Deck 15: Chemical Kinetics: the Rates of Chemical Reactions

Question 1

Given the initial rate data for the decomposition reaction,
A $\to$ B + C
Determine the rate expression for the reaction.

A)
B)
C)
D)
E)

Answer 1

Question 2

Which of the following is/are expected to affect the rate of a chemical reaction?
1)Addition of a catalyst.
2)Increasing the reaction temperature.
3)Doubling the volume of the reaction container.

A) 1 only
B) 2 only
C) 3 only
D) 1 and 2
E) 1,2,and 3

Answer 2

1 and 2

Question 3

Nitrosyl chloride is produced from the reaction of nitrogen monoxide and chlorine:
2NO(g)+ Cl₂(g) $\to$ 2NOCl(g)
The following initial rates at a given temperature were obtained for the concentrations listed below.

What is the experimental rate law?

A) Rate = k[Cl₂]
B) Rate = k[NO]
C) Rate = k[NO][Cl₂]²
D) Rate = k[NO]²[Cl₂]
E) Rate = k[NO][Cl₂]^1/2

Answer 3

Rate = k[NO]²[Cl₂]

Question 4

What is the name given to a substance that increases the rate of a chemical reaction but is not itself consumed?

A) catalyst
B) reactant
C) intermediate
D) enthalpy
E) rate constant

Question 5

Which statement concerning relative rates of reaction is correct for the chemical equation given below?
2 CH₃OH(g)+ 3 O₂(g) $\to$ 2 CO₂(g)+ 4 H₂O(g)

A) The rate of disappearance of CH₃OH is equal to the rate of disappearance of O₂.
B) The rate of disappearance of CH₃OH is two times the rate of appearance of H₂O_.
C) The rate of disappearance of CH₃OH is half the rate of appearance of CO₂.
D) The rate of appearance of H₂O is two times the rate of appearance of CO₂.
E) The rate of appearance of H₂O is four times the rate of disappearance of CH₃OH.

Question 6

Which of the following conclusions concerning the concentration-time plot provided below is/are correct?
1)The concentration of substance D is decreasing over time.
2)The instantaneous reaction rate at point A is less than the instantaneous reaction rate at point B.
3)Substance D is a product of the reaction.

A) 1 only
B) 2 only
C) 3 only
D) 1 and 3
E) 1,2,and 3

Question 7

For the reaction provided,the rate of disappearance of IO₃^-(aq)at a particular time and concentration is 2.3 $\times$ 10^-3 mol/L·s.
IO₃^-(aq)+ 5I^-(aq) + 6H⁺(aq) $\to$ 3I₂(aq)+ 3H₂O(l)
What is the relative rate of appearance of I₂(aq)?

A) 7.7 $\times$ 10^-3 mol/L·s
B) 2.3 $\times$ 10^-3 mol/L·s
C) -6.9 $\times$ 10^-3 mol/L·s
D) 6.9 $\times$ 10^-3 mol/L·s
E) 1.3 $\times$ 10^-3 mol/L·s

Question 8

Given the initial rate data for the reaction A + B $\to$ C,determine the rate expression for the reaction.

A)
B)
C)
D)
E)

Question 9

Assume the reaction below
2 NO(g)+ O₂(g) $\to$ 2 NO₂(g)
Proceeds via the following rate expression:
Which of the following statements concerning the above chemical reaction and rate equation is/are CORRECT?
1)The reaction is second-order with respect to NO.
2)The rate of disappearance of O₂ is two times the rate of appearance of NO₂.
3)According to the balanced chemical equation,the reaction is fifth-order overall.

A) 1 only
B) 2 only
C) 3 only
D) 1 and 3
E) 2 and 3

Question 10

The following data were obtained in a kinetics study of the hypothetical reaction A + B + C $\to$ products.

Using the initial-rate method,what is the order of the reaction with respect to B?

A) zero-order
B) first-order
C) second-order
D) third-order
E) impossible to tell from the data given

Question 11

Given the initial rate data for the reaction A + B $\to$ C,determine the rate expression for the reaction.

A)
B)
C)
D)
E)

Question 12

What is the overall order of the reaction below
NO(g)+ O₃(g) $\to$ NO₂(g)+ O₂(g)
If it proceeds via the following rate expression?

