Deck 16: Kinetics: Rates and Mechanisms of Chemical Reactions

Question 1

For the reaction A(g) + 2B(g) $\rightarrow$ 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

Answer 1

Rate = k[A]

Question 2

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

A) s¯¹
B) mol L¯¹ s¯¹
C) L mol¯¹ s¯¹
D) L² mol¯² s¯¹
E) L³ mol¯³ s¯¹

Answer 2

L² mol¯² s¯¹

Question 3

A study of the decomposition reaction 3RS₂ $\rightarrow$ 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

Answer 3

1.75 L mol¯¹s¯¹

Question 4

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

A) s¯¹
B) L mol¯¹ s¯¹
C) L² mol¯² s¯¹
D) L³ mol¯³ s¯¹
E) mol L¯¹ s¯¹

Question 5

Ammonium cyanate (NH₄CNO) reacts to form urea (NH₂CONH₂). At 65 $\degree$ 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[NH₄CNO]
B) Rate = 3.60 L mol¯¹s¯¹[NH₄CNO]²
C) Rate = 0.28 mol L¯¹s¯¹[NH₄CNO]
D) Rate = 0.28 mol L¯¹s¯¹[NH₄CNO]²
E) Rate = 3.60 L mol¯¹s¯¹[NH₂CONH₂]¯¹

Question 6

Consider this reaction:
2NH₃(g) $\rightarrow$ N₂(g) + 3H₂(g) If the rate $\Delta$ [H₂]/ $\Delta$ t is 0.030 mol L¯¹ s¯¹, then $\Delta$ [NH₃]/ $\Delta$ t 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 is correct.

Question 7

Consider the general reaction:
5Br¯(aq) + BrO₃¯(aq) + 6H⁺(aq) $\rightarrow$ 3Br₂(aq) + 3H₂O(aq)
For this reaction, the rate when expressed as $\Delta$ [Br₂]/ $\Delta$ t is the same as:

A) - $\Delta$ [H₂O]/ $\Delta$ t
B) 3 $\Delta$ [BrO₃¯]/ $\Delta$ t
C) -5 $\Delta$ [Br¯]/ $\Delta$ t
D) -0.6 $\Delta$ [Br¯]/ $\Delta$ t
E) None of these choices is correct.

Question 8

The rate constant for a reaction is 4.65 L mol¯¹s¯¹. What is the overall order of the reaction?

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

Question 9

When the reaction A $\rightarrow$ 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 10

The compound RX₃ decomposes according to the equation 3RX₃ $\rightarrow$ R + R₂X₃ + 3X₂
In an experiment the following data were collected for the decomposition at 100 $\degree$ C. What is the average rate of reaction 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 11

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?

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 12

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 13

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

Question 14

Based on the initial rate data below, what is the value of the rate constant? 2NOBr(g) $\rightarrow$ 2NO(g) + Br₂(g)

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 15

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

A) s¯¹
B) mol L¯¹ s¯¹
C) L mol¯¹ s¯¹
D) mol² L¯² s¯¹
E) L² mol¯² s¯¹

Question 16

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 17

Consider this reaction: 8A(g) + 5B(g) $\rightarrow$ 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 is correct, since its rate of change must be positive.

Question 18

?

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

Question 19

For the reaction 3A(g) + 2B(g) $\rightarrow$ 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 20

For the reaction 2A + B + 2C $\rightarrow$ 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 is correct.

Question 21

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 22

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 23

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)[C₂F₄]
B) Rate = 22.3 (mol L¯¹s)[C₂F₄]
C) Rate = 0.0448 (L mol¯¹s¯¹)[C₂F₄]²
D) Rate = 22.3 (mol L¯¹s)[C₂F₄]²
E) Rate = 0.0448 s¯¹ [C₂F₄]

Question 24

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 is correct.

Question 25

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 * 10⁴ molecules
B) 2.00 * 10¹⁹ molecules
C) 3.20 *10¹⁶ molecules
D) 5.00 * 10²⁰ molecules
E) None of these choices is correct.

Question 26

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 27

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 *10³ years¯¹

Question 28

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 29

The rate constant for the reaction 3A $\rightarrow$ 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 * 10² min

Question 30

A gas-phase decomposition is first-order with respect to the reactant, R. If the initial concentration of R is 1.0 *¯⁴ mol L¯¹ and 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 31

The rate law for the reaction 3A $\rightarrow$ 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 32

The reaction CH₃NC(g) $\rightarrow$ 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 33

The active ingredient in an over-the-counter pain killer analgesic decomposes with a rate constant, k = 9.05 x 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 34

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 35

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 36

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?

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

Question 37

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 is correct.

Question 38

Dinitrogen tetraoxide, N₂O₄, decomposes to nitrogen dioxide, NO₂, in a first-order process. If k = 2.5 * 10³ s¯¹ at -5 $\degree$ C and k = 3.5 * 10⁴ s¯¹ at 25 $\degree$ 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 39

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 40

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

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 41

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 $\degree$ C, in s¯¹?

