Deck 14: Chemical Kinetics

Question 1

A rate constant with the units L² · mol^-2 · s^-1 is consistent with a

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

Answer 1

third-order reaction.

Question 2

The data below were determined for the reaction shown below. S₂O₈^2- + 3I ^- (aq) $\rarr$ 2SO₄^2- + I₃^- The rate law for this reaction must be:

A)rate = k[S₂O₈^2- ][I ^-]³
B)rate = k[S₂O₈^2-]
C)rate = k[S₂O₈^2-]²[I ^-]²
D)rate = k[I ^-]
E)rate = k[S₂O₈^2-][I ^-]

Answer 2

rate = k[S₂O₈^2-][I ^-]

Question 3

Chlorine dioxide reacts in basic water to form chlorite and chlorate according to the following chemical equation: 2ClO₂(aq)+ 2OH^-(aq) $\rarr$ ClO₂^-(aq)+ ClO₃^-(aq)+ H₂O(l)
A kinetic study of this reaction under a certain set of conditions yielded the data below.

A)rate = k[ClO₂][OH^-]
B)rate = k[ClO₂]²[OH^-]
C)rate = k[ClO₂][OH^-]²
D)rate = k[ClO₂]²[OH^-]²
E)rate = k[ClO₂]⁴[OH^-]

Answer 3

rate = k[ClO₂]²[OH^-]

Question 4

For the hypothetical reaction A + 3B $\rarr$ 2C, the rate of appearance of C given by ( $\Delta$ [C]/ $\Delta$ t)may also be expressed as

A)( $\Delta$ [C]/ $\Delta$ t = $\Delta$ [A]/ $\Delta$ t.)
B)( $\Delta$ [C]/ $\Delta$ t = -(3/2) $\Delta$ [B]/ $\Delta$ t.)
C)( $\Delta$ [C]/ $\Delta$ t = -(2/3) $\Delta$ [B]/ $\Delta$ t.)
D)( $\Delta$ [C]/ $\Delta$ t = -(1/2) $\Delta$ [A]/ $\Delta$ t.)

Question 5

For the reaction BrO₃^- + 5Br^-+ 6H⁺ $\rarr$ 3Br₂ + 3H₂O at a particular time, - $\Delta$ [BrO₃^-]/ $\Delta$ t = 1.5 * 10^-2 M/s. What is - $\Delta$ [Br^-]/ $\Delta$ t at the same instant?

A)13 M/s
B)7.5 * 10^-2 M/s
C)1.5 * 10^-2 M/s
D)3.0 * 10^-3 M/s
E)330 M/s

Question 6

Appropriate units for a first-order rate constant are

A)M/s.
B)1/M·s.
C)1/s.
D)1/M²·s.

Question 7

The reaction A + 2B $\rarr$ products was found to follow the rate law: rate = k[A]²[B]. Predict by what factor the rate of reaction will increase when the concentration of A is doubled, the concentration of B is tripled, and the temperature remains constant.

A)5
B)6
C)12
D)18
E)None of these.

Question 8

For the overall chemical reaction shown below, which one of the following statements can be rightly assumed? 2H₂S(g)+ O₂(g) $\rarr$ 2S(s)+ 2H₂O(l)

A)The reaction is third-order overall.
B)The reaction is second-order overall.
C)The rate law is, rate = k[H₂S]² [O₂].
D)The rate law is, rate = k[H₂S] [O₂].
E)The rate law cannot be determined from the information given.

Question 9

For the following reaction, $\Delta$ P(C₆H₁₄)/ $\Delta$ t was found to be -6.2 * 10^-3 atm/s. C₆H₁₄(g) $\rarr$ C₆H₆(g)+ 4H₂(g)
Determine $\Delta$ P(H₂)/ $\Delta$ t for this reaction at the same time.

A)6.2 * 10^-3 atm/s
B)1.6 * 10^-3 atm/s
C)2.5 * 10^-2 atm/s
D)-1.6 * 10^-3 atm/s
E)-2.5 * 10^-2 atm/s

Question 10

Which one of the following units would not be an acceptable way to express reaction rate?

