CatalystsEdexcel A-Level Chemistry: Flashcards

Exam questions on Catalysts

1. Ammonia is made industrially by the Haber process, in which nitrogen and hydrogen gases pass over a solid iron catalyst: N₂(g) + 3H₂(g) → 2NH₃(g).
   Describe how a solid catalyst such as iron provides a surface for the reaction of gaseous reactants.2 marks
2. A reaction A → B has an enthalpy change of −60 kJ mol⁻¹ and, uncatalysed, an activation energy of 120 kJ mol⁻¹. When a solid catalyst is used the activation energy falls to 70 kJ mol⁻¹.
   Describe how the reaction profile for the catalysed reaction differs from the uncatalysed reaction, and state what is the same in the two.2 marks
3. In the Contact process, sulfur dioxide and oxygen gases pass over a solid vanadium(V) oxide catalyst at about 700 K: 2SO₂(g) + O₂(g) → 2SO₃(g), ΔH = −196 kJ mol⁻¹. In a simplified model the uncatalysed reaction has an activation energy of 250 kJ mol⁻¹ and the catalysed reaction has an activation energy of 100 kJ mol⁻¹.
   Explain how a solid catalyst speeds up the reaction between two gases, and why the catalyst is used as small pellets or spread over a support.3 marks