Question 1

The reaction of ethylene (C2H4) with butadiene (C4H6) to form cyclohexene (C6H10) has an activation energy (Ea) of 115 kJ/mol. The reverse reaction (decomposition of cyclohexene to ethylene and butadiene) has an activation energy of 287 kJ/mol. What is the heat of reaction, Δ Hrxn, for the forward reaction?

Accepted Answer

A) +115 kJ/mol 
B) +287 kJ/mol 
C) −287 kJ/mol 
D) +172 kJ/mol 
E) −172 kJ/mol

Question 2

A gas-phase decomposition is first-order with respect to the reactant, R. If the initial concentration of R is 1.0 × 10−4 mol L−1and the rate constant k = 1.08 × 10−6 s−1, what concentration of R remains after 25 days?

Accepted Answer

A) 1.0 × 10 −3 mol L −1 
B) 1.0 × 10 −4 mol L −1 
C) 9.6 × 10 −5 mol L −1 
D) 4.3 × 10 −5 mol L −1 
E) 9.7 × 10 −6 mol L −1

Question 3

Ammonium cyanate (NH4CNO) reacts to form urea (NH2CONH2). At 65°C the rate constant, k, is 3.60 L mol−1s−1. What is the rate law for this reaction?

Accepted Answer

A) Rate = 3.60 L mol −1s −1[NH 4CNO] 
B) Rate = 3.60 L mol −1s −1[NH 4CNO] 2 
C) Rate = 0.28 mol L −1 s −1[NH 4CNO] 
D) Rate = 0.28 mol L −1 s −1[NH 4CNO] 2 
E) Rate = 3.60 L mol −1s −1[NH 2CONH 2] −1

Question 4

Consider the following reaction 8A(g) + 5B(g) → 8C(g) + 6D(g)
If [C] is increasing at the rate of 4.0 mol L−1s−1, at what rate is [B] changing?

Accepted Answer

A) −0.40 mol L −1s −1 
B) −2.5 mol L −1s −1 
C) −4.0 mol L −1s −1 
D) −6.4 mol L −1s −1 
E) None of these choices are correct.

Question 5

The rate law for the reaction 3A → C is Rate = 4.36 × 10−2 L mol−1 hr−1 [A]2
What is the half-life for the reaction if the initial concentration of A is 0.250 M?

Accepted Answer

A) 0.0109 hr 
B) 0.0629 hr 
C) 15.9 hr 
D) 23.9 hr 
E) 91.7 hr

Question 6

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

Question 7

The radioactive isotope tritium decays with a first-order rate constant k of 0.056 year−1. What fraction of the tritium initially in a sample is still present 30 years later?

Accepted Answer

A) 0.19 
B) 0.60 
C) 0.15 
D) 2.8 × 10 −38 
E) None of these choices are correct.

Question 8

A transition state is a species (or state) corresponding to an energy maximum on a reaction energy diagram.

Accepted Answer

A) True 
 B)False

Question 9

Consider the reaction 2A + 2B + C → 2D + E
If the rate law for this reaction is Rate = k[A][B]2, what will be the effect on the rate if the concentrations of A, B and C are all doubled at the same time?

Accepted Answer

A) The rate will increase by a factor of 2. 
B) The rate will increase by a factor of 4. 
C) The rate will increase by a factor of 6. 
D) The rate will increase by a factor of 8. 
E) More information is needed before this question can be answered.

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.

Question 11

Chlorine atoms act as heterogeneous catalysts in the destruction of ozone in the stratosphere.

Accepted Answer

A) True 
 B)False

Question 12

Consider the following mechanism for the oxidation of bromide ions by hydrogen peroxide in aqueous acid solution. H+ + H2O2  ⇄ H2O+−OH (rapid equilibrium)H2O+−OH + Br− → HOBr + H2O (slow)HOBr + H+ + Br− → Br2 + H2O (fast)
What is the overall reaction equation for this process?

Accepted Answer

A) 2H 2O +−OH + 2Br − → H 2O 2 + Br 2 + 2H 2O 
B) 2H + + 2Br − + H 2O 2 → Br 2 + 2H 2O 
C) 2H + + H 2O 2 + Br − + HOBr → H 2O +−OH + Br 2 + H 2O 
D) H 2O +−OH + Br − + H + → Br 2 + H 2O 
E) None of these choices are correct.

Question 13

All second-order reactions are bimolecular reactions.

Accepted Answer

A) True 
 B)False

Question 14

If the activation energy of a reaction decreases by 10.0 kJ/mol, from 100.0 to 90.0 kJ/mol, what effect will this have on the rate of reaction at 298K?

Accepted Answer

A) The rate will increase, by a factor of more than 50. 
B) The rate will decrease, by a factor of more than 50. 
C) The rate will increase, by a factor of less than 50. 
D) The rate will decrease, by a factor of less than 50. 
E) The rate will not change unless temperature changes.

