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Cambridge International AS & A Level Chemistry – Physical Chemistry

Topic 8
Reaction Kinetics

Topic 8 covers rate of reaction and effective collisions, the effect of concentration and pressure, calculating rate from experimental data, activation energy and the Boltzmann distribution, the effect of temperature, and catalysis: the lower-energy mechanism, its effect on the Boltzmann distribution, and reaction pathway diagrams with and without a catalyst. Rate equations and orders follow in Topic 26.

Exam Papers
Papers 1 & 2
9701 AS Level
Learning Outcomes
8.1 – 8.3
3 sections covered
Topic Parts
4 pages
Revision notes available
Exam Board
Cambridge
9701 (2025 onwards)

Revision Notes

Work through Topic 8 Reaction Kinetics in a structured sequence.

Collision theory
Rates of
Reaction
1
Available

Collision Theory and Rates of Reaction

Collision theory: rate of reaction, activation energy, effective collisions and the effects of concentration, pressure, surface area and temperature.

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Gradients
Measuring
Rates
2
Available

Measuring and Calculating Rates

Measuring rates: mass, gas volume and clock methods, rate = 1/time, tangents and initial rate on concentration–time graphs.

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Energy spread
Boltzmann
Distribution
3
Available

The Maxwell–Boltzmann Distribution

The Boltzmann distribution: shape, activation energy, the effect of temperature and the effect of a catalyst on the proportion of molecules that can react.

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Lower Eₐ
Catalysts
4
Available

Catalysts and Reaction Profiles

Catalysts: lower activation energy, reaction pathway diagrams with the intermediate, homogeneous and heterogeneous catalysis, and the economic and environmental benefits.

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Specification Coverage

Topic 8 Reaction Kinetics – Cambridge International AS Level Chemistry

The following Cambridge learning outcomes state what candidates should be able to do. Wording is taken from the Cambridge International AS & A Level Chemistry (9701) syllabus.

8.1 Rate of reaction

8.1.1
explain and use the terms rate of reaction, frequency of collisions, effective and non-effective collisions
8.1.2
explain qualitatively, in terms of frequency of effective collisions, the effect of concentration and pressure changes on the rate of a reaction
8.1.3
use experimental data to calculate the rate of a reaction

8.2 Effect of temperature on reaction rates and the concept of activation energy

8.2.1
define activation energy, Eₐ, as the minimum energy required for a collision to be effective
8.2.2
sketch the Boltzmann distribution and use it to explain the significance of activation energy
8.2.3
explain qualitatively, in terms both of the Boltzmann distribution and of frequency of effective collisions, the effect of temperature change on the rate of a reaction

8.3 Homogeneous and heterogeneous catalysts

8.3.1
explain and use the terms catalyst and catalysis, and explain that:
a
in the presence of a catalyst, a reaction has a different mechanism, i.e. one of lower activation energy
b
this catalytic effect can be explained in terms of the Boltzmann distribution
c
a reaction pathway diagram can be constructed and interpreted for a reaction in the presence and absence of an effective catalyst