A) zero-order
B) first-order
C) second-order
D) third-order
E) fourth-order

Question 13

Which of the following expressions does not represent a proper expression for the rate of this reaction?
2A + 3B $\to$ F + 2G

A)
B)
C)
D)
E)

Question 14

For a certain overall third-order reaction with the general form aA $\to$ products,the initial rate of reaction is 0.42 M·s^-1 when the initial concentration of the reactant is 0.25 M.What is the rate constant for this reaction?

A) 0.0093 M^-2.s^-1
B) 27 M^-2.s^-1
C) 0.42 M^-2.s^-1
D) 0.15 M^-2.s^-1
E) 110 M^-2.s^-1

Question 15

Consider the exothermic combustion of coal.Which of the following could increase the rate of reaction?

A) using smaller pieces of coal
B) increasing the concentration of oxygen
C) lowering the temperature
D) both (a)and (b)are correct
E) choices (a),(b)and (c)are all correct

Question 16

The rate law for a reaction is rate = k[A]²[B].Which of the following mixtures of reactants will give the $\underline{\text{ smallest initial rate? }}$

A) 1.0 M A,1.0 M B
B) 2.0 M A,0.50 M B
C) 0.50 M A,0.50 M B
D) 0.125 M A,3.0 M B
E) 1.5 M A,0.50 M B

Question 17

Which relationship correctly compares the rates of the following reactants and products?
2 NOCl(g) $\to$ 2 NO(g)+ Cl₂(g)

A)
B)
C)
D)
E)

Question 18

The average rate of disappearance of ozone in the following reaction is found to be atm/s.
What is the rate of appearance of
During this interval?

A) atm/s
B) atm/s
C) atm/s
D) atm/s
E) atm/s

Question 19

The reactants A and B are mixed,and the reaction is timed until a color change occurs.The data are as follows:

The order of the reaction with respect to reactant A is

A) 2.
B) .
C) 1.
D) .
E) 0.

Question 20

If a reaction is third-order with respect to a particular reactant,when the concentration of that reactant is decreased by a factor of 2,the reaction rate will _____.

A) decrease by a factor of .
B) remain constant.
C) increase by a factor of 8.
D) decrease by a factor of .
E) increase by a factor of 4.

Question 21

How are the exponents in a rate law determined?

A) They are equal to the inverse of the coefficients in the overall balanced chemical equation.
B) They are determined by experimentation.
C) They are equal to the coefficients in the overall balanced chemical equation.
D) They are equal to the reactant concentrations.
E) They are equal to the ln(2)divided by the rate constant.

Question 22

For the first-order decomposition of N₂O₅ at a high temperature,determine the rate constant if the N₂O₅ concentration decreases from 1.04 M to 0.62 M in 375 seconds.

A) 5.99 $\times$ 10^-4 s^-1
B) 1.59 $\times$ 10^-3 s^-1
C) 1.74 $\times$ 10^-3 s^-1
D) 1.38 $\times$ 10^-3 s^-1
E) 1.94 $\times$ 10² s^-1

Question 23

Given the initial rate data for the reaction A + B $\to$ C,determine the rate expression for the reaction.

A)
B)
C)
D)
E)

Question 24

In a first-order reaction,the half-life is 137 minutes.What is the rate constant?

A) 1.22 $\times$ 10^-4 s^-1
B) 5790 s^-1
C) 0.304 s^-1
D) 5.06 $\times$ 10^-3 s^-1
E) 8.43 $\times$ 10^-5 s^-1

Question 25

Which of the following units are consistent with the units of the reaction rate in a first order reaction?

A)
B)
C)
D)
E)

Question 26

For a reaction,A $\to$ B + C,which of the following equations corresponds to the integrated expression for a second-order decomposition reaction?

A)
B)
C)
D)
E)

Question 27

Which of the following is $\underline{\text{ not }}$ a correct representation of the integrated rate expression for a decomposition first-order reaction?

A)
B)
C)
D)
E)

Question 28

For a certain reaction of the general form aA $\to$ products,the experimental data plotted as [A] versus time is linear.The slope of this plot must equal

A) -1.
B) the negative of the rate constant.
C) one over the rate constant.
D) the rate constant.
E) 1.