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

Question 11

Use the following data to determine the rate law for the reaction shown below. 2NO + H₂ $\rarr$ N₂O + H₂O

A)rate = k[NO]
B)rate = k[NO]²
C)rate = k[NO][H₂]
D)rate = k[NO]²[H₂]
E)rate = k[NO]²[H₂]²

Question 12

For the hypothetical reaction A + 3B $\rarr$ 2C, the rate should be expressed as

A)rate = $\Delta$ [A]/ $\Delta$ t.
B)rate = - $\Delta$ [C]/ $\Delta$ t.
C)rate = -3 $\Delta$ [B]/ $\Delta$ t.
D)rate = ¹/₂ $\Delta$ [C]/ $\Delta$ t.
E)rate = ¹/₃ $\Delta$ [B]/ $\Delta$ t.

Question 13

The reaction A + 2B $\rarr$ products has been found to have the rate law, rate = k[A] [B]². While holding the concentration of A constant, the concentration of B is increased from x to 3x. Predict by what factor the rate of reaction increases.

A)3
B)6
C)9
D)27
E)30

Question 14

The reaction A + 2B $\rarr$ products has the rate law, rate = k[A][B]³. If the concentration of B is doubled while that of A is unchanged, by what factor will the rate of reaction increase?

A)2
B)4
C)6
D)8
E)9

Question 15

Chlorine dioxide reacts in basic water to form chlorite and chlorate according to the following chemical equation: 2ClO₂(aq)+ 2OH^-(aq) $\rarr$ ClO₂^-(aq)+ ClO₃^-(aq)+ H₂O(l)
Under a certain set of conditions, the initial rate of disappearance of chlorine dioxide was determined to be 2.30 * 10^-1 M/s. What is the initial rate of appearance of chlorite ion under those same conditions?

A)5.75 x 10^-2 M/s
B)1.15 x 10^-1 M/s
C)2.30 x 10^-1 M/s
D)4.60 x 10^-1 M/s
E)9.20 x 10^-1 M/s

Question 16

It takes 42.0 min for the concentration of a reactant in a first-order reaction to drop from 0.45 M to 0.32 M at 25°C. How long will it take for the reaction to be 90% complete?

A)13.0 min
B)86.0 min
C)137 min
D)222 min
E)284 min

Question 17

For the reaction C₆H₁₄(g) $\rarr$ C₆H₆(g)+ 4H₂(g), $\Delta$ P(H₂)/ $\Delta$ t was found to be 2.5 * 10^-2 atm/s, where $\Delta$ P(H₂)is the change in pressure of hydrogen. Determine $\Delta$ P(C₆H₁₄)/ $\Delta$ t for this reaction at the same time.

A)2.5 * 10^-2 atm/s
B)-6.2 * 10^-3 atm/s
C)-2.5 * 10^-2 atm/s
D)0.10 atm/s
E)6.2 * 10^-3 atm/s

Question 18

A rate constant will have the units mol · L^-1 · s^-1 when the reaction is overall

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

Question 19

Nitric oxide gas (NO)reacts with chlorine gas according to the chemical equation given below. NO + Cl₂ $\rarr$ NOCl
The following initial rates of reaction have been measured for the given reagent concentrations. Which of the following is the rate law (rate equation)for this reaction?

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

Question 20

The reaction A + 2B $\rarr$ products was found to have the rate law, rate = k[A] [B]². Predict by what factor the rate of reaction will increase when the concentration of A is doubled and the concentration of B is also doubled.

A)2
B)4
C)6
D)8
E)9

Question 21

At 700 K, the rate constant for the following reaction is 6.2 *10^-4 min^-1. How many minutes are required for 20% of a sample of cyclopropane to isomerize to propene?

A)1,120 min
B)360 min
C)3710 min
D)1.4 * 10^-4 min
E)280 min

Question 22

The first-order reaction SO₂Cl₂ $\rarr$ SO₂ + Cl₂ is 10% complete in 80. min. How long would it take for the reaction to be 95% complete?

A)1.8 min
B)104 min
C)530 min
D)2300 min
E)990 min

Question 23

The isomerization of cyclopropane to form propene is a first-order reaction. At 760 K, 85% of a sample of cyclopropane changes to propene in 79.0 min. Determine the rate constant for this reaction at 760 K.

