3bPhysical Chemistry

Rates of reaction — Edexcel Modular - OL (Chemistry) Revision Notes & Topical Questions

5 min read 7 parts Lesson 2 of 3 1 quiz

📚 Edexcel Modular - OL (Chemistry) Hub / Topical Revision

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Lesson summary

Rates of reaction Edexcel O Level Modular Chemistry notes: describe experiments to investigate the effects of changes in surface area of a solid, concentration of a solution, temperature and the use of a catalyst on the rate of a reactionTemperature mainly increases rate by incre…

Rates of reaction Edexcel O Level Modular Chemistry: what to do next
Rate of reaction
Collision theory
Activation energy
Boltzmann distribution
Homogeneous catalyst

Section 1 of 7Process & sequence

Particles collide
E ≥ Ea?
Correct orientation?
Successful reaction

Measure gas volume or mass loss at intervals.

Plot against time.

Draw a tangent at the chosen time.

Rate = gradient of the tangent.

Section 2 of 7Keep going

Rates of reaction Edexcel O Level Modular Chemistry: what to do next

These Rates of reaction Edexcel O Level Modular Chemistry notes covered the key ideas, worked examples and exam technique for this topic. Check your Rates of reaction Edexcel O Level Modular Chemistry understanding with the practice questions below, then reread any Rates of reaction Edexcel O Level Modular Chemistry point you were unsure about before moving on.

Practice: Rates of reaction Edexcel O Level Modular Chemistry practice questions

Previous lesson: 3a Energetics — Notes

Next lesson: 3c Reversible reactions and equilibria — Notes

Course: Edexcel Modular – OL (chemistry) — all units

Official syllabus: Pearson Edexcel International GCSEs

Section 3 of 7Compare

Factors affecting rate
Factor	Change	Effect on rate	Explanation	Boltzmann effect	Example
Concentration	Increase	Faster	More frequent collisions	No change in shape	More acid → faster fizz
Pressure (gases)	Increase	Faster	More particles per volume	No change	Haber process
Temperature	Increase 10 °C	Roughly doubles	More particles have E ≥ Ea, more collisions	Curve flattens, shifts right	Food cooks faster
Surface area	Powder	Faster	More exposed particles	—	Powdered CaCO₃
Catalyst	Add	Faster	Lower Ea	More particles above new Ea	Fe in Haber
Light	Increase (some reactions)	Faster	Energy breaks bonds	—	Photochemical chlorination

Section 4 of 7Key terms

Section 5 of 7Syllabus checklist

describe experiments to investigate the effects of changes in surface area of a solid, concentration of a solution, temperature and the use of a catalyst on the rate of a reaction

describe the effects of changes in surface area of a solid, concentration of a solution, pressure of a gas, temperature and the use of a catalyst on the rate of a reaction

explain the effects of changes in surface area of a solid, concentration of a solution, pressure of a gas and temperature on the rate of a reaction in terms of particle collision theory

know that a catalyst is a substance that increases the rate of a reaction, but is chemically unchanged at the end of the reaction

know that a catalyst works by providing an alternative pathway with lower activation energy practical: investigate the effect of changing the surface area of marble chips and of changing the concentration of hydrochloric acid on the rate of reaction between marble chips and dilute hydrochloric acid

practical: investigate the effect of different solids on the catalytic decomposition of hydrogen peroxide solution

Section 6 of 7Command terms

Command terms

Give / State / Name

Recall a fact; one idea per mark.

Define

Give the exact meaning using the specification keywords.

Describe

Give an account of what happens / the pattern in data, quoting values; no reasons needed.

Explain

Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.

Suggest

Use knowledge in a new context; more than one answer may be accepted.

Compare

Similarities and differences; each point must refer to both items.

Calculate

Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.

Discuss

Explore the issue from different angles and link the points.

Evaluate / Assess

Weigh strengths and weaknesses and reach a supported judgement.

Deduce

Draw a conclusion from the information given.

Justify

Support a statement/choice with evidence.

Section 7 of 7Exam technique

Keywords the mark scheme looks for in this lesson

Rate of reaction · Collision theory · Activation energy · Boltzmann distribution · Catalyst · Homogeneous catalyst · Heterogeneous catalyst · Enzyme

Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.

How to get full marks (examiner guidance)

Use specification keywords exactly (e.g. electronegativity, nucleophile, dynamic equilibrium, activation energy).

Link ideas

Link ideas for “explain” each marking point is usually a cause → consequence step; unlinked facts often score nothing.

Use the information in the question

“discuss/evaluate” answers must use the data provided and match the number of marks.

Convert units carefully (mg → g, cm³ → dm³) and show working for calculations.

Avoid vague words

“it”, “stuff”, “things”, “goes up”, “energy is made”. Name the substance and the process.

Do not extrapolate a graph line beyond the data or to zero unless asked.

Six-mark extended responses are marked on content AND a logical, linked line of reasoning.

Last updated: 14 October 2026