Dynamic equilibrium and Le Chatelier's principleEdexcel International A Level Chemistry: Flashcards

Exam questions on Dynamic equilibrium and Le Chatelier's principle

1. Dinitrogen tetroxide is a colourless gas that is in equilibrium with brown nitrogen dioxide: N₂O₄(g) ⇌ 2NO₂(g), ΔH = +57 kJ mol⁻¹. A sample of the equilibrium mixture is sealed in a glass tube so that the depth of brown colour can be observed.
   The tube is compressed at constant temperature so that the pressure increases. Predict the change in the position of equilibrium and justify your answer.2 marks
2. Ethanol is manufactured by the reversible reaction of ethene with steam: C₂H₄(g) + H₂O(g) ⇌ C₂H₅OH(g), ΔH = −45 kJ mol⁻¹. The reaction is carried out in a closed reactor at about 570 K and 65 atm using a solid acid catalyst.
   The reactor uses a solid acid catalyst. State and explain the effect of the catalyst on the position of equilibrium and on the time taken to reach equilibrium.2 marks
3. Sulfur trioxide is made in the Contact process by the reversible reaction 2SO₂(g) + O₂(g) ⇌ 2SO₃(g), ΔH = −196 kJ mol⁻¹. The plant uses a vanadium(V) oxide catalyst at about 720 K and a pressure of 1 to 2 atm.
   Explain why a temperature of about 720 K is a compromise for this process.3 marks