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CAIE A-Level Chemistry 8.1.3 Calculating Reaction Rates

Practise calculating average reaction rates from concentration, amount or gas-volume data over a stated time interval.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • calculate average rate as change in the specified quantity divided by the elapsed time
  • read two graph coordinates for the stated interval and include the sign only when direction is required
  • convert volume, moles and time units before reporting a rate with a complete compound unit

8.1.3—Experimental data to calculate the rate question 1

[Maximum number: 2]

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

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]

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