Deck 14: Chemical Kinetics

Question 1

Under constant conditions, the half-life of a first-order reaction __________.

A)is the time necessary for the reactant concentration to drop to half its original value
B)is constant
C)can be calculated from the reaction rate constant
D)does not depend on the initial reactant concentration
E)All of the above are correct.

Answer 1

All of the above are correct.

Question 2

Nitrogen dioxide decomposes to nitric oxide and oxygen via the reaction: 2NO₂ → 2NO + O₂
In a particular experiment at 300 °C, [NO₂] drops from 0.0100 to 0.00650 M in 100 s. The rate of disappearance of NO₂ for this period is __________ M/s.

A)0.35
B)3.5 × 10^-3
C)3.5 × 10^-5
D)7.0 × 10^-3
E)1.8 × 10^-3

Answer 2

3.5 × 10^-5

Question 3

What is the order of the reaction with respect to ClO₂?

A)1
B)0
C)2
D)3
E)4

Answer 3

2

Question 4

Of the following, all are valid units for a reaction rate except __________.

A)mol/L
B)M/s
C)mol/hr
D)g/s
E)mol/L-hr

Question 5

The reaction CH₃-N≡C → CH₃-C≡N
Is a first-order reaction. At 230.3 °C, k = 6.29 × 10^-4s^-1. If [CH₃-NC] is 1.00 × 10^-3 initially, [CH₃-NC] is __________ after 1.000 × 10³ s.

A)5.33 × 10^-4
B)2.34 × 10^-4
C)1.88 × 10^-3
D)4.27 × 10^-3
E)1.00 × 10^-6

Question 6

A compound decomposes by a first-order process. If 17.0% of the compound decomposes in 60.0 minutes, the half-life of the compound is __________.

A)141 minutes
B)181 minutes
C)198 minutes
D)223 minutes
E)325 minutes

Question 7

The rate law of a reaction is rate = k[D][X]. The units of the rate constant are __________.

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

Question 8

What is the order of the reaction with respect to OH^-?

A)0
B)1
C)2
D)3
E)4

Question 9

The rate law for this reaction is rate = __________.

A)k[A][B]
B)k[P]
C)k[A]²[B]
D)k[A]²[B]²
E)k[A]²

Question 10

The rate law for a reaction is rate = k [A][B]²
Which one of the following statements is false?

A)The reaction is first order in A.
B)The reaction is second order in B.
C)The reaction is second order overall.
D)k is the reaction rate constant
E)If [B] is doubled, the reaction rate will increase by a factor of 4.

Question 11

What is the magnitude of the rate constant for the reaction?

A)1.15 × 10⁴
B)4.6
C)230
D)115
E)713

Question 12

Of the units below, __________ are appropriate for a first-order reaction rate constant.

A)M s^-1
B)s^-1
C)mol/L
D)M^-1 s^-1
E)L mol^-1 s^-1

Question 13

The reaction 2NO₂ → 2NO + O₂
Follows second-order kinetics. At 300°C, [NO₂] drops from 0.0100 M to 0.00650 M in 100.0 s. The rate constant for the reaction is __________ M^-1s^-1.

A)0.096
B)0.65
C)0.81
D)1.2
E)0.54

Question 14

At elevated temperatures, dinitrogen pentoxide decomposes to nitrogen dioxide and oxygen: 2N₂O₅(g)→ 4NO₂ (g)+ O₂ (g)
When the rate of formation of O₂ is 2.2 × 10^-4 M/s, the rate of decomposition of N₂O₅ is __________ M/s.

A)1.1 × 10^-4
B)2.2 × 10^-4
C)2.8 × 10^-4
D)4.4 × 10^-4
E)5.5 × 10^-4

Question 15

Which one of the following graphs shows the correct relationship between concentration and time for a reaction that is second order in [A]?

A)
B)
C)
D)
E)

Question 16

The magnitude of the rate constant is __________.

A)38.0
B)0.278
C)13.2
D)42.0
E)2.21

Question 17

What is the overall order of the reaction?

A)4
B)0
C)1
D)2
E)3

Question 18

A compound decomposes by a first-order process. If 25.0% of the compound decomposes in 60.0 minutes, the half-life of the compound is __________.