A)3.66 * 10^-2 min^-1
B)1.04 * 10^-2 min^-1
C)2.42 min^-1
D)2.06 * 10^-3 min^-1
E)2.40 * 10^-2 min^-1

Question 24

At 25°C, the second-order reaction NOCl(g) $\rarr$ NO(g)+ ¹/₂Cl₂(g) is 50% complete after 5.82 hours when the initial concentration of NOCl is 4.46 mol/L. How long will it take for the reaction to be 75% complete?

A)8.22 hr
B)11.6 hr
C)15.5 hr
D)17.5 hr
E)23.0 hr

Question 25

Appropriate units for a second-order rate constant are

A)M/s.
B)1/M·s.
C)1/s.
D)1/M²·s.

Question 26

A certain first-order reaction A $\rarr$ B is 25% complete in 42 min at 25°C. What is the half-life of the reaction?

A)21 min
B)42 min
C)84 min
D)20 min
E)101 min

Question 27

Ammonium ion (NH₄⁺)reacts with nitrite ion (NO₂^-)to yield nitrogen gas and liquid water. The following initial rates of reaction have been measured for the given reactant concentrations. Which of the following is the rate law (rate equation)for this reaction?

A)rate = k [NH₄⁺] [NO₂^-]⁴
B)rate = k [NH₄⁺] [NO₂^-]
C)rate = k [NH₄⁺] [NO₂^-]²
D)rate = k [NH₄⁺]² [NO₂^-]
E)rate = k [NH₄⁺]^1/2 [NO₂^-]^1/4

Question 28

A certain reaction A $\rarr$ products is second order in A. If this reaction is 10.% complete after 20. s, how long would it take for the reaction to be 90.% complete?

A)180 s
B)1600 s
C)440 s
D)18,000 s
E)540 s

Question 29

The isomerization of cyclopropane to form propene is a first-order reaction. At 760 K, 15% of a sample of cyclopropane changes to propene in 6.8 min. What is the half-life of cyclopropane at 760 K?

A)3.4 * 10^-2 min
B)2.5 min
C)23 min
D)29 min
E)230 min

Question 30

The isomerization of cyclopropane to propene follows first-order kinetics. At 700 K, the rate constant for this reaction is 6.2 * 10^-4 min^-1. How many minutes are required for 10.0% of a sample of cyclopropane to isomerize to propene?

A)16,100 min
B)170 min
C)3,710 min
D)1.43 * 10^-3 min
E)1,120 min

Question 31

A certain reaction A $\rarr$ products is second order in A. If this reaction is 85% complete in 12 minutes, how long would it take for the reaction to be 15% complete?

A)110 s
B)27 s
C)62 s
D)130 s
E)22 s

Question 32

At 25°C the rate constant for the first-order decomposition of a pesticide solution is 6.40 * 10^-3 min^-1. If the starting concentration of pesticide is 0.0314 M, what concentration will remain after 62.0 min at 25°C?

A)1.14 * 10^-1 M
B)47.4 M
C)-8.72.0 M
D)2.11 * 10^-2 M
E)2.68 * 10^-2 M

Question 33

A first-order reaction has a rate constant of 7.5 * 10^-3 /s. The time required for the reaction to be 60% complete is

A)3.8 * 10^-3 s.
B)6.9 * 10^-3 s.
C)68 s.
D)120 s.
E)130 s.

Question 34

A city's water supply is contaminated with a toxin at a concentration of 0.63 mg/L. Fortunately, this toxin decomposes to a safe mixture of products by first-order kinetics with a rate constant of 0.27 day^-1. How long will it take for half of the toxin to decompose?

A)0.17 days
B)0.27 days
C)0.38 days
D)2.3 days
E)2.6 days

Question 35

Nitric oxide reacts with chlorine to form nitrosyl chloride, NOCl. Use the following data to determine the rate equation for the reaction. NO + ¹/₂Cl₂ $\rarr$ NOCl

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

Question 36

The following initial rate data apply to the reaction below. F₂(g)+ 2Cl₂O(g) $\rarr$ 2FClO₂(g)+ Cl₂(g) Which of the following is the rate law (rate equation)for this reaction?