Question 29

The reaction of NO and O₂ produces NO₂.
2 NO(g)+ O₂(g) $\to$ 2 NO₂(g)
The reaction is second-order with respect to NO(g)and first-order with respect to O₂(g).At a given temperature,the rate constant,k,equals 4.7 $\times$ 10² M^-2s^-1.What is the rate of reaction when the initial concentrations of NO and O₂ are 0.025 M and 0.015 M,respectively?

A) 2.6 $\times$ 10^-3 M/s
B) 4.4 $\times$ 10^-3 M/s
C) 0.18 M/s
D) 2.0 $\times$ 10^-8 M/s
E) 3.8 $\times$ 10² M/s

Question 30

For the reaction 2A + B $\to$ C,the rate law is
.
Which of the factor(s)will affect the value of the $\underline{\text{ rate constant }}$ for this reaction?
1)decreasing the temperature
2)adding a catalyst
3)decreasing the concentration of reactant A

A) 1 only
B) 2 only
C) 3 only
D) 1 and 2
E) 2 and 3

Question 31

At a given temperature,a first-order reaction has a rate constant of 3.5 $\times$ 10^-3 s^-1.How long will it take for the reaction to be 24% complete?

A) 410 s
B) 1200 s
C) 910 s
D) 34 s
E) 78 s

Question 32

A student analyzed a first-order reaction and obtained the graph below.Unfortunately,the student forgot to label the axes.What are the correct labels for the x and y axes?

A) x axis = time,y axis = ln[A]
B) x axis = ln[time] ,y axis = [A]
C) x axis = ln[time],y axis = [A]
D) x axis = time,y axis = 1/[A]
E) x axis = 1/time,y axis = 1/[A]

Question 33

The rate constant for a particular reaction is 0.0040 M.s^-1.What is the overall order of this reaction?

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

Question 34

The reaction A $\to$ B follows first-order kinetics with a half-life of 21.7 hours.If the concentration of A is 0.023 M after 48.0 hours,what is the initial concentration of A?

A) 0.0050 M
B) 0.051 M
C) 0.51 M
D) 0.11 M
E) 2.0 $\times$ 10² M

Question 35

Which of the following statements is correct for the first-order reaction: A $\to$ 2B?

A) The concentration of A decreases linearly with respect to time.
B) The concentration of A is constant with respect to time.
C) The natural logarithm of the concentration of A decreases linearly with respect to time.
D) The rate of reaction is constant with respect to time.
E) The rate constant,k,of the reaction decreases linearly with respect to time.

Question 36

A first-order chemical reaction is observed to have a rate constant of 34 min^-1.What is the corresponding half-life for the reaction?

A) 1.2 s
B) 1.2 min
C) 49 min
D) 1.8 s
E) 48.6 s

Question 37

For which of the following hypothetical rate laws would the units of the rate constant have the general form M^-2.h^-1?

A) rate = k[A]³
B) rate = k[A]²
C) rate = k[A]
D) rate = k
E) rate = k[A]⁴

Question 38

The rate constant of a first-order decomposition reaction is 0.0147 s^-1.If the initial concentration of reactant is 0.178 M,what is the concentration of reactant after 30.0 seconds?

A) 8.72 $\times$ 10⁵ M
B) 0.0645 M
C) 0.115 M
D) 0.0785 M
E) 0.643 M

Question 39

For the reaction A + 2B $\to$ C,the rate law is
.
What are the units of the rate constant where time is measured in seconds?

A)
B)
C)
D)
E)

Question 40

For a certain reaction of the general form aA $\to$ products,a plot of the experimental data as 1/[A] versus time is linear.What is the reaction order with respect to reactant A?

A) zero
B) first
C) second
D) third
E) fourth

Question 41

The rate constant at 366 K for a first-order reaction is 7.7 $\times$ 10^-3 s^-1 and the activation energy is 15.9 kJ/mol.What is the value of the frequency factor,A,in the Arrhenius equation? (R = 8.314 J/K.mol)

A) 0.0047 s^-1
B) 0.70 s^-1
C) 0.93 s^-1
D) 1.1 s^-1
E) 1.4 s^-1

Question 42

The Arrhenius equation, expresses the dependence of the rate constant on the reaction temperature.The slope of a plot of ln(k)versus 1/T is equal to

A)
B)
C)
D)
E)

Question 43

For the hypothetical reaction aA $\to$ products,the experimental data showed the following behavior (below).What is the reaction order with respect to reactant A?

