Who this is for: Cambridge IGCSE Coordinated Science (0654) students who want rate of reaction — collision theory, factors that change speed and how to measure rates — to become a reliable source of marks instead of a list-memorising exercise.
What query it owns: how to understand and revise rate of reaction in Cambridge IGCSE Coordinated Science.
Why this is safe: this page owns the rate-of-reaction revision-guide angle, while Tutopiya’s Rate (Speed) Of Reaction subtopic page owns the learning resource and the free Rate (Speed) Of Reaction quiz owns the practice.

The rate of a reaction is how quickly reactants are used up or products form. Cambridge IGCSE Coordinated Science (0654) expects you to explain rates using collision theory, describe how temperature, concentration, surface area, pressure and catalysts affect speed, and interpret rate graphs. This guide links each factor to particle-level reasoning examiners reward.

Key takeaways

• Reactions occur when particles collide with sufficient energy (≥ activation energy) and correct orientation.
• Higher temperature → faster particles → more frequent energetic collisions → faster rate.
• Higher concentration or pressure (gases) → more particles per unit volume → more collisions.
• Greater surface area → more exposed particles → more collisions.
• Catalysts lower activation energy without being used up; increase rate.

What is rate of reaction in Cambridge IGCSE Coordinated Science?

Rate measures how quickly a reaction proceeds. Collision theory states that reactant particles must collide with enough energy to overcome the activation energy barrier. Anything that increases the frequency of successful collisions — or lowers the energy barrier — increases the rate.

You can read the full explanation, practical methods and notes on Tutopiya’s Rate (Speed) Of Reaction subtopic page before you attempt questions.

Factors affecting rate — summary table

Factor	Effect on particles	Effect on rate
Temperature ↑	Faster movement; more collisions exceed Eₐ	Increases
Concentration ↑	More particles per dm³; more collisions	Increases
Pressure ↑ (gas)	Particles closer; more collisions	Increases
Surface area ↑	More particles exposed at surface	Increases
Catalyst added	Lowers activation energy	Increases

Measuring rate — common methods

Method	What is measured	Example reaction
Gas volume / mass loss	Volume of gas or mass decrease over time	Mg + acid → H₂
Colour change / turbidity	Disappearance of colour or formation of precipitate	Na₂S₂O₃ + HCl
pH change	Change in acidity over time	Ester hydrolysis

Rate of reaction in past-paper wording

Command word	What the question wants	Typical stem
Explain	Particle-level reason for rate change	”Explain why powdered zinc reacts faster than a strip.”
Describe	How to measure rate	”Describe how you would measure the rate of CO₂ production.”
Sketch / interpret	Rate graph features	”Sketch a graph of volume of gas against time.”
State	Factor or definition	”State two factors that increase reaction rate.”

Worked exam-style stems

1. “Explain why increasing temperature increases the rate of reaction.” Particles gain kinetic energy, move faster, collide more frequently, and a greater proportion of collisions have energy ≥ activation energy. Reward: faster particles + more collisions + more energetic collisions.
2. “Explain why a catalyst increases rate without being used up.” A catalyst provides an alternative pathway with lower activation energy, so more collisions are successful; it is regenerated at the end. Reward: lower Eₐ + not consumed.
3. “Describe how you would measure the rate of hydrogen production from magnesium and acid.” Collect gas in a gas syringe / measure mass loss on a balance; record volume or mass at regular time intervals; plot graph. Reward: valid method + time intervals + measurable quantity.

Test yourself with the Rate (Speed) Of Reaction quiz once you can explain each factor using collision theory.

How rate of reaction connects to the syllabus

Rate links to energy changes (activation energy), particle theory and practical skills. It precedes reversible reactions and equilibrium in later study. The Cambridge IGCSE Coordinated Science resource hub links every Chemical Reactions subtopic.

Common mistakes students make

• Saying particles collide more without mentioning energetic collisions at higher temperature.
• Confusing concentration with amount of substance (same amount, different volume changes concentration).
• Stating catalysts are used up in the reaction.
• Drawing rate graphs that rise continuously (gas volume curves level off as reactant is used up).
• Explaining surface area without linking to more exposed particles.

When you need more support

If collision theory explain questions keep costing marks, work through the Rate (Speed) Of Reaction quiz, then get focused help from a Cambridge IGCSE Coordinated Science tutor.

Frequently asked questions

Is rate of reaction hard in Coordinated Science? Collision theory gives a clear framework — link each factor to particle collisions and activation energy.

What is activation energy? The minimum energy colliding particles need for a reaction to occur.

How does a catalyst work? It lowers activation energy by providing an alternative reaction pathway and is not used up.

How do I revise rate of reaction effectively? Learn the five factors with particle explanations, practise graph interpretation, then take the quiz.

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