A)rate = k[F₂]²[Cl₂O]⁴
B)rate = k[F₂]²[Cl₂O]
C)rate = k[F₂][Cl₂O]
D)rate = k[F₂][Cl₂O]²
E)rate = k[F₂]²[Cl₂O]²

Question 37

A first-order reaction has a rate constant of 3.00 * 10^-3 s^-1. The time required for the reaction to be 75.0% complete is

A)95.8 s.
B)462 s.
C)231 s.
D)201 s.
E)41.7 s.

Question 38

A city's water supply is contaminated with a toxin at a concentration of 0.63 mg/L. For the water to be safe for drinking, the concentration of this toxin must be below 1.5 * 10^-3 mg/L. Fortunately, this toxin decomposes to a safe mixture of products by first-order kinetics with a rate constant of 0.27 day^-1. How long will it take for the water to be safe to drink?

A)2.2 days
B)2.6 days
C)20. days
D)22 days
E)27 days

Question 39

A certain first-order reaction A $\rarr$ B is 25% complete in 42 min at 25°C. What is its rate constant?

A)6.8 * 10^-3 min^-1
B)8.3 * 10^-3 min^-1
C)3.3 * 10^-2 min^-1
D)-3.3 * 10^-2 min^-1
E)11 min^-1

Question 40

Benzoyl chloride, C₆H₅COCl, reacts with water to form benzoic acid, C₆H₅COOH, and hydrochloric acid. This first-order reaction is 25% complete after 26 s. How much longer would one have to wait in order to obtain 99% conversion of benzoyl chloride to benzoic acid?

A)393 s
B)419 s
C)183 s
D)293 s
E)209 s

Question 41

Which one of the following changes would alter the rate constant (k)for the reaction 2A + B $\rarr$ products?

A)increasing the concentration of A
B)increasing the concentration of B
C)increasing the temperature
D)measuring k again after the reaction has run for a while

Question 42

The graphs below all refer to the same reaction. What is the order of this reaction?

A)zeroth order
B)first order
C)second order
D)unable to predict

Question 43

The thermal decomposition of acetaldehyde, CH₃CHO $\rarr$ CH₄ + CO, is a second-order reaction. The following data were obtained at 518°C. Calculate the rate constant for the decomposition of acetaldehyde from the above data.

A)2.2 * 10^-3/s
B)0.70 mmHg/s
C)2.2 * 10^-3/mmHg·s
D)6.7 * 10^-6/mmHg·s
E)5.2 * 10^-5/mmHg·s

Question 44

At 25°C, by what factor is the reaction rate increased by a catalyst that reduces the activation energy of the reaction by 1.00 kJ/mol?

A)1.63
B)123
C)1.04
D)1.50
E)2.53

Question 45

For the chemical reaction A $\rarr$ C, a plot of 1/[A]_t versus time was found to give a straight line with a positive slope. What is the order of reaction?

A)zeroth
B)first
C)second
D)Such a plot cannot reveal the order of the reaction.

Question 46

The reaction 2NO₂(g) $\rarr$ 2NO(g)+ O₂(g)is suspected to be second order in NO₂. Which of the following kinetic plots would be the most useful to confirm whether or not the reaction is second order?

A)a plot of [NO₂]^-1 vs. t
B)a plot of ln [NO₂] vs. t
C)a plot of [NO₂] vs. t
D)a plot of ln [NO₂]^-1 vs. t
E)a plot of [NO₂]² vs. t

Question 47

The isomerization of methyl isocyanide, CH₃NC $\rarr$ CH₃CN, follows first-order kinetics. The half-lives were found to be 161 min at 199°C and 12.5 min at 230°C. Calculate the activation energy for this reaction.

A)6.17 * 10^-3 kJ/mol
B)31.4 kJ/mol
C)78.2 kJ/mol
D)124 kJ/mol
E)163 kJ/mol

Question 48

The Arrhenius equation is k = Ae^-Ea/RT. The slope of a plot of ln k vs. 1/T is equal to

A)-k.
B)k.
C)E_a.
D)-E_a /R.
E)A.

