08 Reaction Kinetics, Set A To print: Ctrl + P, paper A4, margins Default.

Learners' AlleyDesigned by Khow Willard

08

Reaction Kinetics

Set AFoundations

Name

Time 1 hour

Total 33 marks

A Data Booklet may be used.

A

From the lesson

10 marks

1

In 2N₂O₅ → 4NO₂ + O₂, N₂O₅ is used up at 2.0 × 10⁻⁴ mol dm⁻³ s⁻¹. At what rate does NO₂ form?

[1]

Source: Learners' Alley, Reaction Kinetics slides

2

rate = k[NO]²[H₂], with rate in mol dm⁻³ min⁻¹. Find the units of k.

[1]

Source: Learners' Alley, Reaction Kinetics slides

3

CommonFor A + B → C, find the order with respect to A and B, and the rate equation.

expt	[A] / mol dm⁻³	[B] / mol dm⁻³	initial rate / mol dm⁻³ s⁻¹
1	0.10	0.10	2.0 × 10⁻³
2	0.20	0.10	2.0 × 10⁻³
3	0.10	0.30	1.8 × 10⁻²

[3]

Source: Learners' Alley, Reaction Kinetics slides

4

CommonExplain why increasing temperature increases rate.

[2]

Source: Learners' Alley, Reaction Kinetics slides

5

Define order of reaction with respect to a reactant.

[1]

Source: Learners' Alley, Reaction Kinetics slides

6

A first-order reaction has t_½ = 20 s. Find k.

[1]

Source: Learners' Alley, Reaction Kinetics slides

7

What is a homogeneous catalyst?

[1]

Source: Learners' Alley, Reaction Kinetics slides

B

Practice

23 marks

8

CommonTwo colourless substances, X and Y, react to give a coloured substance Z. The time, t, taken for various initial concentrations of X and Y to produce Z is recorded in the table.

[X] / mol dm⁻³	[Y] / mol dm⁻³	t / s
0.05	0.05	44
0.05	0.10	22
0.10	0.05	44

What is the rate equation?

Arate = k[Y]

Brate = k[X][Y]

Crate = k[Y]²

Drate = k[X][Y]²

Answer [1]

Source: HCI 2007 Prelim P1 Q9, via EJC 2022 JC1 Reaction Kinetics Tutorial, A4

9

Propanone reacts with bromine in the presence of an acid catalyst. CH₃COCH₃ + Br₂ → CH₃COCH₂Br + H⁺ + Br⁻

The progress of the reaction was studied by finding the time taken for Br₂ to decolourise using different volumes of reactants.

expt	volume of Br₂ added / cm³	volume of CH₃COCH₃ added / cm³	volume of H⁺ added / cm³	volume of H₂O added / cm³	relative rate
1	10	20	10	10	2
2	10	10	10	20	1
3	10	20	5	15	1
4	10	40	20	30	2

What is the rate equation for the reaction?

Arate = k[CH₃COCH₃][H⁺]

Brate = k[Br₂][H⁺]

Crate = k[CH₃COCH₃][Br₂]

Drate = k[CH₃COCH₃][Br₂][H⁺]

Answer [1]

Source: EJC 2018 Promo, via EJC 2022 Reaction Kinetics Topical Revision, Q7

10

CommonAt 700 °C, nitrogen monoxide and hydrogen react as follows. 2NO(g) + 2H₂(g) → N₂(g) + 2H₂O(g)

expt	initial [NO] / mol dm⁻³	initial [H₂] / mol dm⁻³	initial rate / mol dm⁻³ s⁻¹
1	0.0020	0.012	0.0033
2	0.0040	0.012	0.013
3	0.0060	0.012	0.030
4	0.012	0.0020	0.020
5	0.012	0.0040	0.040
6	0.012	0.0060	0.060

(a)

Use the data to determine the order of the reaction with respect to nitrogen monoxide and with respect to hydrogen.

[2]

(b)

Use these answers to write a rate equation for the reaction. Determine a value for k, stating the units.

[2]

Source: EJC 2022 JC1 Reaction Kinetics Tutorial, A5

11

The reaction between nitric oxide and oxygen is third order overall, and it has been suggested that the mechanism involves the following two steps. 2NO → N₂O₂ (fast) N₂O₂ + O₂ → 2NO₂ (slow)

(a)(i)

Construct a rate equation for this reaction.

[1]

(ii)

Explain the meaning of the terms rate constant, order of reaction and rate-determining step.

[3]

(b)(i)

The decomposition of hydrogen peroxide, H₂O₂ → H₂O + ½O₂, is a first order reaction. Both platinum and the enzyme catalase act as catalysts. Describe how the activation energy is affected by the presence of a catalyst, and explain how this increases the rate.

[2]

(ii)

What effect will the presence of the catalyst have on the rate constant for this reaction? Explain your answer.

[1]

Source: A Level 2005 P3 Q1, via EJC 2022 JC1 Reaction Kinetics Tutorial, A11

12

The rate equation for the reaction 3A(g) + B(g) → C(g) + D(g) is rate = k[A]²[B]. The rate is R for certain pressures of A and B, at constant temperature. Write down, in terms of R, the rate of reaction when

(a)

the partial pressures of both A and B are doubled

[1]

(b)

the partial pressure of A doubles, but that of B remains constant

[1]

(c)

the volume of the reacting vessel is doubled

[1]

(d)

the total pressure is doubled by pumping an inert gas into the system

[1]

Source: RJC H2 Chemistry Tutorial 6 (Reaction Kinetics), Self-check Q4

13

ChallengeSucrose is hydrolysed to glucose and fructose: C₁₂H₂₂O₁₁ + H₂O → C₆H₁₂O₆ + C₆H₁₂O₆. The reaction can be catalysed by dilute acid. The following results were obtained using hydrochloric acid as the catalyst.

expt	initial [HCl] / mol dm⁻³	initial [sucrose] / mol dm⁻³	initial rate / mol dm⁻³ s⁻¹
I	0.10	0.10	0.024
II	0.10	0.15	0.036
III	0.20	0.10	0.048
IV	0.25	y	0.048

(a)

Deduce the order of reaction with respect to both HCl and sucrose. Hence, calculate the rate constant for the reaction, stating the units.

[3]

(b)

Calculate the value of y.

[1]

(c)

The half-life of sucrose in experiment I was 3.0 s. Predict the half-life of sucrose in experiment II and in experiment III, giving your reasoning.

[2]

Source: RJC H2 Chemistry Tutorial 6 (Reaction Kinetics), Standard Q1