DP IB Chemistry: HL

Topic Questions

IBChemistry: HLDPTopic Questions16. Chemical Kinetics (HL only)16.1 Rate Expression & Reaction Mechanism

Syllabus Edition

First teaching 2014

Last exams 2024

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16.1 Rate Expression & Reaction Mechanism

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1
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Which of the following statements about the rate-determining step are correct?

  1. It has the highest activation energy
  2. It can be used to deduce the rate expression
  3. It is the slowest step in the reaction mechanism

  • I and II only 

  • I and III only 

  • II and III only

  • I, II and III

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2
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The rate information below was obtained for the following reaction at a constant temperature: 

A + 2B → C + 2D

Experiment 

Initial [A] 
/ mol dm–3

Initial [B] 
/ mol dm–3

Initial rate
/ mol dm–3 s–1

1

0.25

0.25

3.5 x 10-4

2

0.25

0.50

To be calculated

The rate equation for this reaction is rate = k [B]

What is the initial rate of reaction for experiment 2, in mol dm–3 s–1?

  • (4 x 3.5 x 10-4) 

  • (2 x 3.5 x 10-4) 

  • 3.5 x 10-4 

  • (0.5 x 3.5 x 10-4)

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3
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The rate equation for the reaction between A and B is:

Rate = k [A] [B]

What are the correct units for the rate constant of this rate equation?

  • mol-1 dm3 s-1

  • mol−2 dm6 s−1

  • mol2 dm−6 s−1

  • mol dm-3 s-1

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4
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The rate information below was obtained for the following reaction at a constant temperature: 

5Br– (aq) + BrO3– (aq) + 6H+ (aq) → 3Br2 (aq) + 3H2O (l)

conc-v-rate-graph-

What is the order of reaction with respect to [H+]?

  • One

  • Two

  • Six

  • Zero

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5
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The mechanism for the following reaction between nitrogen(II) oxide and carbon monoxide is shown.

NO2 (g) + CO (g) → NO (g) + CO2 (g)

 

Step 1:   NO2 + NO2 → NO3 + NO   slow step

Step 2:   NO3 + CO → NO2 + CO2   fast step

What rate expression is consistent with the mechanism?

  • Rate = k [NO2] [CO]

  • Rate = k [NO3] [CO]

  • Rate = k [NO2]2

  • Rate = k [NO2]

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1
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The potential energy level profile for the hydrolysis of a tertiary halogenoalkane is shown.

energy-level-profile---tertiary-halogenoalkane-hydrolysis-

Which of the following conclusions can be deduced from the potential energy level profile?

  1. The reaction proceeds via an SN1 mechanism 
  2. The reactants are more stable than the products
  3. The rate-determining step is the first step of the reaction mechanism

  • I and II only 

  • I and III only 

  • II and III only

  • I, II and III

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2
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The rate information below was obtained for the following fourth order reaction at a constant temperature: 

5Br– (aq) + BrO3– (aq) + 6H+ (aq) → 3Br2 (aq) + 3H2O (l)

conc-v-rate-graph- time-v-conc-graph-bromide-ions

Which rate expression is consistent with the data?

  • Rate = k [Br-] [BrO3-] [H+]

  • Rate = k [Br-]2 [H+]2

  • Rate = k [Br-] [BrO3-] [H+]2

  • Rate = k [Br-]2 [BrO3-] [H+]

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3
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The rate information below was obtained for the following reaction at a constant temperature: 

C2H5Br (aq) + OH– (aq) → C2H5OH (aq) + Br– (aq)

[C2H5Br] / mol dm-3

[OH-] / mol dm-3 

Rate / mol dm-3 s-1

2.0 x 10-3

1.0 x 10-2

4.0 x 10-4 

4.0 x 10-3

1.0 x 10-2

8.0 x 10-4 

8.0 x 10-3

2.0 x 10-2

3.2 x 10-3 


What is the correct equation to calculate the value of the rate constant, k?

