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CAIE A-Level Chemistry 8.1 Rate of reaction Question Bank

Practise calculating reaction rates from tables and graphs, then explaining changes using concentration, pressure and collisions.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • calculate average rate from gas volume, concentration change or moles over time
  • explain rate changes using collision frequency and effective collisions
  • interpret rate graphs or tables to compare early and late stages of a reaction

Covered syllabus points

8.1.1—Terms: rate of reaction, frequency of collisions8.1.2—8.1.3—Experimental data to calculate the rate

8.1 Rate of reaction question 1

[Maximum number: 1]

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 8.1 Rate of reaction question 1 — CAIE A-Level Chemistry AS

Explain what is meant by the term rate of reaction.

8.1 Rate of reaction question 2

[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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