Question 15

When the reaction A → B + C is studied, a plot 1/[A]t vs. time gives a straight line with a positive 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.

Question 16

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

Accepted Answer

A) True 
 B)False

Question 17

A reaction has the following rate law: Rate = k[A][B]2
In experiment 1, the concentrations of A and B are both 0.10 mol L−1; in experiment 2, the concentrations are both 0.30 mol L−1. If the temperature stays constant, what is the value of the ratio, Rate(2)/Rate(1)?

Accepted Answer

A) 3.0 
B) 6.0 
C) 9.0 
D) 18 
E) 27

Question 18

A first-order reaction has a half-life of 20.0 minutes. Starting with 1.00 × 1020 molecules of reactant at time t = 0, how many molecules remain unreacted after 100.0 minutes?

Accepted Answer

A) 1.00 × 10 4 molecules 
B) 2.00 × 10 19 molecules 
C) 3.20 × 10 16 molecules 
D) 5.00 × 10 20 molecules 
E) None of these choices are correct.

Question 19

Tetrafluoroethylene, C2F4, can be converted to octafluorocyclobutane which can be used as a refrigerant or an aerosol propellant. A plot of 1/[C2F4] vs. time gives a straight line with a slope of 0.0448 L mol−1s−1. What is the rate law for this reaction?

Accepted Answer

A) Rate = 0.0448 (L mol −1s −1)[C 2F 4] 
B) Rate = 22.3 (mol L −1s)[C 2F 4] 
C) Rate = 0.0448 (L mol −1s −1)[C 2F 4] 2 
D) Rate = 22.3 (mol L −1s)[C 2F 4] 2 
E) Rate = 0.0448 s −1 [C 2F 4]

Question 20

The decomposition of dinitrogen pentaoxide to nitrogen dioxide and oxygen follows first-order kinetics and has an activation energy of 102 kJ/mol. By what factor will the fraction of collisions with energy greater than or equal to the activation energy increase if the reaction temperature goes from 30°C to 60°C?

Accepted Answer

A) 1.00 
B) 1.10 
C) 2.00 
D) 4.00 
E) 38.4

Exam 16: Kinetics: Rates and Mechanisms of Chemical Reactions

A gas-phase decomposition is first-order with respect to the reactant, R. If the initial concentration of R is 1.0 × 10⁻⁴ mol L⁻¹and the rate constant k = 1.08 × 10⁻⁶ s⁻¹, what concentration of R remains after 25 days?

Ammonium cyanate (NH₄CNO) reacts to form urea (NH₂CONH₂) . At 65°C the rate constant, k, is 3.60 L mol⁻¹s⁻¹. What is the rate law for this reaction?

Consider the following reaction 8A(g) + 5B(g) → 8C(g) + 6D(g) If [C] is increasing at the rate of 4.0 mol L⁻¹s⁻¹, at what rate is [B] changing?

The rate law for the reaction 3A → C is Rate = 4.36 × 10⁻² L mol⁻¹hr⁻¹ [A]² What is the half-life for the reaction if the initial concentration of A is 0.250 M?

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

The radioactive isotope tritium decays with a first-order rate constant k of 0.056 year⁻¹. What fraction of the tritium initially in a sample is still present 30 years later?

A transition state is a species (or state) corresponding to an energy maximum on a reaction energy diagram.

Consider the reaction 2A + 2B + C → 2D + E If the rate law for this reaction is Rate = k[A][B]², what will be the effect on the rate if the concentrations of A, B and C are all doubled at the same time?

An increase in temperature increases the reaction rate because

Chlorine atoms act as heterogeneous catalysts in the destruction of ozone in the stratosphere.

All second-order reactions are bimolecular reactions.

If the activation energy of a reaction decreases by 10.0 kJ/mol, from 100.0 to 90.0 kJ/mol, what effect will this have on the rate of reaction at 298K?

When the reaction A → B + C is studied, a plot 1/[A]_t vs. time gives a straight line with a positive slope. What is the order of the reaction?

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

A reaction has the following rate law: Rate = k[A][B]² In experiment 1, the concentrations of A and B are both 0.10 mol L⁻¹; in experiment 2, the concentrations are both 0.30 mol L⁻¹. If the temperature stays constant, what is the value of the ratio, Rate(2) /Rate(1) ?

A first-order reaction has a half-life of 20.0 minutes. Starting with 1.00 × 10²⁰ molecules of reactant at time t = 0, how many molecules remain unreacted after 100.0 minutes?

Tetrafluoroethylene, C₂F₄, can be converted to octafluorocyclobutane which can be used as a refrigerant or an aerosol propellant. A plot of 1/[C₂F₄] vs. time gives a straight line with a slope of 0.0448 L mol⁻¹s⁻¹. What is the rate law for this reaction?

