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CAIE IGCSE Chemistry 6.3.3 Reversible reaction in a closed system

Practise defining equilibrium in closed systems using reaction rates and concentrations that stop changing macroscopically.

Syllabus
2026–2028
Course
Chemistry 0620

Exam points

  • state that a closed system allows nothing to enter or leave
  • describe equilibrium as equal forward and reverse reaction rates
  • distinguish constant concentrations from reactions having stopped completely

6.3.3—Reversible reaction in a closed system question 1

[Maximum number: 2]

The Periodic Table is a method of classifying elements.

PCl3\mathrm{PCl}_{3} reacts with chlorine, Cl2\mathrm{Cl}_{2}, to form PCl5\mathrm{PCl}_{5}. This reaction is exothermic and reaches an equilibrium.

PCl3( g)+Cl2( g)⇌PCl5( g)\mathrm{PCl}_{3}(\mathrm{~g})+\mathrm{Cl}_{2}(\mathrm{~g}) \rightleftharpoons \mathrm{PCl}_{5}(\mathrm{~g})

Describe two features of an equilibrium.

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