Dynamic equilibrium and Le Chatelier's principleAQA A-Level Chemistry: Mind map

Exam questions on Dynamic equilibrium and Le Chatelier's principle

1. Cobalt(II) ions in aqueous solution take part in the equilibrium [Co(H₂O)₆]²⁺(aq) + 4Cl⁻(aq) ⇌ [CoCl₄]²⁻(aq) + 6H₂O(l). The [Co(H₂O)₆]²⁺ ion is pink and the [CoCl₄]²⁻ ion is blue, and the forward reaction is endothermic. A student prepares a purple mixture of the two ions in a sealed tube and leaves it at constant temperature.
   The purple mixture turns blue when it is heated. Explain this observation.2 marks
2. Ammonia is manufactured by the Haber process: N₂(g) + 3H₂(g) ⇌ 2NH₃(g), ΔH = −92 kJ mol⁻¹. The process uses an iron catalyst at a temperature of about 450 °C and a pressure of about 20 MPa.
   Explain why a compromise temperature of about 450 °C is used rather than a much lower temperature.2 marks
3. In the Contact process, sulfur dioxide is oxidised to sulfur trioxide: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g), ΔH = −196 kJ mol⁻¹. A vanadium(V) oxide catalyst is used at about 450 °C and a pressure of about 200 kPa. Under these conditions about 99% of the sulfur dioxide is converted into sulfur trioxide.
   Predict and explain the effect of increasing the temperature on the equilibrium yield of sulfur trioxide.3 marks