A) zero order
B) first order
C) second order
D) third order
E) fourth order

Question 44

For a chemical reaction,the activation energy for the forward reaction is +181 kJ and the activation energy for the backward reaction is +62 kJ.What is the overall energy change for the forward reaction?

A) -119 kJ
B) -62 kJ
C) +119 kJ
D) +181 kJ
E) +243 kJ

Question 45

The decomposition of formic acid follows first-order kinetics.
HCO₂H(g) $\to$ CO₂(g)+ H₂(g)
The half-life for the reaction at 550 ^$\circ$ C is 24 seconds.How many seconds does it take for the formic acid concentration to decrease by 87.5%?

A) 24 s
B) 36 s
C) 48 s
D) 72 s
E) 96 s

Question 46

Molecules must overcome a barrier called the activation energy if they are to react.The highest energy point reached during the progress of a reaction is called the ____.

A) rate determining step
B) transition state
C) half-life
D) elementary step
E) intermediate state

Question 47

For the formation of 1 mol of nitrosyl chloride at a given temperature, $\Delta$ _rH = -36 kJ/mol.
NO(g)+ ½ Cl₂(g) $\to$ NOCl(g)
The activation energy for this reaction is 67 kJ/mol.What is the activation energy for the reverse reaction?

A) 67 kJ/mol
B) 31 kJ/mol
C) 103 kJ/mol
D) -36 kJ/mol
E) -103 kJ/mol

Question 48

The decomposition of phosphine,PH₃,follows first-order kinetics.
4 PH₃(g) $\to$ P₄(g)+ 6 H₂(g)
The half-life for the reaction at 550 ^$\circ$ C is 81.3 seconds.What percentage of phosphine remains after 195 seconds?

A) 2.2%
B) 9.8%
C) 19%
D) 42%
E) 58%

Question 49

A second-order reaction starts with an initial concentration of 0.100 mol/L of the reactant.If the rate constant is 1.4 $\times$ 10^-2 L/mol·s,what is the time required to decrease the initial concentration to 0.050 mol/L?
2A $\to$ B $~~~~~~~~$ rate = k[A]²

A) 710 s
B) 1100 s
C) 49.5 s
D) 3.57 s
E) 2100 s

Question 50

For the zero-order reaction below,a graph of ____ versus time will generate a straight line.
A $\to$ B + C $~~~~~~~~$ rate = k[A]⁰

A) [A]_t
B)
C) ln[A]_t
D)
E)

Question 51

In general,as temperature increases,the rate of a chemical reaction

A) decreases due to fewer collisions with proper molecular orientation.
B) increases for exothermic reactions,but decreases for endothermic reactions.
C) increases due to a greater number of effective collisions.
D) remains unchanged.
E) decreases due to an increase in the activation energy.

Question 52

Calculate the activation energy,E_a,for
N₂O₅(g) $\to$ 2 NO₂(g)+ 1/2 O₂(g)
Given k (at 45.0 ^$\circ$ C)= 5.79 $\times$ 10^-4 s^-1 and k (at 60.0 ^$\circ$ C)= 3.83 $\times$ 10^-3 s^-1.(R = 8.314 J/K.mol)

A) 0.256 kJ/mol
B) 2.83 kJ/mol
C) 31.1 kJ/mol
D) 111 kJ/mol
E) 389 kJ/mol

Question 53

Hydrogen peroxide decomposes into water and oxygen in a first-order process.H₂O₂(aq) $\to$ H₂O( )+ 1/2 O₂(g)
At 20.0 ^$\circ$ C,the half-life for the reaction is 3.92 $\times$ 10⁴ seconds.If the initial concentration of hydrogen peroxide is 0.52 M,what is the concentration after 7.00 days?

