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Edexcel International A Level Chemistry

Topic 11
Kinetics

Topic 11 turns rate into an equation. It covers the rate equation, orders and the rate constant, the techniques and methods used to collect rate data, deducing orders from concentration–time and rate–concentration graphs and from initial-rate data, the iodine–propanone reaction, the rate-determining step and reaction mechanisms including the evidence for Sₙ1 and Sₙ2, activation energy from the Arrhenius equation, and solid catalysts. It is examined in Unit 4 and assessed practically through Core Practicals 9a, 9b and 10.

Exam Unit
Unit 4
WCH14/01 – IAL
Specification Points
11.1 – 11.13
13 points covered
Topic Parts
8 pages
Revision notes available
Exam Board
Edexcel IAL
Pearson International

Revision Notes

rate = k[A]ᵐ[B]ⁿ
Rate
Equations
orders, k, units of k
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.

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Choose a method
Measuring
Rates
quench, colorimeter, syringe, clock
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.

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Curves and t½
Concentration–
Time Graphs
order from shape, constant half-life
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.

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Compare the runs
Initial-Rates
Method
double [A], what happens to rate?
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.

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Worked example
Iodine and
Propanone
zero order in I₂, rate = k[propanone][H⁺]
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.

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The slow step
Rate-Determining
Step
mechanisms, intermediates, Sₙ1 and Sₙ2
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.

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k = Ae^(−Eₐ/RT)
Arrhenius
Equation
ln k against 1/T, gradient = −Eₐ/R
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.

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Surfaces and cycles
Catalysis
adsorb, weaken, react, desorb
8
Available

Heterogeneous and Homogeneous Catalysis

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

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Specification Coverage

Topic 11 Kinetics – Edexcel International A Level Chemistry

The following specification points outline the knowledge and skills students are expected to demonstrate for Topic 11. Wording follows the Pearson Edexcel International A Level Chemistry specification.

11.1 – 11.5 Rate equations, orders and rate data

11.1
understand the terms:
i
rate of reaction
ii
rate equation, rate=k[A]ᵐ[B]ⁿ where m and n are 0, 1 or 2
iii
order with respect to a substance in a rate equation
iv
overall order of a reaction
ix
heterogeneous and homogeneous catalyst
11.2
a
be able to calculate the half-life of a reaction using data from a suitable graph
b
be able to identify a reaction with a constant half-life as being first order
11.3
be able to select and justify a suitable experimental technique to obtain rate data for a given reaction, including:
i
titration
ii
colorimetry
iii
mass change
iv
volume of gas evolved
11.4
understand experiments that can be used to investigate reaction rates by:
i
an initial-rate method, carrying out separate experiments where different initial concentrations of one reagent are used A ‘clock reaction’ is an acceptable approximation of this method.
ii
a continuous monitoring method to generate data to enable concentration-time or volume-time graphs to be plotted
11.5
be able to deduce the order (0, 1 or 2) with respect to a substance in a rate equation, using data from:
i
a concentration-time graph
ii
a rate-concentration graph
iii
an initial-rate method

11.6 – 11.9 The iodine–propanone reaction, rate-determining step and mechanisms

11.6
understand how to:
i
obtain data to calculate the order with respect to the reactants (and the hydrogen ion) in the acid-catalysed iodination of propanone
ii
use these data to make predictions about species involved in the rate-determining step
iii
deduce a possible mechanism for the reaction
11.7
a
be able to deduce the rate-determining step from a rate equation
b
be able to deduce a rate equation from the rate-determining step
11.8
a
be able to deduce a reaction mechanism using knowledge of the rate equation
b
be able to deduce a reaction mechanism using the stoichiometric equation for a reaction
11.9
a
understand that rate equations for hydrolysis of halogenoalkanes can provide evidence for SN₁ mechanisms in tertiary halogenoalkane hydrolysis
b
understand that rate equations for hydrolysis of halogenoalkanes can provide evidence for SN₂ mechanisms in primary halogenoalkane hydrolysis

11.10 – 11.13 Activation energy, catalysts and core practicals

11.10
a
be able to use calculations to find activation energy from experimental data
b
be able to use graphical methods to find activation energy from experimental data
c
know that the Arrhenius equation will be given if needed
11.11
understand the use of a solid (heterogeneous) catalyst for industrial reactions, in the gas phase, in terms of providing a surface for the reaction
11.12
a
CORE PRACTICAL 9a Following the rate of the iodine-propanone reaction by a titrimetric method
b
CORE PRACTICAL 9b Investigating a clock reaction (Harcourt-Esson, iodine clock)
11.13
CORE PRACTICAL 10 Finding the activation energy of a reaction.