Question 49

The isomerization of cyclopropane follows first order kinetics. The rate constant at 700 K is 6.20 * 10^-4 min^-1, and the half-life at 760 K is 29.0 min. Calculate the activation energy for this reaction.

A)5.07 kJ/mol
B)27.0 kJ/mol
C)50.7 kJ/mol
D)60. kJ/mol
E)270. kJ/mol

Question 50

The activation energy for the following reaction is 60. kJ/mol. Sn²⁺ + 2Co³⁺ $\rarr$ Sn⁴⁺ + 2Co²⁺
By what factor (how many times)will the rate constant increase when the temperature is raised from 10°C to 28°C?

A)1.002
B)4.6
C)5.6
D)2.8
E)696

Question 51

The thermal decomposition of acetaldehyde, CH₃CHO $\rarr$ CH₄ + CO, is a second-order reaction. The following data were obtained at 518°C. Based on the data given, what is the half-life for the disappearance of acetaldehyde?

A)1.5 * 10⁵ s
B)410 s
C)5.4 * 10⁷ s
D)520 s
E)305 s

Question 52

Calculate the activation energy, in kJ/mol, for the redox reaction Sn²⁺ + 2Co³⁺ $\rarr$ Sn⁴⁺ + 2Co²⁺.

A)59.2
B)0.477
C)5.37
D)163 kJ
E)48.1 kJ

Question 53

At 30°C, by how much is a reaction's activation energy decreased by the addition of a catalyst if the catalyst triples the reaction rate?

A)2.77 kJ/mol
B)274 J/mol
C)2.70 J/mol
D)119 J/mol
E)1.20 kJ/mol

Question 54

For a second order reaction, the half-life is equal to

A)t_1/2 = 0.693/k.
B)t_1/2 = k/0.693.
C)t_1/2 = 1/k[A]_o.
D)t_1/2 = k.
E)t_1/2 = [A]_o/2k.

Question 55

For the chemical reaction A $\rarr$ B + C, a plot of [A]_t versus time is found to give a straight line with a negative slope. What is the order of reaction with respect to A?

A)zeroth
B)first
C)second
D)third
E)Such a plot cannot reveal the order of the reaction.

Question 56

For what order reaction does the half-life get longer as the initial concentration increases?

A)zeroth order
B)first order
C)second order
D)none of them because half-life is always independent of the initial concentration

Question 57

The activation energy for the reaction CH₃CO $\rarr$ CH₃ + CO is 71 kJ/mol. How many times greater is the rate constant for this reaction at 170°C than at 150°C?

A)0.40
B)1.1
C)2.5
D)4.0
E)5.0

Question 58

For the reaction X + Y $\rarr$ Z, the reaction rate is found to depend only upon the concentration of X. A plot of 1/X verses time gives a straight line.
What is the rate law for this reaction?

A)rate = k [X]
B)rate = k [X]²
C)rate = k [X][Y]
D)rate = k [X]²[Y]

Question 59

What is the slope of an Arrhenius plot for the following reaction? 2NOCl $\rarr$ 2NO + Cl₂

A)8.18 * 10^-2 K
B)5.06 * 10^-2 K
C)-1.22 * 10⁴ K
D)-1.96 * 10⁴ K
E)not enough information to calculate the slope

Question 60

If E_a for a certain biological reaction is 50. kJ/mol, by what factor (how many times)will the rate of this reaction increase when body temperature increases from 37°C (normal)to 40°C (fever)?

A)1.15
B)1.20
C)2.0 * 10⁵
D)1.0002
E)2.0

Question 61

The activation energy of a certain uncatalyzed reaction is 64 kJ/mol. In the presence of a catalyst, the E_a is 55 kJ/mol. How many times faster is the catalyzed than the uncatalyzed reaction at 400°C? Assume that the frequency factor remains the same.

A)5.0 times
B)1.16 times
C)15 times
D)2.0 times
E)0.2 times

Question 62

Given that E_a for a certain biological reaction is 48 kJ/mol and that the rate constant is 2.5 * 10^-2 s^-1 at 15°C, what is the rate constant at 37°C?