A) 1.2 $\times$ 10^-5 M
B) 0.034 M
C) 0.074 M
D) 0.22 M
E) 0.52 M

Question 54

For the second-order reaction below,the initial concentration of reactant A is 0.24 M.If the rate constant for the reaction is 1.5 $\times$ 10^-2 M^-1s^-1,what is the concentration of A after 265 seconds?
2A $\to$ B + C $~~~~~~~~$ rate = k[A]²

A) 0.12 M
B) 0.19 M
C) 0.95 M
D) 4.0 M
E) 5.2 M

Question 55

The rate constant for a first-order reaction is 1.4 $\times$ 10^-2 s^-1 at 716 K and 5.5 $\times$ 10^-2 s^-1 at 864 K.What is the activation energy? (R = 8.314 J/K.mol)

A) 27 kJ/mol
B) 21 kJ/mol
C) 47 kJ/mol
D) 5700 kJ/mol
E) 48 kJ/mol

Question 56

The Arrhenius equation, ,relates the rate constant of reaction and temperature.A plot of ____ versus 1/T will yield a straight line with a slope of -E_a/R.

A) k₂/k₁
B) -E_a
C) ln(k)
D)
E) 1/RT

Question 57

According to collision theory,which condition(s)must be met in order for molecules to react?
1)The reacting molecules must collide with sufficient energy to initiate the process of breaking and forming bonds.
2)A catalyst must be in contact with the reacting molecules for a reaction to occur.
3)The reacting molecules must collide with an orientation that can lead to rearrangement of the atoms.

A) 1 only
B) 2 only
C) 3 only
D) 1 and 2
E) 1 and 3

Question 58

A first-order reaction is 40.0% complete at the end of 23.9 minutes.What is the value of the rate constant?

A) 3.83 $\times$ 10^-2 min^-1
B) 2.14 $\times$ 10^-2 min^-1
C) 26.1 min^-1
D) 46.8 min^-1
E) none of these

Question 59

The rate constant for a reaction at 40.0°C is exactly 6 times that at 20.0°C.Calculate the Arrhenius energy of activation for the reaction.(R = 8.314 J/K.0mol)

A) 6.00 kJ/mol
B) 8.22 kJ/mol
C) 68.3 kJ/mol
D) 14.9 kJ/mol
E) none of these

Question 60

What is the half-life of a first-order reaction if it takes 4.4 $\times$ 10^-2 seconds for the concentration to decrease from 0.50 M to 0.20 M?

A) 2.5 $\times$ 10^-2 s
B) 3.3 $\times$ 10^-2 s
C) 1.6 s
D) 21 s
E) 27 s

Question 61

A possible mechanism for the gas phase reaction of NO and H₂ is as follows:

Which of the following statements concerning this mechanism is not directly supported by the information provided?

A) Step 1 is the rate determining step.
B) N₂O₂ is an intermediate.
C) There is no catalyst in this reaction.
D) The rate expression for step 1 is rate = k[NO]².
E) All steps are bimolecular reactions.

Question 62

Elementary steps in a reaction mechanism often include reaction ________.These (usually)short-lived species,which are at one point produced and then later consumed,do not appear in the overall chemical reaction.

Question 63

In a reaction coordinate diagram,reacting molecules are most unstable ______.

A) at their initial position
B) when they are about to collide
C) right after they collide
D) at the transition state

Question 64

Nitrogen dioxide reacts with carbon monoxide to produce nitrogen monoxide and carbon dioxide.
NO₂(g)+ CO(g) $\to$ NO(g)+ CO₂(g)
A proposed mechanism for this reaction is

What is a rate law that is consistent with the proposed mechanism?

A) rate = k[NO₂]²[CO] [NO]^-1
B) rate = k[NO₂]²[CO]
C) rate = k[NO₂][CO]
D) rate = k[NO₃][CO]
E) rate = k[NO₂]²

Question 65

If a catalyst is present in a different phase from the reactants and products,it is referred to as a(n)________ catalyst.

Question 66

The pre-exponential,A,in the Arrhenius equation is called the ________ factor.

Question 67

For the overall reaction
2A + B $\to$ C
Which of the following mechanisms is/are consistent with a rate equation of rate = k[A]²[B]?

A)

B)

C)

D)
E) Answers a and d are both correct.

Question 68

A suggested mechanism for the decomposition of ozone is as follows:

What is the rate law predicted by this mechanism?

