CAIE A-Level Chemistry 8.1.2 -

Practise explaining how concentration and pressure change reaction rates through the frequency of effective particle collisions.

Exam points

explain higher concentration or pressure as particles colliding more often
link rate changes during a reaction to falling reactant concentration
compare altered experiments where concentration, temperature or surface area changes

[Maximum number: 1]

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

\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

Explain why the rate of reaction changes with time.

the frequency of effective collisions decreases as concentration of HCl(aq) and/or $\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}$ decreases

All question bank results loaded