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Topic 6B Alkanes, taught by a specialist chemistry teacher.

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Lesson 4 of 4

Substitution Reactions of Alkanes

This virtual lesson focuses on the substitution reactions of alkanes, introducing the key mechanism by which alkanes undergo chemical reactions.

The lesson opens by introducing the free radical substitution mechanism, explaining how relatively unreactive alkanes can react in the presence of UV light.

The mechanism is broken down into three key stages: initiation, where free radicals are formed by homolytic fission; propagation, where radicals react to form products while regenerating new radicals; and termination, where radicals combine to form stable molecules, ending the chain reaction.

Further substitution is also examined, where multiple hydrogen atoms in an alkane can be replaced, leading to a mixture of products. This highlights the challenges in controlling reactions involving free radicals.

This lesson develops understanding of reaction mechanisms, radical chemistry, and the behaviour of alkanes under reactive conditions.

Specification points for Topic 6B

6.10understand that alkane fuels are obtained from the fractional distillation, cracking and reforming of crude oil
6.11know that pollutants, including carbon monoxide, oxides of nitrogen and sulfur, carbon particulates and unburned hydrocarbons, are formed during the combustion of alkane fuels
6.12understand the problems arising from pollutants from the combustion of fuels, limited to the toxicity of carbon monoxide and the acidity of oxides of nitrogen and sulfur
6.13understand how the use of a catalytic converter solves some problems caused by pollutants
6.14understand the use of alternative fuels, including biodiesel and alcohols derived from renewable sources such as plants, in terms of a comparison with non-renewable fossil fuels
6.15know that a radical:i
6.16understand the reactions of alkanes with:i
6.17understand the limitations of the use of radical substitution reactions in the synthesis of organic molecules, in terms of further substitution reactions and the formation of a mixture of products
6.23understand that heterolytic bond fission of a covalent bond results in the formation of ions

Substitution Reactions of Alkanes

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