CIE A Level Chemistry
CIE A Level Chemistry Reaction Kinetics Exam Questions
Free CIE A Level Chemistry exam questions for Reaction Kinetics, with a mark scheme for every pack. Covers collision theory, Boltzmann distribution, activation energy, catalysis, rate equations, orders of reaction, rate constants, half-life and reaction mechanisms.
Reaction Kinetics exam questions
1 question pack of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About CIE A Level Chemistry Reaction Kinetics
Reaction kinetics in Cambridge International 9701 explains how fast reactions happen and why. At AS you use collision theory and the Boltzmann distribution to explain the effects of concentration, pressure, temperature and catalysts on rate, and distinguish homogeneous and heterogeneous catalysis. The A Level extension makes this quantitative: rate equations, orders of reaction, rate constants and their units, half-lives, and deducing orders from concentration-time and rate-concentration graphs or initial rates data. You then link the rate equation to the rate-determining step of a mechanism, for example SN1 and SN2. Examiners test Boltzmann sketches, initial-rates tables and the units of k with high frequency.
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.
- Boltzmann distribution A curve of number of molecules against energy starting at the origin and never touching the energy axis. At higher temperature the peak moves right and lower, so a greater proportion of molecules exceed Ea.
- Catalysis A catalyst provides an alternative route with lower activation energy. Homogeneous catalysts are in the same phase as reactants (Fe2+ in the iodide-peroxodisulfate reaction); heterogeneous catalysts are in a different phase (iron in the Haber process) and work by adsorption.
- Rate equations (A Level) Rate = k[A]^m[B]^n, where m and n are orders found by experiment, not from the equation. The overall order is m + n and the units of k depend on it.
- Orders from data and graphs Zero order gives a straight line on a concentration-time graph. First order gives a constant half-life, with k = 0.693/t1/2. On a rate-concentration graph, first order is a straight line through the origin and second order a curve.
- Mechanisms The rate-determining step is the slowest step, and species in the rate equation appear in it or before it. SN1 is first order (rate = k[RX]) and SN2 is second order.
Common mistakes in Reaction Kinetics
- Drawing the Boltzmann curve touching the energy axis or starting above zero; it starts at the origin and approaches but never meets the axis.
- Saying higher temperature increases rate only because of more collisions; the main reason is a greater proportion of collisions with energy above Ea.
- Taking orders from the stoichiometric equation; orders must be found experimentally.
- Getting units of k wrong; rearrange k = rate/concentration terms and cancel mol dm-3 carefully.
- Saying a catalyst is not involved in the reaction; it takes part but is regenerated at the end.
Try three Reaction Kinetics exam-style questions
1. For the reaction A + B → C, rate = k[A]^2[B]. When [A] = 0.20 mol dm-3 and [B] = 0.10 mol dm-3, the rate is 3.0 x 10^-3 mol dm-3 s-1. Calculate k and give its units. (2 marks)
Show the mark scheme answer
k = 3.0 x 10^-3/(0.20^2 x 0.10) = 0.75; units dm6 mol-2 s-1.
2. Use the Boltzmann distribution to explain why increasing temperature increases the rate of reaction. (3 marks)
Show the mark scheme answer
Curve shifts to the right with lower peak; greater proportion of molecules have energy greater than or equal to Ea; more frequent successful collisions (also more frequent collisions).
3. A first order reaction has a half-life of 46 s. Calculate the rate constant. (1 mark)
Show the mark scheme answer
k = 0.693/46 = 0.0151 s-1 (1.51 x 10^-2 s-1).
Reaction Kinetics FAQs
What does Cambridge AS & A Level Chemistry Reaction kinetics cover?
It covers collision theory, the Boltzmann distribution and catalysis at AS, plus rate equations, orders, rate constants, half-life and mechanisms at A Level.
Which parts of Reaction kinetics are tested in Paper 4?
The A Level content, including rate equations, orders from data, half-life, units of k and linking rate equations to mechanisms, is tested in Paper 4.
How do I find orders from an initial rates table?
Pick two experiments where only one concentration changes, compare the factor change in concentration with the factor change in rate, then repeat for the other reactant.
