reaction because

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?

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:

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

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?

An increase in temperature increases the reaction rate because

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?

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

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

All second-order reactions are bimolecular reactions.

When a catalyst is added to a reaction mixture, it

Keys to the Study of Chemistry

The Components of Matter

Stoichiometry of Formulas and Equations

Three Major Classes of Chemical Reactions

Gases and the Kinetic-Molecular Theory

Thermochemistry: Energy Flow and Chemical Change

Quantum Theory and Atomic Structure

Electron Configuration and Chemical Periodicity

Models of Chemical Bonding

The Shapes of Molecules

Theories of Covalent Bonding

Intermolecular Forces: Liquids, Solids, and Phase Changes

The Properties of Mixtures: Solutions and Colloids

Periodic Patterns in the Main-Group Elements

Organic Compounds and the Atomic Properties of Carbon

Equilibrium: the Extent of Chemical Reactions

Acid-Base Equilibria

Ionic Equilibria in Aqueous Systems

Thermodynamics: Entropy, Free Energy, and the Direction of Chemical Reactions

Electrochemistry: Chemical Change and Electrical Work

The Elements in Nature and Industry

The Transition Elements and Their Coordination Compounds

Nuclear Reactions and Their Applications

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Exam 16: Kinetics: Rates and Mechanisms of Chemical Reactions

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

Reaction intermediates differ from activated complexes in that

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

A catalyst accelerates a reaction because

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?

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:

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

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

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?

An increase in temperature increases the reaction rate because

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?

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

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

All second-order reactions are bimolecular reactions.

When a catalyst is added to a reaction mixture, it

Keys to the Study of Chemistry

The Components of Matter

Stoichiometry of Formulas and Equations

Three Major Classes of Chemical Reactions

Gases and the Kinetic-Molecular Theory

Thermochemistry: Energy Flow and Chemical Change

Quantum Theory and Atomic Structure

Electron Configuration and Chemical Periodicity

Models of Chemical Bonding

The Shapes of Molecules

Theories of Covalent Bonding

Intermolecular Forces: Liquids, Solids, and Phase Changes

The Properties of Mixtures: Solutions and Colloids

Periodic Patterns in the Main-Group Elements

Organic Compounds and the Atomic Properties of Carbon

Equilibrium: the Extent of Chemical Reactions

Acid-Base Equilibria

Ionic Equilibria in Aqueous Systems

Thermodynamics: Entropy, Free Energy, and the Direction of Chemical Reactions

Electrochemistry: Chemical Change and Electrical Work

The Elements in Nature and Industry

The Transition Elements and Their Coordination Compounds

Nuclear Reactions and Their Applications

Filters

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?

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:

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?

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?

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