Exam Connection (OCR A J248)

Where it appears: Paper 2 (C5 Monitoring and Controlling Chemical Reactions). P3 topic — appears in roughly 1 in 3 sittings, typically 3–6 marks.

Typical question types:

• "State the conditions used in the Haber process" (2–3 marks)
• "Explain why a temperature of 450°C is used rather than a lower temperature" (2 marks — must address both rate AND equilibrium)
• "Explain the effect of increasing pressure on the yield of ammonia" (2 marks)
• "State one use of ammonia" (1 mark)

Key examiner demand: For "explain" questions, you MUST address both rate and yield/equilibrium. Stating only one gets partial credit. The word "compromise" is a useful signpost in your answer.

Edexcel 1CH0: Examined in Paper 2 (1CH0/2). Conditions (450°C, 200 atm, iron catalyst), Le Chatelier's principle applied to both temperature and pressure changes, and the trade-off between rate and yield are all standard Edexcel examination topics. In Edexcel-style questions, the command word "Suggest" appears frequently — use your chemistry knowledge to apply to an unfamiliar context.