A)65 minutes
B)120 minutes
C)145 minutes
D)180 minutes
E)198 minutes

Question 19

A burning splint will burn more vigorously in pure oxygen than in air because

A)oxygen is a reactant in combustion and concentration of oxygen is higher in pure oxygen than is in air.
B)oxygen is a catalyst for combustion.
C)oxygen is a product of combustion.
D)nitrogen is a product of combustion and the system reaches equilibrium at a lower temperature.
E)nitrogen is a reactant in combustion and its low concentration in pure oxygen catalyzes the combustion.

Question 20

Which one of the following is not a valid expression for the rate of the reaction below? 4NH₃ + 7O₂ → 4NO₂ + 6H₂O

A)
B)
C)
D)
E)All of the above are valid expressions of the reaction rate.

Question 21

The following reaction is second order in [A] and the rate constant is 0.039 M^-1s^-1: A → B
The concentration of A was 0.30 M at 23 s. The initial concentration of A was __________ M.

A)2.4
B)0.27
C)0.41
D)3.7
E)1.2 × 10^-2

Question 22

The rate constant for this reaction is __________ s^-1.

A)0.013
B)0.030
C)0.14
D)3.0
E)3.1 × 10^-3

Question 23

The rate constant for this reaction is __________ s^-1.

A)6.9 × 10^-2
B)3.0 × 10^-2
C)14
D)0.46
E)4.0 × 10²

Question 24

The rate constant of a first-order process that has a half-life of 3.50 min is __________ s^-1.

A)0.693
B)1.65 × 10^-2
C)1.98
D).198
E)3.30 × 10^-3

Question 25

The reaction A (aq)→ B (aq)is first order in [A]. A solution is prepared with [A] = 1.22 M. The following data are obtained as the reaction proceeds: The rate constant for this reaction is __________ s^-1.

A)0.23
B)1.0
C)0.17
D)0.12
E)-0.12

Question 26

In general, as temperature goes up, reaction rate __________.

A)goes up if the reaction is exothermic
B)goes up if the reaction is endothermic
C)goes up regardless of whether the reaction is exothermic or endothermic
D)stays the same regardless of whether the reaction is exothermic or endothermic
E)stays the same if the reaction is first order

Question 27

One difference between first- and second-order reactions is that __________.

A)the half-life of a first-order reaction does not depend on [A]₀; the half-life of a second-order reaction does depend on [A]₀
B)the rate of both first-order and second-order reactions do not depend on reactant concentrations
C)the rate of a first-order reaction depends on reactant concentrations; the rate of a second-order reaction does not depend on reactant concentrations
D)a first-order reaction can be catalyzed; a second-order reaction cannot be catalyzed
E)None of the above are true.

Question 28

The rate of a reaction depends on __________.

A)collision frequency
B)collision energy
C)collision orientation
D)all of the above
E)none of the above

Question 29

In the energy profile of a reaction, the species that exists at the maximum on the curve is called the __________.

A)product
B)activated complex
C)activation energy
D)enthalpy of reaction
E)atomic state

Question 30

The following reaction is second order in [A] and the rate constant is 0.025 M^-1s^-1: A → B
The concentration of A was 0.65 M at 33 s. The initial concentration of A was __________ M.

A)2.4
B)0.27
C)0.24
D)1.4
E)1.2 × 10^-2

Question 31

At elevated temperatures, methylisonitrile (CH₃NC)isomerizes to acetonitrile (CH₃CN): CH₃NC (g)→ CH₃CN (g)
The dependence of the rate constant on temperature is studied and the graph below is prepared from the results. The energy of activation of this reaction is __________ kJ/mol.

A)160
B)1.6 × 10⁵
C)4.4 × 10^-7
D)4.4 × 10^-4
E)1.9 × 10⁴

Question 32

As the temperature of a reaction is increased, the rate of the reaction increases because the __________.

A)reactant molecules collide less frequently
B)reactant molecules collide more frequently and with greater energy per collision
C)activation energy is lowered
D)reactant molecules collide less frequently and with greater energy per collision
E)reactant molecules collide more frequently with less energy per collision

Question 33

At elevated temperatures, methylisonitrile (CH₃NC)isomerizes to acetonitrile (CH₃CN): CH₃NC (g)→ CH₃CN (g)
The reaction is first order in methylisonitrile. The attached graph shows data for the reaction obtained at 198.9°C. The rate constant for the reaction is __________ s^-1.