A)2.7 * 10^-2 s^-1
B)2.5 * 10^-1 s^-1
C)1.0 * 10^-1 s^-1
D)6.0 * 10^-3 s^-1
E)1.1 s^-1

Question 63

Which of the following statements is false?

A)A catalyst increases the rate of the forward reaction, but does not alter the reverse rate.
B)A catalyst alters the mechanism of reaction.
C)A catalyst alters the activation energy.
D)A catalyst may be altered in the reaction, but is always regenerated.
E)A catalyst increases the rate of reaction, but is not consumed.

Question 64

The activation energy for the following first-order reaction is 102 kJ/mol. N₂O₅(g) $\rarr$ 2NO₂(g)+ ¹/₂O₂(g)
The value of the rate constant (k)is 1.35 * 10^-4 s^-1 at 35°C. What is the value of k at 0°C?

A)8.2 * 10^-7 s^-1
B)1.9 * 10^-5 s^-1
C)4.2 * 10^-5 s^-1
D)2.2 * 10^-2 s^-1
E)none of these

Question 65

An increase in the temperature of the reactants causes an increase in the rate of reaction. The best explanation for this behavior is that as the temperature increases,

A)the concentration of reactants increases.
B)the activation energy decreases.
C)the collision frequency increases.
D)the fraction of collisions with total kinetic energy greater than E_a increases.
E)the activation energy increases.

Question 66

Solids cannot react with gases.

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

Question 67

For the chemical reaction system described by the diagram below, which statement is true? If the E_a for the forward reaction is 25 kJ/mol and the enthalpy of reaction is -95 kJ/mol, what is E_a for the reverse reaction?

A)120 kJ/mol
B)70 kJ/mol
C)95 kJ/mol
D)25 kJ/mol
E)-70 kJ/mol

Question 68

Nitrous oxide (N₂O)decomposes at 600°C according to the balanced equation 2N₂O(g) $\rarr$ 2N₂(g)+ O₂(g)
A reaction mechanism involving three steps is shown below. Identify all of the catalysts in the following mechanism.
Cl₂(g) $\rarr$ 2Cl(g)
N₂O(g)+ Cl(g) $\rarr$ N₂(g)+ ClO(g)(occurs twice)
ClO(g)+ ClO(g) $\rarr$ Cl₂(g)+ O₂(g)

A)Cl
B)Cl₂
C)ClO
D)N₂O
E)ClO and Cl

Question 69

The activation energy for the reaction O + O₃ $\rarr$ 2O₂ is 25 kJ/mol, and the enthalpy change is $\Delta$ H = -388 kJ/mol. What is the activation energy for the decomposition of O₂ by the reverse reaction?

A)413 kJ
B)388 kJ
C)363 kJ
D)50 kJ
E)25 kJ

Question 70

With respect to the figure below, which choice correctly identifies all the numbered positions?

A)
B)
C)
D)
E)

Question 71

When the concentrations of reactant molecules are increased, the rate of reaction increases. The best explanation for this phenomenon is that as the reactant concentration increases,

A)the average kinetic energy of molecules increases.
B)the frequency of molecular collisions increases.
C)the rate constant increases.
D)the activation energy increases.
E)the order of reaction increases.

Question 72

The reaction C₄H₁₀ $\rarr$ C₂H₆ + C₂H₄ has an activation energy (E_a)of 350 kJ/mol, and the E_a of the reverse reaction is 260 kJ/mol. Estimate $\Delta$ H, in kJ/mol, for the reaction as written above.

A)-90 kJ/mol
B)+90 kJ/mol
C)350 kJ/mol
D)-610 kJ/mol
E)+610 kJ/mol

Question 73

The rate law for the reaction H₂O₂ + 2H⁺ + 2I ^- $\rarr$ I₂ + 2H₂O is rate = k[H₂O₂][I ^-]. The following mechanism has been suggested. H₂O₂ + I ^- $\rarr$ HOI + OH ^- slow
OH ^- + H⁺ $\rarr$ H₂O fast
HOI + H⁺ + I ^- $\rarr$ I₂ + H₂O fast
Identify all intermediates included in this mechanism.

