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CAIE A-Level Chemistry 7.1.3 Predicting Equilibrium Shifts

Practise predicting qualitative equilibrium changes caused by temperature, concentration, pressure and catalysts.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • use the enthalpy sign to predict the temperature effect and connect the shift to colour, composition or yield
  • compare gaseous mole totals to predict the pressure effect; pressure does not shift equal-mole equilibria
  • state that a catalyst speeds both directions equally and does not change equilibrium position or equilibrium yield

7.1.3—Le Chatelier’s principle to deduce (from question 1

[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 7.1.3—Le Chatelier’s principle to deduce (from question 1 — 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.

The reaction exists in dynamic equilibrium.

The reaction was repeated at 1000∘C1000^{\circ} \mathrm{C} and the same pressure.
State and explain the effect on the composition of the equilibrium mixture of the change in temperature.

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