Deck 16: Kinetics: Rates and Mechanisms of Chemical Reactions

Question 1

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

Answer 1

True

Question 2

An elementary reaction is a simple, one-step process.

Answer 2

True

Question 3

All bimolecular reactions are second-order reactions.

Answer 3

True

Question 4

All second-order reactions are bimolecular reactions.

Question 5

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

Question 6

A reaction intermediate is a species corresponding to a local energy maximum on a reaction energy diagram.

Question 7

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

Question 8

The greater the energy of activation, Ea, the faster will be the reaction.

Question 9

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?

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 10

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

Question 11

In the lock and key model of enzyme action, the active site on the enzyme provides an exact fit for the substrate.

Question 12

Consider the reaction 2NH₃(g) → N₂(g) + 3H₂(g)
If the rate Δ[H₂]/Δt is 0.030 mol L⁻¹s⁻¹, then Δ[NH₃ ]/Δt is

A)−0.045 mol L ⁻¹ s ⁻¹
B)−0.030 mol L ⁻¹ s ⁻¹
C)−0.020 mol L ⁻¹ s ⁻¹
D)−0.010 mol L ⁻¹ s ⁻¹
E)None of these choices are correct.

Question 13

Consider the general reaction 5Br⁻(aq) + BrO₃⁻(aq) + 6H⁺(aq) → 3Br₂(aq) + 3H₂O(aq)
For this reaction, the rate when expressed as Δ[Br₂]/Δt is the same as

A)−Δ[H ₂O]/Δt
B)3Δ[BrO ₃ ⁻]/Δt
C)−5Δ[Br ⁻]/Δt
D)−0.6Δ[Br ⁻]/Δt
E)None of these choices are correct.

Question 14

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

Question 15

A catalyst lowers the activation energy but does not affect the mechanism of a reaction.

Question 16

The compound RX₃ decomposes according to the equation 3RX₃ → R + R₂X₃ + 3X₂
In an experiment the following data were collected for the decomposition at 100°C. What is the average rate at which RX₃ is disappearing over the entire experiment?

A)0.011 mol L ⁻¹s ⁻¹
B)0.019 mol L ⁻¹s ⁻¹
C)0.044 mol L ⁻¹s ⁻¹
D)0.049 mol L ⁻¹s ⁻¹
E)0.069 mol L ⁻¹s ⁻¹

Question 17

The rate of a reaction is determined by the rate of the fastest step in the mechanism.

Question 18

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

Question 19

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

Question 20

The rate law cannot be predicted from the stoichiometry of a reaction.

Question 21

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?

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 22

Sulfur trioxide can undergo decomposition according to the equation 2SO₃ → 2SO₂ + O₂
For this reaction, rate = −0.5Δ[SO₃ ]/Δt = 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?

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 23

Sulfuryl chloride, SO₂Cl₂(g), decomposes at high temperature to form SO₂(g) and Cl₂(g). The rate constant at a certain temperature is 4.68 × 10⁻⁵s⁻¹. What is the order of the reaction?

A)Zero
B)First
C)Second
D)Third
E)More information is needed to determine the order.

Question 24

For the reaction A(g) + 2B(g) → 2C(g) + 2D(g)
The following data were collected at constant temperature. Determine the correct rate law for this reaction.

A)Rate = k[A] [B]
B)Rate = k[A] ² [B]
C)Rate = k[A] [B] ²
D)Rate = k[A]
E)Rate = k[A] ³

Question 25

For the reaction A(g) + 2B(g) → 2C(g) + 2D(g)
The following data were collected at constant temperature. Determine the correct rate law for this reaction.

A)Rate = k[A] [B]
B)Rate = k[A] ² [B]
C)Rate = k[A] [B] ²
D)Rate = k[A]
E)Rate = k[A] ³

Question 26

A study of the decomposition reaction 3RS₂ → 3R + 6S yields the following initial rate data. 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

Question 27

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

Question 28

Which of the following sets of units could be appropriate for a zero-order rate constant?

