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CAIE AS Chemistry 8 Reaction Kinetics

Practise measuring reaction rates and explaining how collision frequency, activation energy and catalysts affect them, then interpret experimental data and reaction pathway…

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Covered syllabus points

8.1 Rate of reaction8.2 Temperature, rate and activation energy8.3 Homogeneous and heterogeneous catalysts

8. Reaction kinetics question 1

[Maximum number: 5]

A large excess of 2-bromo-2-methylpropane is added to 0.0010 mol of NaOH(aq), which contains a few drops of phenolphthalein indicator. A stopwatch is started as soon as the substances are mixed. The time taken for the pink colour to disappear is recorded.

The experiment is repeated at different temperatures, keeping all concentrations and volumes of reagents constant.

Table for Question 8. Reaction kinetics question 1 — CAIE A-Level Chemistry AS

Question (a)

(a)

Explain what is meant by the term rate of reaction.

[ 1 ]

Question (b)

(b)

The graph shows the energy distribution of molecules in a sample of 2-bromo-2-methylpropane at 25∘C25^{\circ} \mathrm{C}.
EaE_{\mathrm{a}} represents the activation energy for the reaction.

Figure for Question (b) — CAIE A-Level Chemistry AS
[ 4 ]

Question (i)

(i)

Label the graph to show the proportion of 2-bromo-2-methylpropane molecules which have sufficient energy to react.

[ 1 ]

Question (ii)

(ii)

Use the same axes to sketch the distribution of energies of molecules in a sample of 2-bromo-2-methylpropane at 50∘C50^{\circ} \mathrm{C}.

[ 2 ]

Question (iii)

(iii)

State the effect of an increase in temperature on EaE_{\mathrm{a}} for this reaction.

[ 1 ]

8. Reaction kinetics question 2

[Maximum number: 2]

Hydrogen halides are compounds formed when halogens (Group 17 elements) react with hydrogen. The bond polarity of the hydrogen halides decreases from HF to HI.

Some relevant data are shown in the table.

Table for Question 8. Reaction kinetics question 2 — CAIE A-Level Chemistry AS

Hydrogen chloride undergoes a reversible reaction with oxygen.

4HCl( g)+O2( g)⇌2Cl2( g)+2H2O( g)4 \mathrm{HCl}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g}) \rightleftharpoons 2 \mathrm{Cl}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{~g})

The reaction is carried out at 400∘C400^{\circ} \mathrm{C} in the presence of a copper(II) chloride catalyst.

State the type of catalyst used in this reaction. Explain how a catalyst is able to increase the rate of a chemical reaction.

8. Reaction kinetics question 3

[Maximum number: 3]

The reaction between Na2 S2O3(aq)\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}(\mathrm{aq}) and HCl(aq) is monitored at constant temperature.

Na2 S2O3+2HCl→2NaCl+SO2+S+H2O\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}+2 \mathrm{HCl} \rightarrow 2 \mathrm{NaCl}+\mathrm{SO}_{2}+\mathrm{S}+\mathrm{H}_{2} \mathrm{O}

Fig. 4.1 shows how the concentration of HCl(aq) varies with time.

Fig. 4.1

Fig. 4.1

Question (a)

(a)

Use Fig. 4.1 to find the average rate of change of concentration of HCl(aq) in this reaction between 0-100 seconds and between 400-500 seconds. Include units in your answers.

0-100 seconds units

400-500 seconds units
[2]

[ 2 ]

Question (b)

(b)

Explain why the rate of reaction changes with time.

[ 1 ]
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