A)-1.9 × 10⁴
B)+1.9 × 10⁴
C)-5.2 × 10^-5
D)+5.2 × 10^-5
E)+6.2

Question 34

In general, as temperature goes down, reaction rate __________.

A)goes down if the reaction is exothermic
B)goes down if the reaction is endothermic
C)stays the same regardless of whether the reaction is exothermic or endothermic
D)goes down regardless of whether the reaction is exothermic or endothermic
E)none of the above

Question 35

Which energy difference in the energy profile below corresponds to the activation energy for the forward reaction?

A)x
B)y
C)x + y
D)x - y
E)y - x

Question 36

The decomposition of N₂O₅ in solution in carbon tetrachloride proceeds via the reaction 2N₂O₅ (soln)→ 4NO₂ (soln)+ O₂ (soln)
The reaction is first order and has a rate constant of 4.82 × 10^-3 s^-1 at 64°C. The rate law for the reaction is rate = __________.

A)k[N₂O₅]²
B)
C)k[N₂O₅]
D)
E)2k[N₂O₅]

Question 37

In the Arrhenius equation, k = Ae^-Ea/RT
__________ is the frequency factor.

A)k
B)A
C)e
D)E_a
E)R

Question 38

The rate constant of a first-order process that has a half-life of 225 s is __________ s^-1.

A)0.693
B)3.08 × 10^-3
C)1.25
D)12.5
E)4.44 × 10^-3

Question 39

The concentration of A is __________ M after 40.0 s.

A)1.3 × 10^-2
B)1.2
C)0.17
D)3.5 × 10^-4
E)0.025

Question 40

The half-life of this reaction is __________ s.

A)0.97
B)7.1
C)5.0
D)3.0
E)0.14

Question 41

Of the following, __________ will lower the activation energy for a reaction.

A)increasing the concentrations of reactants
B)raising the temperature of the reaction
C)adding a catalyst for the reaction
D)removing products as the reaction proceeds
E)increasing the pressure

Question 42

The average rate of disappearance of A between 20 s and 40 s is __________ mol/s.

A)8.5 × 10^-4
B)1.7 × 10^-3
C)590
D)7.1 × 10^-3
E)1.4 × 10^-3

Question 43

The mechanism for formation of the product X is: A + B → C + D (slow)
B + D → X (fast)
The intermediate reactant in the reaction is __________.

A)A
B)B
C)C
D)D
E)X

Question 44

The average rate of disappearance of A between 10 s and 20 s is __________ mol/s.

A)2.2 × 10^-3
B)1.1 × 10^-3
C)4.4 × 10^-3
D)454
E)9.90 × 10^-3

Question 45

Which of the following is true?

A)If we know that a reaction is an elementary reaction, then we know its rate law.
B)The rate-determining step of a reaction is the rate of the fastest elementary step of its mechanism.
C)Since intermediate compounds can be formed, the chemical equations for the elementary reactions in a multistep mechanism do not always have to add to give the chemical equation of the overall process.
D)In a reaction mechanism, an intermediate is identical to an activated complex.
E)All of the above statements are true.

Question 46

The active site of nitrogenase is a cofactor that contains two transition metals. These transition metals are __________.

A)Cr and Mg
B)Mn and V
C)Os and Ir
D)Fe and Zn
E)Fe and Mo

Question 47

For the elementary reaction NO₃ + CO → NO₂ + CO₂
The molecularity of the reaction is __________, and the rate law is rate = __________.

A)2, k[NO₃][CO]
B)4, k[NO₃][CO][NO₂][CO₂]
C)2, k[NO₂][CO₂]
D)2, k[NO₃][CO]/[NO₂][CO₂]
E)4, k[NO₂][CO₂]/[NO₃][CO]

Question 48

The average rate disappearance of A between 20 s and 30 s is __________ mol/s.

A)5.0 × 10^-4
B)1.6 × 10^-2
C)1.5 × 10^-3
D)670
E)0.15

Question 49

The rate law of the overall reaction A + B → C
Is rate = k[A]². Which of the following will not increase the rate of the reaction?