A)s ⁻¹
B)L mol ⁻¹s ⁻¹
C)L ² mol ⁻²s ⁻¹
D)L ³ mol ⁻³s ⁻¹
E)mol L ⁻¹s ⁻¹

Question 29

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?

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 30

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)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 31

A reaction is second-order with respect to the reactant R. Which of the following plots will produce a straight line?

A)[R] vs. 1/time
B)1/[R] vs. time
C)[R] ² vs. time
D)1/[R] ² vs. time
E)ln[R] vs. time

Question 32

When the reaction A → 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)Zero
B)First
C)Second
D)Third
E)More information is needed to determine the order.

Question 33

Which one of the following sets of units is appropriate for a third-order rate constant?

A)s ⁻¹
B)mol L ⁻¹s ⁻¹
C)L mol ⁻¹s ⁻¹
D)L ² mol ⁻²s ⁻¹
E)L ³ mol ⁻³s ⁻¹

Question 34

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)Zero
B)First
C)Second
D)Third
E)More information is needed to determine the order.

Question 35

Which one of the following sets of units is appropriate for a second-order rate constant?

A)s ⁻¹
B)mol L ⁻¹s ⁻¹
C)L mol ⁻¹s ⁻¹
D)mol ² L ⁻²s ⁻¹
E)L ² mol ⁻²s ⁻¹

Question 36

For the reaction 3A(g) + 2B(g) → 2C(g) + 2D(g)
The following data were collected at constant temperature. Determine the correct rate law for this reaction.

A)Rate = k[A][B]
B)Rate = k[A][B] ²
C)Rate = k[A] ³[B] ²
D)Rate = k[A] ^1.5[B]
E)Rate = k[A] ²[B]

Question 37

2NOBr(g) → 2NO(g) + Br₂(g) Based on the initial rate data above, what is the value of the rate constant?

A)0.0360 L mol ⁻¹s ⁻¹
B)0.800 L mol ⁻¹s ⁻¹
C)1.25 L mol ⁻¹s ⁻¹
D)27.8 L mol ⁻¹s ⁻¹
E)0.0360 s ⁻¹

Question 38

The reaction X → 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

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 39

For the reaction 2A + B + 2C → D + E
The following initial rate data were collected at constant temperature. Determine the correct rate law for this reaction. All units are arbitrary.

A)Rate = k[A][B][C]
B)Rate = k[A] ²[B][C]
C)Rate = k[A] ²[B][C] ⁻¹
D)Rate = k[A][B] ²[C] ⁻¹
E)None of these choices are correct.

Question 40

A reaction is first-order with respect to the reactant R. Which of the following plots will produce a straight line?

A)[R] vs. 1/time
B)1/[R] vs. time
C)[R] ² vs. time
D)1/[R] ² vs. time
E)ln[R] vs. time

Question 41

The reaction CH₃NC(g) → CH₃CN(g) is first-order with respect to methyl isocyanide, CH₃NC. If it takes 10.3 minutes for exactly one quarter of the initial amount of methyl isocyanide to react, what is the rate constant in units of min⁻¹?

A)−0.135 min ⁻¹
B)0.0279 min ⁻¹
C)0.089 min ⁻¹
D)0.135 min ⁻¹
E)35.8 min ⁻¹

Question 42

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?

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 43

Dinitrogen tetraoxide, N₂O₄, decomposes to nitrogen dioxide, NO₂, in a first-order process. If k = 2.5 × 10³ s⁻¹ at −5°C and k = 3.5 × 10⁴ s⁻¹ at 25°C, what is the activation energy for the decomposition?

A)0.73 kJ/mol
B)58 kJ/mol
C)140 kJ/mol
D)580 kJ/mol
E)> 1000 kJ/mol

Question 44

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

Question 45

The rate constant for the reaction 3A → 4B is 6.00 × 10⁻³ L mol⁻¹min⁻¹. How long will it take the concentration of A to drop from 0.75 M to 0.25 M?

A)2.2 × 10 ⁻³ min
B)5.5 × 10 ⁻³ min
C)180 min
D)440 min
E)5.0 × 10 ² min

Question 46

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?