Exam 16: Kinetics: Rates and Mechanisms of Chemical Reactions

A gas-phase decomposition is first-order with respect to the reactant, R. If the initial concentration of R is 1.0 × 10−4 mol L−1and the rate constant k = 1.08 × 10−6 s−1, what concentration of R remains after 25 days?

Ammonium cyanate (NH4CNO) reacts to form urea (NH2CONH2) . At 65°C the rate constant, k, is 3.60 L mol−1s−1. What is the rate law for this reaction?

Consider the following reaction 8A(g) + 5B(g) → 8C(g) + 6D(g) If [C] is increasing at the rate of 4.0 mol L−1s−1, at what rate is [B] changing?

The rate law for the reaction 3A → C is Rate = 4.36 × 10−2 L mol−1 hr−1 [A]2 What is the half-life for the reaction if the initial concentration of A is 0.250 M?

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

The radioactive isotope tritium decays with a first-order rate constant k of 0.056 year−1. What fraction of the tritium initially in a sample is still present 30 years later?

A transition state is a species (or state) corresponding to an energy maximum on a reaction energy diagram.

Consider the reaction 2A + 2B + C → 2D + E If the rate law for this reaction is Rate = k[A][B]2, what will be the effect on the rate if the concentrations of A, B and C are all doubled at the same time?

An increase in temperature increases the reaction rate because

Chlorine atoms act as heterogeneous catalysts in the destruction of ozone in the stratosphere.

Consider the following mechanism for the oxidation of bromide ions by hydrogen peroxide in aqueous acid solution. H+ + H2O2 ⇄ H2O+−OH (rapid equilibrium) H2O+−OH + Br− → HOBr + H2O (slow) HOBr + H+ + Br− → Br2 + H2O (fast) What is the overall reaction equation for this process?

All second-order reactions are bimolecular reactions.

If the activation energy of a reaction decreases by 10.0 kJ/mol, from 100.0 to 90.0 kJ/mol, what effect will this have on the rate of reaction at 298K?

When the reaction A → B + C is studied, a plot 1/[A]t vs. time gives a straight line with a positive slope. What is the order of the reaction?

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

A reaction has the following rate law: Rate = k[A][B]2 In experiment 1, the concentrations of A and B are both 0.10 mol L−1; in experiment 2, the concentrations are both 0.30 mol L−1. If the temperature stays constant, what is the value of the ratio, Rate(2) /Rate(1) ?

A first-order reaction has a half-life of 20.0 minutes. Starting with 1.00 × 1020 molecules of reactant at time t = 0, how many molecules remain unreacted after 100.0 minutes?

Tetrafluoroethylene, C2F4, can be converted to octafluorocyclobutane which can be used as a refrigerant or an aerosol propellant. A plot of 1/[C2F4] vs. time gives a straight line with a slope of 0.0448 L mol−1s−1. What is the rate law for this reaction?

A gas-phase decomposition is first-order with respect to the reactant, R. If the initial concentration of R is 1.0 × 10⁻⁴ mol L⁻¹and the rate constant k = 1.08 × 10⁻⁶ s⁻¹, what concentration of R remains after 25 days?

Ammonium cyanate (NH₄CNO) reacts to form urea (NH₂CONH₂) . At 65°C the rate constant, k, is 3.60 L mol⁻¹s⁻¹. What is the rate law for this reaction?

Consider the following reaction 8A(g) + 5B(g) → 8C(g) + 6D(g) If [C] is increasing at the rate of 4.0 mol L⁻¹s⁻¹, at what rate is [B] changing?

The rate law for the reaction 3A → C is Rate = 4.36 × 10⁻² L mol⁻¹hr⁻¹ [A]² What is the half-life for the reaction if the initial concentration of A is 0.250 M?

The radioactive isotope tritium decays with a first-order rate constant k of 0.056 year⁻¹. What fraction of the tritium initially in a sample is still present 30 years later?

Consider the reaction 2A + 2B + C → 2D + E If the rate law for this reaction is Rate = k[A][B]², what will be the effect on the rate if the concentrations of A, B and C are all doubled at the same time?

When the reaction A → B + C is studied, a plot 1/[A]_t vs. time gives a straight line with a positive slope. What is the order of the reaction?

A reaction has the following rate law: Rate = k[A][B]² In experiment 1, the concentrations of A and B are both 0.10 mol L⁻¹; in experiment 2, the concentrations are both 0.30 mol L⁻¹. If the temperature stays constant, what is the value of the ratio, Rate(2) /Rate(1) ?

A first-order reaction has a half-life of 20.0 minutes. Starting with 1.00 × 10²⁰ molecules of reactant at time t = 0, how many molecules remain unreacted after 100.0 minutes?

Tetrafluoroethylene, C₂F₄, can be converted to octafluorocyclobutane which can be used as a refrigerant or an aerosol propellant. A plot of 1/[C₂F₄] vs. time gives a straight line with a slope of 0.0448 L mol⁻¹s⁻¹. What is the rate law for this reaction?