0 0 Moodle
Home Revision Notes Courses For Schools Blog My Account Cart
Moodle
Cambridge International AS & A Level Chemistry – Physical Chemistry (A Level)

Topic 26
Reaction Kinetics

Topic 26 covers rate equations, order, overall order, the rate constant, half-life, the rate-determining step and intermediates; deducing orders from concentration–time graphs, initial rates and the half-life method; interpreting graphs and calculating initial rates; the constant half-life of a first-order reaction and k = 0.693 / t½; k from initial rates; mechanisms and the rate-determining step; the qualitative effect of temperature on k; and homogeneous and heterogeneous catalysis with the Haber, catalytic converter, oxides of nitrogen and Fe²⁺/Fe³⁺ examples.

Exam Paper
Paper 4
9701 A Level
Learning Outcomes
26.1 – 26.2
2 sections covered
Topic Parts
8 pages
Revision notes available
Exam Board
Cambridge
9701 (2025 onwards)

Revision Notes

Work through Topic 26 Reaction Kinetics in a structured sequence.

rate = k[A]ᵐ[B]ⁿ
Rate
Equations
1
Available

Rate Equations, Orders and the Rate Constant

Rate equations: orders of reaction, the rate constant k, overall order and working out the units of k.

Start revising
Choose a method
Measuring
Rates
2
Available

Techniques for Measuring Rates

Measuring rates: titration, colorimetry, mass and gas-volume methods, continuous monitoring and the initial-rates method with clock reactions.

Start revising
Curves and t½
Concentration–
Time Graphs
3
Available

Concentration–Time Graphs and Half-Life

Concentration–time graphs: deducing order from the shape, tangents and rates, half-life and first-order reactions, k from the half-life.

Start revising
Compare the runs
Initial-Rates
Method
4
Available

Rate–Concentration Graphs and the Initial-Rates Method

The initial-rates method: rate–concentration graphs, deducing orders from tables of data, writing the rate equation and calculating k.

Start revising
Worked example
Iodine and
Propanone
5
Available

The Iodine–Propanone Reaction

The iodine–propanone reaction: collecting rate data, the orders with respect to iodine, propanone and H⁺, and deducing the mechanism.

Start revising
The slow step
Rate-Determining
Step
6
Available

Rate-Determining Step and Reaction Mechanisms

The rate-determining step: rate equations from mechanisms, mechanisms from rate equations, intermediates, and Sₙ1/Sₙ2 evidence from halogenoalkanes hydrolysis.

Start revising
k = Ae^(−Eₐ/RT)
Arrhenius
Equation
7
Available

Activation Energy and the Arrhenius Equation

The Arrhenius equation: temperature and the rate constant, ln k against 1/T graphs and finding the activation energy from the gradient.

Start revising
Surfaces and cycles
Catalysis
8
Available

Heterogeneous and Homogeneous Catalysis

Catalysis: heterogeneous catalysts at surfaces (adsorption, desorption, the Haber process, catalytic converters) and homogeneous catalysts that are regenerated.

Start revising
Specification Coverage

Topic 26 Reaction Kinetics – Cambridge International A 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.

26.1 Simple rate equations, orders of reaction and rate constants

26.1.1
a
explain and use the term rate equation
b
explain and use the term order of reaction
c
explain and use the term overall order of reaction
d
explain and use the term rate constant
e
explain and use the term half-life
f
explain and use the term rate-determining step
g
explain and use the term intermediate
26.1.2
(a)
understand and use rate equations of the form rate = k[A]ᵐ[B]ⁿ (for which m and n are 0, 1 or 2)
(b)-i
deduce the order of a reaction from concentration–time graphs
(b)-ii
deduce the order of a reaction from experimental data relating to the initial rates method
(b)-iii
deduce the order of a reaction from experimental data relating to the half-life method
(c)-i
interpret experimental data in graphical form, including concentration–time graphs
(c)-ii
interpret experimental data in graphical form, including rate–concentration graphs
(d)
calculate an initial rate using concentration data
(e)
construct a rate equation
26.1.3
(a)
show understanding that the half-life of a first-order reaction is independent of concentration
(b)
use the half-life of a first-order reaction in calculations
26.1.4
(a)
calculate the numerical value of a rate constant, for example by using the initial rates and the rate equation
(b)
calculate the numerical value of a rate constant, for example by using the half-life, t½, and the equation k = 0.693/t½
26.1.5
for a multi-step reaction:
(a)
suggest a reaction mechanism that is consistent with the rate equation and the equation for the overall reaction
(b)
predict the order that would result from a given reaction mechanism and rate-determining step
(c)
deduce a rate equation using a given reaction mechanism and rate-determining step for a given reaction
(d)
identify an intermediate or catalyst from a given reaction mechanism
(e)
identify the rate determining step from a rate equation and a given reaction mechanism
26.1.6
describe qualitatively the effect of temperature change on the rate constant and hence the rate of a reaction

26.2 Homogeneous and heterogeneous catalysts

26.2.1
explain that catalysts can be homogeneous or heterogeneous
26.2.2
a
describe the mode of action of a heterogeneous catalyst to include adsorption of reactants
b
describe the mode of action of a heterogeneous catalyst to include bond weakening
c
describe the mode of action of a heterogeneous catalyst to include desorption of products
(a)
describe the mode of action of a heterogeneous catalyst, for example iron in the Haber process
(b)
describe the mode of action of a heterogeneous catalyst, for example palladium, platinum and rhodium in the catalytic removal of oxides of nitrogen from the exhaust gases of car engines
26.2.3
describe the mode of action of a homogeneous catalyst by being used in one step and reformed in a later step
(a)
describe the mode of action of a homogeneous catalyst, for example atmospheric oxides of nitrogen in the oxidation of atmospheric sulfur dioxide
(b)
describe the mode of action of a homogeneous catalyst, for example Fe₂+ or Fe₃+ in the I⁻/S₂O82– reaction