A)increasing the concentration of reactant A
B)increasing the concentration of reactant B
C)increasing the temperature of the reaction
D)adding a catalyst for the reaction
E)All of these will increase the rate.

Question 50

How many moles of B are present at 10 s?

A)0.011
B)0.220
C)0.110
D)0.014
E)1.4 × 10^-3

Question 51

Which substance in the reaction below either appears or disappears the fastest? 4NH₃ + 7O₂ → 4NO₂ + 6H₂O

A)NH₃
B)O₂
C)NO₂
D)H₂O
E)The rates of appearance/disappearance are the same for all of these.

Question 52

__________ are used in automotive catalytic converters.

A)Heterogeneous catalysts
B)Homogeneous catalysts
C)Enzymes
D)Noble gases
E)Nonmetal oxides

Question 53

The primary source of the specificity of enzymes is __________.

A)their polarity, which matches that of their specific substrate
B)their delocalized electron cloud
C)their bonded transition metal, which is specific to the target substrate
D)their locations within the cell
E)their shape, which relates to the lock-and-key model

Question 54

The average rate of appearance of B between 20 s and 30 s is __________ mol/s.

A)+1.5 × 10^-3
B)+5.0 × 10^-4
C)-1.5 × 10^-3
D)+7.3 × 10^-3
E)-7.3 × 10^-3

Question 55

A catalyst can increase the rate of a reaction __________.

A)by changing the value of the frequency factor (A)
B)by increasing the overall activation energy (E_a)of the reaction
C)by lowering the activation energy of the reverse reaction
D)by providing an alternative pathway with a lower activation energy
E)All of these are ways that a catalyst might act to increase the rate of reaction.

Question 56

The enzyme nitrogenase converts __________ into __________.

A)ammonia, urea
B)CO and unburned hydrocarbons, H₂O and CO₂
C)nitrogen, ammonia
D)nitrogen oxides, N₂ and O₂
E)nitroglycerine, nitric acid, and glycerine

Question 57

A possible mechanism for the overall reaction Br₂ (g)+ 2NO (g)→ 2NOBr (g)
Is
NO (g)+ Br₂ (g) NOBr₂ (g)(fast)
NOBr₂ (g)+ NO (g) 2NOBr (slow)
The rate law for formation of NOBr based on this mechanism is rate = __________.

A)k₁[NO]1/2
B)k₁[Br₂]1/2
C)(k₂k₁/k^-1)[NO]²[Br₂]
D)(k₁/k^-1)²[NO]²
E)(k₂k₁/k^-1)[NO]²[Br₂]²

Question 58

Nitrogen fixation is a difficult process because __________.

A)there is so little nitrogen in the atmosphere
B)nitrogen exists in the atmosphere primarily as its oxides which are very unreactive
C)nitrogen is very unreactive, largely due to its triple bond
D)of the extreme toxicity of nitrogen
E)of the high polarity of nitrogen molecules preventing them from dissolving in biological fluids, such as those inside cells

Question 59

Consider the following reaction: 3A → 2B
The average rate of appearance of B is given by Δ[B]/Δt. Comparing the rate of appearance of B and the rate of disappearance of A, we get Δ[B]/Δt = __________ × (-Δ[A]/Δt).

A)-2/3
B)+2/3
C)-3/2
D)+1
E)+3/2

Question 60

Consider the following reaction: A → 2C
The average rate of appearance of C is given by Δ[C]/Δt. Comparing the rate of appearance of C and the rate of disappearance of A, we get Δ[C]/Δt = __________ × (-Δ[A]/Δt).

A)+2
B)-1
C)+1
D)+1/2
E)-1/2

Question 61

The concentration of S₂O₈^2- remaining at 800 s is __________ M.

A)0.046
B)0.076
C)4.00 × 10^-3
D)0.015
E)0.041

Question 62

The concentration of S₂O₈^2- remaining at 400 s is __________ M.

A)+0.015
B)+0.035
C)-0.007
D)+0.045
E)+0.057

Question 63

The average rate of disappearance of I^- between 400.0 s and 800.0 s is __________ M/s.

