CCEA A Level Chemistry
CCEA A Level Chemistry 2.9 Kinetics Exam Questions
Free CCEA A Level Chemistry revision for 2.9 Kinetics: what you need to know, common mistakes and exam-style questions with answers. Covers factors affecting rate, collision theory, activation energy, Maxwell-Boltzmann distributions and the effect of temperature and catalysts.
Practise 2.9 Kinetics with past papers
Once you have learnt this topic, find the 2.9 Kinetics questions in real CCEA A Level Chemistry past papers and mark them with the mark scheme. Doing lots of real questions is the quickest way to learn how examiners ask about each idea.
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About CCEA A Level Chemistry 2.9 Kinetics
Section 2.9 of Unit AS 2 is the qualitative introduction to reaction rates. You need to explain how concentration, pressure, temperature and catalysts affect the rate of a reaction using collision theory and activation energy. A large part of the section is the Maxwell-Boltzmann distribution: you must sketch curves at two temperatures and show how a catalyst changes the number of molecules with enough energy to react. Explanations must refer to the frequency of successful collisions and the proportion of molecules with energy greater than or equal to the activation energy. Quantitative rate equations follow in A2 1 (4.3 Rates of Reaction).
What you need to know
- Collision theory Particles must collide with energy at least equal to the activation energy and with the correct orientation. Rate depends on the frequency of successful collisions.
- Concentration and pressure Higher concentration or pressure means more particles per unit volume, so more frequent collisions and more successful collisions per second.
- Temperature At higher temperature, particles have more kinetic energy and collide more often, but the main effect is that a much larger proportion have energy greater than or equal to the activation energy.
- Maxwell-Boltzmann distribution A curve of number of molecules against energy, starting at the origin, with no maximum energy (it approaches but never meets the x-axis). At a higher temperature the peak moves right and is lower, with more molecules beyond Ea. The area under the curve is unchanged.
- Catalysts A catalyst provides an alternative route with a lower activation energy, so more molecules have enough energy to react. It is not used up. On the distribution, Ea is marked further left, not the curve moved.
Common mistakes in 2.9 Kinetics
- Saying the curve moves when a catalyst is added. The curve stays the same; only the position of Ea moves to the left.
- Drawing the Maxwell-Boltzmann curve touching the x-axis at high energy. It approaches the axis but never touches it.
- Saying higher temperature increases rate only because collisions are more frequent. The key reason is more molecules have energy at least equal to Ea.
- Saying a catalyst increases the energy of particles. It lowers the activation energy by providing an alternative route.
- Drawing the high temperature curve with a higher peak. It is lower and broader with the same total area.
Try three 2.9 Kinetics exam-style questions
1. Explain, using the Maxwell-Boltzmann distribution, why a small rise in temperature greatly increases the rate. (3 marks)
Show the mark scheme answer
At higher temperature the distribution shifts to the right; many more molecules have energy greater than or equal to Ea; frequency of successful collisions increases greatly.
2. Explain how a catalyst increases the rate of a reaction. (2 marks)
Show the mark scheme answer
Provides an alternative reaction pathway with lower activation energy; a greater proportion of collisions are successful.
3. State why increasing pressure increases the rate of a gaseous reaction. (2 marks)
Show the mark scheme answer
More molecules per unit volume; more frequent collisions (so more successful collisions per unit time).
2.9 Kinetics FAQs
What does CCEA A Level Chemistry 2.9 Kinetics cover?
It covers factors affecting rate, collision theory, activation energy and Maxwell-Boltzmann distributions for temperature changes and catalysts.
Which unit is 2.9 Kinetics examined in?
It is examined in Unit AS 2: Further Physical and Inorganic Chemistry and an Introduction to Organic Chemistry, a 1 hour 30 minute paper with a multiple-choice section and structured questions. Related practical skills can also be assessed in Unit AS 3.
How do I draw a Maxwell-Boltzmann curve properly?
Start at the origin, show a single peak skewed to the left, and a tail that never touches the energy axis. Label the axes and mark Ea, and keep areas equal when comparing two temperatures.
