1.1Chemical Changes and Structure
Rates of Reaction — SQA National 5 Chemistry — SQA National 5 Chemistry Revision Notes & Topical Questions
5 min read 2 parts Lesson 1 of 4
Section 1 of 2Measuring the rate of a chemical reaction
1Techniques for following reaction rates2 points
- Measuring gas volumeusing a gas syringe or measuring cylinder inverted over a water trough at regular time intervals.
- Measuring change in massplacing the reaction flask on an electronic balance and measuring mass loss as gas escapes (cotton wool plug prevents acid spray while letting gas escape).
2Average rate of reaction formula3 points
- Average rate = Δquantity / Δt
- If measuring volume: units are cm3 s-1 or cm3 min-1.
- If measuring mass: units are g s-1 or g min-1.
- Example: If 36 cm3 of gas is collected between 20 s and 50 s: Average rate = (36 - 15) cm3 / (50 - 20) s = 21 / 30 = 0.70 cm3 s-1.
Section 2 of 2Factors affecting reaction rate & collision theory
1More
2Four factors that alter the rate of reaction4 points
- Decreasing particle size (increasing surface area)Provides a larger exposed surface area of reactant particles, leading to more frequent collisions between reacting particles.
- Increasing concentrationIncreases the number of reactant particles in a given volume, leading to more frequent collisions.
- Increasing temperatureParticles gain kinetic energy and move faster, leading to more frequent collisions.
- More importantly, a much higher proportion of colliding particles possess energy greater than the activation energy.
- Adding a catalystSpeeds up the chemical reaction by lowering activation energy without being chemically changed or consumed at the end of the reaction.
3Graph interpretation3 points
- The reaction is fastest at the very beginning (steepest slope/gradient) because reactant concentrations are at their highest.
- The rate slows down over time as reactants are used up and collisions become less frequent.
- The reaction stops when one of the reactants is completely used up (the graph levels off to a horizontal line).
Last updated:
🌳 Student Search Tree & Frequently Asked Exam Questions: rates of reaction
Step-by-step problem-solving guide, mark scheme criteria, and experimental error analysis curated by Dr. Khaled Dabour (DABOURHUB).
1. Identify all given values and convert non-standard units, 2. State the primary formula or physiological/chemical principle, 3. Calculate to 3 significant figures and clearly state units.
Avoid confusing independent vs dependent variables in practical questions. In calculation questions, double-check percentage change formula: (change / original) × 100.
Where can I find rates of reaction past paper questions by topic with the mark scheme?
On DABOURHUB every rates of reaction question is grouped by syllabus point and shown with the mark-scheme wording, so you can see exactly which sentence earns the mark instead of scrolling through whole year papers.
What is the most common rates of reaction exam question and why do students lose marks on it?
The repeated pattern on IGCSE papers is a short stem that asks you to apply rates of reaction and then justify it with a command word (explain, suggest, compare). Marks are lost by stating the fact without linking it back to the wording of the question, so each rates of reaction item here is written as a full-mark answer.
Is there an alternative to Save My Exams or Physics and Maths Tutor for rates of reaction?
Yes: the rates of reaction notes, topical questions and MCQ quizzes on this site follow the same syllabus headings as the official specification, and they open straight from the search result with no download step.
How do I revise rates of reaction in two weeks before the exam?
Three passes: read the rates of reaction notes once, then do the topical questions and mark them against the mark scheme, then redo only the ones you missed. The quiz on the page gives instant feedback so the third pass takes minutes rather than an evening.