A) 2.1 *10¹³ s¯¹
B) 6.7 * 10¯²² s¯¹
C) 1.5 * 10¹¹ s¯¹
D) 4.7 *10¯³ s¯¹
E) None of these choices is correct.

Question 42

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 43

What is the molecularity of the following elementary reaction?

A) unimolecular
B) bimolecular
C) termolecular
D) tetramolecular
E) Need to know the reaction order before molecularity can be determined.

Question 44

A boiled egg can be cooked at 100.0 $\degree$ C in exactly 5 minutes. At an altitude of around 2000 m where the boiling point of water is 93.0 $\degree$ 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 45

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 is correct.

Question 46

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 47

Ammonia will react with oxygen in the presence of a copper catalyst to form nitrogen and water. From 164.5 $\degree$ C to 179.0 $\degree$ 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) > 10⁴ kJ/mol

Question 48

(p. Various sections) The gas-phase reaction has been studied in a closed vessel, and the rate equation was found to be: Rate = - $\Delta$ [CH₃NC]/ $\Delta$ t = 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 CH₃NC in the same vessel
D) using a bigger vessel, but the same initial amount of CH₃NC
E) continuously removing CH₃CN as it is formed

Question 49

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

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

Question 50

In going from room temperature (25.0 $\degree$ C) to 10 $\degree$ 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 51

Consider the following mechanism for the oxidation of bromide ions by hydrogen peroxide in aqueous acid solution. Which of the following rate laws is consistent with the mechanism?

A) Rate = k[H₂O₂][H⁺]²[Br¯]
B) Rate = k [H₂O⁺
OH][Br¯]
C) Rate = k[H₂O₂][H⁺][Br¯]
D) Rate = k[HOBr][H⁺][Br¯][H₂O₂]
E) Rate = k[Br¯]

Question 52

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 $\degree$ C to 60 $\degree$ C?

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

Question 53

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 54

Consider the following mechanism for the oxidation of bromide ions by hydrogen peroxide in aqueous acid solution. What is the overall reaction equation for this process?

A) 2H₂O⁺
OH + 2Br¯ $\rightarrow$ H₂O₂ + Br₂ + 2H₂O
B) 2H⁺ + 2Br¯ + H₂O₂ $\rightarrow$ Br₂ + 2H₂O
C) 2H⁺ + H₂O₂ + Br¯ + HOBr $\rightarrow$ H₂O⁺
OH + Br₂ + H₂O
D) H₂O⁺
OH + Br¯ + H⁺ $\rightarrow$ Br₂ + H₂O
E) None of these choices is correct.

Question 55

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

Question 56

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 57

In the gas phase at 500. $\degree$ C, cyclopropane reacts to form propene in a first-order reaction. The figure below shows the concentration of cyclopropane plotted versus time. Use the graph to calculate approximate values of

A) the rate of the reaction, 600. seconds after the start.
B) the half-life of the reaction, t_1/2.

Question 58

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 59

The decomposition of dinitrogen pentaoxide has an activation energy of 102 kJ/mol and $\Delta$ H $\degree$ _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 60

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 61

For each of the following terms/concepts, give a brief explanation or definition. Where possible, use examples.

A) order of a reaction
B) elementary reaction
C) reaction intermediate

Question 62

Briefly outline the key arguments in the collision theory of reaction rates for the elementary reaction products. Show that this theory predicts a second-order rate law, and how it predicts the form of the rate constant k.

Question 63

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

Question 64

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

Question 65

Briefly list the features/properties common to all catalysts and how they work. Draw a labeled reaction energy diagram as part of your answer.

Question 66

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

Question 67

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.

Question 68

The gas-phase conversion of 1,3-butadiene to 1,5-cyclooctadiene, 2C₄H₆ $\rightarrow$ C₈H₁₂, was studied, providing data for the plot shown in the graph, of 1/[butadiene] versus time.

A) Explain how this plot confirms that the reaction is second order.
B) Calculate the second-order rate constant, k.
C) Determine the initial concentration of 1,3-butadiene in this experiment.

Question 69

Is a bimolecular reaction necessarily second-order? Is a second-order reaction necessarily bimolecular? Answer, with explanations and clarifications.

Question 70

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

Question 71

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.

Question 72

In the collision theory of reaction rates, the rate constant for a bimolecular reaction can be written as k = z · p · exp In one sentence each, clearly explain the physical meaning (interpretation) of the following three factors which appear in the above expression:

A) z
B) p
C) exp

Question 73

You are required to determine the energy of activation (E_a) of a reaction. Briefly describe the experimental measurements you would make and how you would obtain the activation energy from a suitable linear plot of the experimental data.

Question 74

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.

Question 75

A chemical reaction of the general type A $\rightarrow$ 2B is first-order, with a rate constant of 1.52 *10¯⁴ s¯¹.

A) Calculate the half-life of A.
B) Assuming the initial concentration of A is 0.067 mol L¯¹, calculate the time needed for the concentration to fall to 0.010 mol L¯¹.

Question 76

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

Question 77

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

Question 78

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).

Question 79

According to the collision theory of reaction rates, what are the three requirements which must be met before an elementary reaction between two molecules can occur?

Question 80

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