Factors Affecting the Rate of Reaction
Get to grips with Factors Affecting the Rate of Reaction for GCSE Chemistry with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Rate increases with higher concentration, higher temperature, larger surface area and the presence of a catalyst.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Four factors affect the rate of a chemical reaction: concentration or pressure, surface area, temperature, and the presence of a catalyst.
Increasing the concentration of a solution, or the pressure of a gas, increases the rate because the particles are closer together, so collisions are more frequent. Increasing the surface area of a solid does the same by exposing more particles to collide with.
Increasing temperature increases the rate for two reasons: particles move faster so collide more frequently, and a greater proportion of collisions have enough energy to be successful. A catalyst provides a different pathway with a lower activation energy.
Revision notes
Concentration, pressure and surface area
Higher concentration or pressure means particles are closer together, so collisions are more frequent.
Greater surface area, achieved by using a powder rather than lumps, exposes more particles so more collisions can occur. Both increase the frequency of collisions.
Temperature
Increasing temperature increases the rate in two ways.
Particles have more kinetic energy so move faster and collide more frequently. A greater proportion of collisions also have energy equal to or greater than the activation energy, so more collisions are successful. Both points are needed for full marks.
Catalysts
A catalyst speeds up a reaction without being used up and without changing the products.
It provides a different reaction pathway with a lower activation energy, so a greater proportion of collisions are successful. Enzymes are biological catalysts.
Key points
- Higher concentration increases the rate.
- Higher pressure increases the rate for gases.
- Greater surface area increases the rate.
- Higher temperature increases collision frequency and energy.
- A catalyst lowers the activation energy.
- A catalyst is not used up in the reaction.
Worked examples
Example 1
Explain why powdered marble reacts faster with acid than marble chips. [2 marks]
Model answer
Powder has a much larger surface area than chips of the same mass (1 mark), so more particles are exposed and collisions between the acid and the marble are more frequent (1 mark).
Example 2
Explain why increasing the temperature increases the rate of reaction. [3 marks]
Model answer
The particles gain more kinetic energy so move faster and collide more frequently (1 mark). A greater proportion of the collisions also have energy equal to or greater than the activation energy (1 mark), so more collisions are successful (1 mark).
Example 3
Explain how a catalyst increases the rate of a reaction. [2 marks]
Model answer
A catalyst provides an alternative reaction pathway with a lower activation energy (1 mark), so a greater proportion of collisions have enough energy to be successful (1 mark).
Common mistakes
Giving only one reason for the temperature effect.
Both increased collision frequency AND increased proportion of successful collisions are needed.
Saying a catalyst is used up.
It is not used up and is chemically unchanged at the end.
Saying more surface area means more particles.
The number of particles is the same; more are exposed at the surface.
Saying a catalyst increases the activation energy.
It lowers it.
Exam tips
- Give both reasons when explaining the temperature effect.
- Say collisions are more frequent, not just more collisions.
- Define a catalyst as not used up and not changing the products.
- Link every factor back to collision frequency or energy.
Key terms
- Rate
- How quickly a reaction proceeds.
- Surface area
- The area of solid exposed to react.
- Catalyst
- A substance speeding up a reaction without being used up.
- Activation energy
- The minimum energy needed for a successful collision.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.