A)H⁺ and I ^-
B)H⁺ and HOI
C)HOI and OH^-
D)H⁺ only
E)H₂O and OH^-

Question 74

Complete the following statement: A catalyst

A)increases the activation energy.
B)alters the reaction mechanism.
C)increases the average kinetic energy of the reactants.
D)increases the concentration of reactants.
E)increases the collision frequency of reactant molecules.

Question 75

For the reaction X₂ + Y + Z $\rarr$ XY + XZ, it is found that the rate equation is rate = k [X₂][Y]. Why does the concentration of Z have no effect on the rate?

A)The concentration of Z is very small and the others are very large.
B)Z must react in a step after the rate determining step.
C)Z is an intermediate.
D)The fraction of molecules of Z that have very high energies is zero.
E)The activation energy for Z to react is very high.

Question 76

The following reaction in aqueous solution was found to be first order in [OH^-], first order in [C₂H₅Br], and inverse first order in Br^-.
C₂H₅Br + OH^- $\rarr$ C₂H₅OH + Br^-
Which one of the following mechanisms is consistent with the observed reaction order?

A)C₂H₅Br $\rarr$ C₂H₅⁺ + Br^{- -} fast C₂H₅⁺ + OH^- $\rarr$ C₂H₅OH slow
B)C₂H₅Br +H₂O $\rarr$ C₂H₅OH + H⁺ + Br^- slow H⁺ + OH^- $\rarr$ H₂O fast
C)C₂H₅Br $\rarr$ C₂H₅⁺ + Br^- slow C₂H₅⁺ + OH^- $\rarr$ C₂H₅OH fast
D)C₂H₅Br $\rarr$ C₂H₅⁺ + Br^- slow OH^- + Br^- $\rarr$ HOBr fast
HOBr + C₂H₅⁺ $\rarr$ C₂H₅OH + Br^- fast

Question 77

For the chemical reaction system described by the diagram below, which statement is true?

A)The forward reaction is endothermic.
B)The activation energy for the forward reaction is greater than the activation energy for the reverse reaction.
C)At equilibrium, the activation energy for the forward reaction is equal to the activation energy for the reverse reaction.
D)The activation energy for the reverse reaction is greater than the activation energy for the forward reaction.
E)The reverse reaction is exothermic.

Question 78

The gas phase reaction of nitrogen dioxide and carbon monoxide was found by experiment to be second-order with respect to NO₂, and zeroth-order with respect to CO below 25°C. NO₂ + CO $\rarr$ NO + CO₂
Which one of the following mechanisms is consistent with the observed reaction order?

A)NO₂ + 2CO $\rarr$ N + 2CO₂ fast N + NO₂ $\rarr$ 2NO slow
B)NO₂ + 2CO $\rarr$ N + 2CO₂ slow N + NO₂ $\rarr$ 2NO fast
C)NO₂ + NO₂ $\rarr$ NO₃ + NO fast NO₃ + CO $\rarr$ NO₂ + CO₂ slow
D)NO₂ + NO₂ $\rarr$ NO₃ + NO slow NO₃ + CO $\rarr$ NO₂ + CO₂ fast

Question 79

A reaction mechanism usually is

A)the same as the balanced chemical equation.
B)restricted to only one possible explanation.
C)obvious if the reaction order is known.
D)difficult, if not impossible, to prove.
E)obvious if the activation energy is known.

Question 80

The rate law for the reaction 2NO₂ + O₃ $\rarr$ N₂O₅ + O₂ is rate = k[NO₂][O₃]. Which one of the following mechanisms is consistent with this rate law?

A)NO₂ + NO₂ $\rarr$ N₂O₄ (fast) N₂O₄ + O₃ $\rarr$ N₂O₅ + O₂ (slow)
B)NO₂ + O₃ $\rarr$ NO₅ (fast) NO₅ + NO₅ $\rarr$ N₂O₅ + ⁵/₂O₂ (slow)
C)NO₂ + O₃ $\rarr$ NO₃ + O₂ (slow) NO₃ + NO₂ $\rarr$ N₂O₅ (fast)
D)NO₂ + NO₂ $\rarr$ N₂O₂ + O₂ (slow) N₂O₂ + O₃ $\rarr$ N₂O₅ (fast)