A) Rate =
B) Rate = k₂[O] [O₃]
C) Rate =
D) Rate =
E) Rate =

Question 69

Radioactive isotopes decay by ________-order kinetics.

Question 70

The reaction,A + 2B $\to$ B₂ + A,proceeds by the following mechanism: (A is a catalyst.)
A + B $\to$ AB $~~~~~~~~$ $~~~~~~~~$ (slow)
AB + B $\to$ B₂ + A $~~~~~~~~~~$ (fast)
What is the rate law expression for this reaction?

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

Question 71

The ________ of an elementary step is defined as the number of reactant molecules that come together in the reaction.

Question 72

How many mechanistic steps are depicted by in this potential energy diagram?

A) one step
B) two steps
C) three steps
D) four steps
E) five steps

Question 73

Below is a proposed mechanism for the decomposition of H₂O₂.
H₂O₂ + I^- $\to$ H₂O + IO^- $~~~~~~~~$ $~~~~~~~~$ slow

H₂O₂ + IO^- $\to$ H₂O + O₂ + I^- $~~~~~~~~$ $~ ~$ Fast
Which of the following statements is $\underline{\text{ incorrect? }}$

A) IO^- is a catalyst.
B) I^- is a catalyst.
C) The net reaction is 2H₂O₂ $\to$ 2H₂O + O₂.
D) The reaction is first-order with respect to [I^-].
E) The reaction is first-order with respect to [H₂O₂].

Question 74

The mechanism of a chemical reaction is given below.
(CH₃)₃CCl $\to$ (CH₃)₃C⁺ + Cl^- $~~~~~~~~$ $~~~~~~~~$ (slow)
(CH₃)₃C⁺ + OH^- $\to$ (CH₃)₃COH $~~~~ ~~$ $~~~~~~~~$ (fast)
Which of the following statements concerning the reaction is/are CORRECT?
1)The overall balanced reaction is: (CH₃)₃CCl + OH^- $\to$ (CH₃)₃COH + Cl^-
2)Hydroxide ion is a reaction intermediate.
3)The following rate law is consistent with the mechanism: rate = k[(CH₃)₃CCl]OH^-].

A) 1 only
B) 2 only
C) 3 only
D) 1 and 3
E) 1,2,and 3

Question 75

The elementary steps for the catalyzed decomposition of dinitrogen monoxide are shown below.
N₂O(g)+ NO(g) $\to$ N₂(g)+ NO₂(g)
NO₂(g) $\to$ NO(g)+ 1/2 O₂(g)
Which of the following statements is/are CORRECT?
1)The overall balanced reaction is N₂O(g) $\to$ N₂(g)+ 1/2 O₂(g).
2)NO₂(g)is a catalyst for the reaction.
3)NO(g)is a reaction intermediate.

A) 1 only
B) 2 only
C) 3 only
D) 1 and 3
E) 1,2,and 3

Question 76

A catalyst ____.

A) is used up in a chemical reaction
B) changes the potential energy change of the reaction
C) is always a solid
D) does not influence the reaction in any way
E) changes the activation energy of the reaction

Question 77

The effect of adding a catalyst to a reaction is to

A) increase the number of collisions between reactants.
B) lower the activation energy of a reaction.
C) increase the equilibrium constant of a reaction.
D) decrease the yield of the products.
E) increase the enthalpy change of a reaction.

Question 78

For the overall reaction
A + 2B $\to$ C
Which of the following mechanisms yields the correct overall chemical equation and is consistent with the rate equation below?
Rate = k[A][B]

A)

B)

C)

D)

E)

Question 79

Consider the following proposed mechanism.If this mechanism for the overall reaction were correct,and if k₁ were much less than k₂,then the observed rate law would be

A) rate = k₁[A]
B) rate = k₂[I][B]
C) rate = k₁[A]²
D) rate = k₁[A]² - k₂[C][D]
E) rate = k₁k₂[A]²[I][B]

Question 80

The reaction kinetics for a certain reaction are studied over several temperatures.Which of the following is/are $\underline{\text{not }}$ effected by a change in reaction temperature?

A) the reaction rate
B) the rate constant,k
C) the energy of activation,E_a
D) a and b
E) a,b,and c