OCR Gateway GCSE Chemistry A: Monitoring and controlling chemical reactions (C5) overview
An overview of the Monitoring and controlling chemical reactions topic (C5) in OCR Gateway GCSE Chemistry A (J248), mapping rates of reaction and collision theory, measuring and calculating rates, concentration and titrations, reversible reactions and equilibrium, and catalysts and controlling reactions.
Reviewed by: AI editorial process; not yet individually human-reviewed
Jump to a section
Topic C5 Monitoring and controlling chemical reactions of OCR Gateway GCSE Chemistry A (specification J248) is the physical chemistry topic: it covers how fast reactions go, how to measure and calculate rates and concentrations, and how reversible reactions reach equilibrium. It also covers catalysts and how industry controls reactions. This page maps the topic and links to a focused answer page for each part.
The monitoring and controlling topics
- Rates of reaction and collision theory (C5)
- Collision theory, the factors affecting rate (concentration, pressure, surface area, temperature and catalysts), and explaining each in terms of collisions. See Rates of reaction and collision theory.
- Measuring and calculating rates (C5.1)
- Methods for following a reaction, calculating mean rate, interpreting rate graphs, and finding the rate at a moment using a tangent. See Measuring and calculating rates.
- Concentration and titrations (C5.1)
- Concentration in grams and moles per cubic decimetre, the titration method and apparatus, and calculating an unknown concentration from titration results. See Concentration and titrations.
- Reversible reactions and equilibrium (C5.2)
- Reversible reactions, dynamic equilibrium in a closed system, the opposite energy changes, and Le Chatelier's principle for concentration, temperature and pressure. See Reversible reactions and equilibrium.
- Catalysts and controlling reactions (C5.2)
- Catalysts and lowering the activation energy, enzymes as biological catalysts, the effect on reaction profiles, and how conditions are controlled in industry. See Catalysts and controlling reactions.
How this topic is examined
Topic C5 is assessed on Paper 2 (Foundation, J248/02) or Paper 4 (Higher, J248/04), alongside topics C4, C6 and the C7 practical skills, assuming knowledge of C1 to C3. Each paper is 1 hour 45 minutes, worth 90 marks and 50% of the GCSE. Questions include collision-theory explanations, rate and titration calculations, graph work with tangents, and equilibrium predictions. The rates and titration practicals are part of the C7 practical skills.
How to study the monitoring and controlling topic
- Work from the specification statements. Each numbered point is a checklist; questions are written from them.
- Master collision theory. Be able to explain every rate factor in terms of collision frequency and energy.
- Drill the calculations. Mean rate, tangents, concentration and titrations carry many marks; always convert cm3 to dm3.
- Learn equilibrium and Le Chatelier. Know how concentration, temperature and pressure shift an equilibrium.
- Understand catalysts and enzymes. Know how they lower activation energy and why enzymes need an optimum temperature. Use OCR past papers.
For the official specification
OCR publishes the full specification (J248), past papers and mark schemes at ocr.org.uk. Always revise from the current specification and OCR's own past papers, because question style is board-specific.