A)2.8 × 10^-5
B)1.4 × 10^-5
C)5.8 × 10^-5
D)3.6 × 10⁴
E)2.6 × 10^-4

Question 64

At elevated temperatures, dinitrogen pentoxide decomposes to nitrogen dioxide and oxygen: 2N₂O₅(g)→ 4NO₂ (g)+ O₂ (g)
When the rate of formation of NO₂ is 5.5 × 10^-4 M/s, the rate of decomposition of N₂O₅ is ________ M/s.

A)2.2 × 10^-3
B)1.4 × 10^-4
C)10.1 × 10^-4
D)2.8 × 10^-4
E)5.5 × 10^-4

Question 65

A reaction was found to be second order in carbon monoxide concentration. The rate of the reaction __________ if the [CO] is doubled, with everything else kept the same.

A)doubles
B)remains unchanged
C)triples
D)increases by a factor of 4
E)is reduced by a factor of 2

Question 66

The overall order of a reaction is 2. The units of the rate constant for the reaction are __________.

A)M/s
B)M^-1s^-1
C)1/s
D)1/M
E)s/M²

Question 67

A reaction was found to be third order in A. Increasing the concentration of A by a factor of 3 will cause the reaction rate to __________.

A)remain constant
B)increase by a factor of 27
C)increase by a factor of 9
D)triple
E)decrease by a factor of the cube root of 3

Question 68

How many moles of B are present at 30 s?

A)2.4 × 10^-3
B)0.15
C)0.073
D)1.7 × 10^-3
E)0.051

Question 69

If the rate law for the reaction 2A + 3B → products
Is second order in A and first order in B, then the rate law is rate = __________.

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

Question 70

A reaction was found to be zero order in A. Increasing the concentration of A by a factor of 3 will cause the reaction rate to __________.

A)remain constant
B)increase by a factor of 27
C)increase by a factor of 9
D)triple
E)decrease by a factor of the cube root of 3

Question 71

The average rate of disappearance of I^- between 1200.0 s and 1600.0 s is __________ M/s.

A)1.8 × 10^-5
B)1.2 × 10^-5
C)2.0 × 10^-5
D)5.0 × 10⁴
E)1.6 × 10^-4

Question 72

The kinetics of the reaction below were studied and it was determined that the reaction rate increased by a factor of 9 when the concentration of B was tripled. The reaction is __________ order in B. A + B → P

A)zero
B)first
C)second
D)third
E)one-half

Question 73

The average rate of disappearance of I^- in the initial 400.0 s is __________ M/s.

A)6.00
B)3.8 × 10^-5
C)1.4 × 10^-4
D)2.7 × 10⁴
E)3.2 × 10^-4

Question 74

The order of the reaction in B is __________.

A)1
B)2
C)3
D)4
E)0

Question 75

The concentration of S₂O₈^2- remaining at 1600 s is __________ M.

A)0.036
B)0.014
C)0.043
D)0.064
E)0.029

Question 76

If the rate law for the reaction 2A + 3B → products
Is first order in A and second order in B, then the rate law is rate = __________.

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

Question 77

The kinetics of the reaction below were studied and it was determined that the reaction rate did not change when the concentration of B was tripled. The reaction is __________ order in B. A + B → P

A)zero
B)first
C)second
D)third
E)one-half

Question 78

At elevated temperatures, methylisonitrile (CH₃NC)isomerizes to acetonitrile (CH₃CN): CH₃NC (g)→ CH₃CN (g)
At the start of the experiment, there are 0.200 mol of reactant (CH₃NC)and 0 mol of product (CH₃CN)in the reaction vessel. After 25 min of reaction, 0.108 mol of reactant (CH₃NC)remain. The average rate of decomposition of methyl isonitrile, CH₃NC, in this 25 min period is __________ mol/min.

A)3.7 × 10^-3
B)0.092
C)2.3
D)4.3 × 10^-3
E)0.54

Question 79

The overall order of a reaction is 1. The units of the rate constant for the reaction are __________.

A)M/s
B)M^-1s^-1
C)1/s
D)1/M
E)s/M²

Question 80

The order of the reaction in A is __________.

A)1
B)2
C)3
D)4
E)0