  • fraction numerator rate over denominator left square bracket straight C subscript 2 straight H subscript 5 Br right square bracket space left square bracket OH to the power of minus right square bracket end fraction

  • fraction numerator left square bracket straight C subscript 2 straight H subscript 5 Br right square bracket space left square bracket OH to the power of minus right square bracket over denominator rate end fraction

  • fraction numerator rate over denominator left square bracket straight C subscript 2 straight H subscript 5 Br right square bracket space left square bracket OH to the power of minus right square bracket squared end fraction

  • fraction numerator rate over denominator left square bracket straight C subscript 2 straight H subscript 5 Br right square bracket squared space left square bracket OH to the power of minus right square bracket squared end fraction

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4
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The mechanism for the following reaction between nitrogen(II) oxide and carbon monoxide is shown.

NO2 (g) + CO (g) → NO (g) + CO2 (g)

 

      Step 1:   NO2 + NO2 ⇌ N2O4   fast step

      Step 2:   N2O4 + 2CO → 2NO + 2CO2   slow step

Which rate expression is consistent with the mechanism?

  • Rate = k [NO2] [CO]2

  • Rate = k [N2O4] [CO]2

  • Rate = k [NO2]2 [CO]2

  • Rate = k [N2O4] [CO]

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5
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The rate information below was obtained for the following reaction of aqueous solutions of F and G, in the presence of a homogeneous catalyst, H, 

2F + 3G → J + 2K

When the concentrations of F and G are doubled, the rate of reaction increases by a factor of four.

When the concentrations of F and H are doubled, the rate of reaction increases by a factor of eight.

Which rate expression is consistent with the data?

  • Rate = k [F]2 [G]3

  • Rate = k [F]2 [H]

  • Rate = k [F] [G] [H]

  • Rate = k [F]2 [H]2

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11 mark

Which of the following statements about the rate constant, k, are correct? 

  1.   High values of k are associated with fast reactions
  2.   The rate constant is affected by temperature
  3.   The units of k are independent of the orders of reaction

  • I and II only

  • I and III only

  • II and III only

  • I, II and III

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21 mark

A student experimentally determined the rate expression for the reaction between iodine and propanone to be: 

Rate = k [H+] [C3H6O] 

Which graph is consistent with this information?

q2_16-1_-medium-rate-expression--reaction-mechanism_ib_hl

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31 mark

The rate information below was obtained for the following reaction at a constant temperature: 

C2H5Br (aq) + OH- (aq) → C2H5OH (aq) + Br - (aq)

[C2H5Br] / mol dm-3

[OH-] / mol dm-3

Rate / mol dm-3 s-1

3.0 x 10-3

2.0 x 10-2

4.0 x 10-4

6.0 x 10-3

2.0 x 10-2

8.0 x 10-4

6.0 x 10-3

4.0 x 10-2

1.6 x 10-3

What are the orders of reaction with respect to C2H5Br and OH-?

  • C2H5Br is first order and OH- is first order 

  • C2H5Br is first order and OH- is second order

  • C2H5Br is second order and OH-is first order

  • C2H5Br is second order and OH- is second order

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41 mark

The mechanism for the following reaction between iodine and propanone is shown. 

CH3COCH3 (aq) + I2 (aq) → CH3COCH2I (aq) + HI (aq)

Step 1: CH3COCH3 + H+ → CH3COH+CH3        

Step 2: CH3COH+CH3 → CH3COHCH2 + H+ 

Step 3: CH3COHCH2 + I2 → CH3COHCH2I + I-

Step 4: CH3COHCH2I → CH3COCH2I + H+ 

Which classifications of CH3COCH3, H+ and CH3COHCH2 are correct?

 

CH3COCH3

H+

CH3COHCH2

A

Intermediate

Intermediate

Catalyst

B

Reactant

Intermediate

Product

C

Reactant

Catalyst

Intermediate

D

Reactant

Product

Intermediate

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51 mark

The proposed mechanism for the following reaction where ethanal dimerises in dilute alkaline solution to form 3-hydroxybutanal is shown. 

2CH3CHO → CH3CH(OH)CH2CHO

Step 1: CH3CHO + :OH- → :CH2CHO + H2O                                       slow step

Step 2: CH3CHO + :CH2CHO → CH3CH(O:-)CH2CHO                        fast step

Step 3: CH3CH(O:-)CH2CHO + H2O → CH3CH(OH)CH2CHO + :OH-  fast step

Which of the following statements is not correct?

  • The rate expression is rate = [CH3CHO] [OH-]

  • Step 1 is the rate-determining step

  • OH- is a catalyst

  • Steps 2 and 3 have a lower activation energy than step 1

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