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 47

Cyclopropane is converted to propene in a first-order process. The rate constant is 5.4 × 10⁻² hr⁻¹. If the initial concentration of cyclopropane is 0.150 M, what will its concentration be after 22.0 hours?

A)0.0457 M
B)0.105 M
C)0.127 M
D)0.492 M
E)None of these choices are correct.

Question 48

The decomposition of hydrogen peroxide is a first-order process with a rate constant of 1.06 × 10⁻³ min⁻¹. How long will it take for the concentration of H₂O₂ to drop from 0.0200 M to 0.0120 M?

A)< 1 min
B)7.55 min
C)481 min
D)4550 min
E)31,400 min

Question 49

Carbon-14 is a radioactive isotope which decays with a half-life of 5730 years. What is the first-order rate constant for its decay, in units of years⁻¹?

A)5.25 × 10 ⁻⁵ years ⁻¹
B)1.21 × 10 ⁻⁴ years ⁻¹
C)1.75 × 10 ⁻⁴ years ⁻¹
D)3.49 × 10 ⁻⁴ years ⁻¹
E)3.97 × 10 ³ years ⁻¹

Question 50

The active ingredient in an over the counter pain killer analgesic decomposes with a rate constant, k = 9.05 × 10⁻⁴ day⁻¹. How many days does it take for 15% of the original ingredient to decompose?

A)730 days
B)414 days
C)365 days
D)180 days
E)78 days

Question 51

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?

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 52

Ammonia will react with oxygen in the presence of a copper catalyst to form nitrogen and water. From 164.5°C to 179.0°C, the rate constant increases by a factor of 4.27. What is the activation energy of this oxidation reaction?

A)24.5 kJ/mol
B)165 kJ/mol
C)242 kJ/mol
D)1630 kJ/mol
E)> 10 ⁴ kJ/mol

Question 53

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?

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

Question 54

The rate law for the rearrangement of CH₃NC to CH₃CN at 800 K is Rate = (1300 s⁻¹)[CH₃NC]. What is the half-life for this reaction?

A)7.69 × 10 ⁻⁴ s
B)5.3 × 10 ⁻⁴ s
C)1.9 × 10 ⁻³ s
D)520 s
E)1920 s

Question 55

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

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

Question 56

The decomposition of SOCl₂ is first-order in SOCl₂. If the half-life for the reaction is 4.1 hr, how long would it take for the concentration of SOCl₂ to drop from 0.36 M to 0.045 M?

A)0.52 hr
B)1.4 hr
C)12 hr
D)33 hr
E)> 40 hr

Question 57

A reactant R is being consumed in a first-order reaction. What fraction of the initial R is consumed in 4.0 half-lives?

A)0.94
B)0.87
C)0.75
D)0.13
E)0.063

Question 58

A boiled egg can be cooked at 100.0°C in exactly 5 minutes. At an altitude of around 2000 m where the boiling point of water is 93.0°C, it takes exactly 7.5 minutes to cook the egg to the same amount. What is the activation energy for the reaction involved when an egg is boiled?

A)0.5 kJ/mol
B)4.5 kJ/mol
C)7.9 kJ/mol
D)66 kJ/mol
E)>100 kJ/mol

Question 59

In going from room temperature (25.0°C) to 10°C above room temperature, the rate of a reaction doubles. Calculate the activation energy for the reaction.

A)157.2 kJ/mol
B)103.8 kJ/mol
C)52.9 kJ/mol
D)6.4 kJ/mol
E)<1 kJ/mol

Question 60

Butadiene, C₄H₆ (used to make synthetic rubber and latex paints) reacts to C₈H₁₂ with a rate law of rate = 0.014 L/(mol·s) [C₄H₆]². What will be the concentration of C₄H₆ after 3.0 hours if the initial concentration is 0.025 M?

A)0.0052 M
B)0.024 M
C)43 M
D)190 M
E)0.0000 M

Question 61

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?

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

Question 62

The decomposition of dinitrogen pentaoxide has an activation energy of 102 kJ/mol and ΔH°_rxn = + 55 kJ/mol. What is the activation energy for the reverse reaction?

