2.3 Rates of Reaction: Can we control the speed of a reaction?
Recognise chemical change and use collision theory, measurements and catalysts to explain rate.
How to study WJEC GCSE The Sciences
Move from a scientific model to a prediction or method, collect or interpret evidence, show quantitative working and finish with a conclusion whose limits match the data.
Core concepts
Concept 1
Distinguish physical and chemical change and represent conservation of mass.
Exam cue: Identify the unit, entered tier, supplied reference material, command word and relevant scientific enquiry skill.
Concept 2
Select measurements and calculate or compare reaction rates.
Exam cue: Describe what changes on the graph, then explain the change using collision frequency and successful-collision energy.
Concept 3
Explain concentration, pressure, surface area, temperature and catalysts using collision theory.
Exam cue: Use scientific terminology, show quantitative working with units, and connect conclusions to data and the stated model.
Concept 4
Official subtopics: 2.3.1 Chemical changes; 2.3.2 Monitoring the progress of a reaction; 2.3.3 Factors affecting the rate of reaction; 2.3.4 Catalysts.
Concept 5
Scientific enquiry and mathematical skills apply in this topic; bold amplification is Higher Tier only.
Risk pitfalls and guardrails
Saying a catalyst increases product yield or is used up in the reaction.
Guardrail: Do not import outgoing 3430QD content, another science route, a fixed required-practical list or unsupported tier and connection assumptions.
Recalling a fact without applying it to the observation, data, practical method or unfamiliar context.
Guardrail: Use the live secure pack: Task A may use groups of up to three; Task B is individual and highly controlled. Two enquiries are selected by the centre from three.
Importing content, required practicals, tier rules or paper structure from the outgoing WJEC or another awarding-body route.
Guardrail: Bold amplification is Higher-only. Units 1-6 may mix tiers, but Unit 7 is untiered.
Memory anchors
Reaction rate
Change in reactant or product quantity per unit time.
Collision theory
Particles must collide with sufficient energy and suitable orientation to react.
Activation energy
The minimum energy needed for a successful collision.
Catalyst
A substance that increases rate without being used up overall.
Conservation of mass
Atoms are rearranged but not created or destroyed in a reaction.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
What is the mean rate of a reaction? Relate any rate change to measured evidence and successful particle collisions. Compare alternatives under the same stated conditions.
A reaction produces 72 cm³ of gas in 60 s. What is the mean gas-production rate? Relate any rate change to measured evidence and successful particle collisions. Separate the mechanism from the resulting observation.
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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