A)27 kJ/mol
B)47 kJ/mol
C)55 kJ/mol
D)102 kJ/mol
E)More information is needed, since this is a Hess's law calculation.

Question 63

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?

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 64

The kinetics of the decomposition of dinitrogen pentaoxide is studied at 50°C and at 75°C. Which of the following statements concerning the studies is correct?

A)The rate at 75°C will be greater than the rate at 50°C because the activation energy will be lower at 75°C than at 50°C.
B)The rate at 75°C will be greater than the rate at 50°C because the activation energy will be higher at 75°C than at 50°C.
C)The rate at 75°C will be less than the rate at 50°C because the molecules at higher speeds do not interact as well as those at lower speeds.
D)The rate at 75°C will be greater than at 50°C because the concentration of a gas increases with increasing temperature.
E)The rate at 75°C will be greater than the rate at 50°C because the number of molecules with enough energy to react increases with increasing temperature.

Question 65

When a catalyst is added to a reaction mixture, it

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 are correct.

Question 66

An increase in temperature increases the reaction rate because

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 67

What is the molecularity of the following elementary reaction? NH₂Cl(aq) + OH⁻ (aq) → NHCl⁻ (aq) + H₂O(l)

A)Unimolecular
B)Bimolecular
C)Termolecular
D)Tetramolecular
E)Need to know the reaction order before molecularity can be determined.

Question 68

In order to obtain the activation energy of a reaction using a graphical method, __________ is plotted against __________, giving a straight line whose slope is equal to __________.

A)k; T; −E _a
B)k; 1/T; −E _a
C)lnk; T; −E _a/R
D)k; 1/T; −E _a/R
E)lnk; 1/T; −E _a/R

Question 69

The reaction of ethylene (C₂H₄) with butadiene (C₄H₆) to form cyclohexene (C₆H₁₀) has an activation energy (E_a) 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 H_rxn, for the forward reaction?

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

Question 70

Reaction intermediates differ from activated complexes in that

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.

Question 71

A catalyst accelerates a reaction because

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 72

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

A)1.1.
B)4.3 × 10 ⁴.
C)3.2.
D)7.5.
E)None of these choices are correct.

Question 73

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?

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 74

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

A)Temperature of the reactants
B)Concentrations of reactants
C)Presence of a catalyst
D)Surface area of reactants
E)Reaction progress

Question 75

The gas-phase reaction CH₃NC → CH₃CN has been studied in a closed vessel, and the rate equation was found to be: Rate = −Δ[CH₃NC]/Δt = k[CH₃NC]. Which one of the following actions is least likely to cause a change in the rate of the reaction?

A)Lowering the temperature
B)Adding a catalyst
C)Using a larger initial amount of CH ₃NC in the same vessel
D)Using a bigger vessel, but the same initial amount of CH ₃NC
E)Continuously removing CH ₃CN as it is formed

Question 76

In an exothermic reaction,

A)the forward reaction is slower than the reverse reaction.
B)the reaction rate will speed up with time.
C)the collision energy of the reactants will be greater than that of the products.
D)the forward reaction will have a lower activation energy than the reverse reaction.
E)the activation energy will change as the reaction progresses.

Question 77

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)
Which of the following rate laws is consistent with the mechanism?

A)Rate = k[H ₂O ₂][H ⁺] ²[Br ⁻]
B)Rate = k[H ₂O ⁺−OH][Br ⁻]
C)Rate = k[H ₂O ₂][H ⁺][Br ⁻]
D)Rate = k[HOBr][H ⁺][Br ⁻][H ₂O ₂]
E)Rate = k[Br ⁻]

Question 78

A rate constant obeys the Arrhenius equation, the factor A being 2.2 ×10¹³ s⁻¹ and the activation energy being 150. kJ mol⁻¹. What is the value of the rate constant at 227°C, in s⁻¹?

A)2.1 × 10 ¹³ s ⁻¹
B)6.7 × 10 ⁻²² s ⁻¹
C)1.5 × 10 ¹¹ s ⁻¹
D)4.7 × 10 ⁻³ s ⁻¹
E)None of these choices are correct.