Author: J R Reid

Hydrocarbons

KeywordsAlkanes – uses, sources and

reactionsAlkenes – uses, sources and

reactionsAlkynes – uses, sources and

reactionsTypes of reactions - A summary

Keywords

These chemicals that we will be studying in this section are called hydrocarbons (they are composed of hydrogen and carbon). When discussing them we use a number of key words:

Saturated – this term is used to describe an organic molecule who has no double or triple bondsUnsaturated– this term is used to describe an organic molecule who has a double or triple bond between their carbonsPolyunsaturated – when an organic molecule has many double or triple bondsMelting/boiling point – the temperature at which the specific molecule boils or melts. There is an important trend to do with this – as the molecule gets bigger the melting and boiling points get higher (they are harder to melt)

Alkanes – Uses and sources

Alkanes are saturated organic molecules.Sources

They can be made by adding hydrogen to unsaturated organic moleculesThey can be extracted from crude oil and natural gas

UsesAlkanes are primarily used for fuels:

MethanePropaneOctane

They can also be used for lubricants (e.g. machine oil) and road surfaces (bitumen)

Alkanes - Reactions

Combustion – the burning of alkanes in oxygen to produce CO2 and H2O

Cracking – the snapping of long chain alkanes to produce an alkane and an alkene

Substitution – when a hydrogen is swapped with a different element – normally a halogen

Alkenes – Uses and sources

Alkenes have a double bond present somewhere in their structure. This bond can be snapped open and other elements bonded to it. This makes them quite handy.

SourcesAlkenes can be created by cracking alkanes

UsesAlkenes can be used for fuelThey can be used as a building block for alkanes, alcohols and haloalkanes (see next page)They can be used to create various plastics

Alkenes - Reactions

CombustionAddition – when a double bond is broken and other components are added. There are a number of different types of addition reactions:

Hydrogenation – the addition of hydrogen (with a Pt catalyst)Halogenation – the addition of a halogen (e.g. Cl2)Hydrohalogenation – the addition of a hydrogen halide (e.g. HCl)Hydration – the addition of waterOxidation – the use of MnO4

- to add two –OH groupsIn each of these cases what type of chemical would

be produced?Polymerisation – this is the linking together of many alkenes to create long chained organic molecules (plastics like polyethene)

Alkynes

Alkynes have triple bonds and behave in a very similar way to alkenes except that they are more reactive. This means that there is no natural source of alkynes.

SourcesEthyne is produced when you mix Calcium carbide (CaC2) with water

UsesEthyne (acetylene) is used in welding because it produces a lot of heat when burnt in pure oxygen

ReactionsAlkynes have exactly the same type of reactions as alkenes

Types of Reactions – a summary

Match the terms with the summaries below:

Type Description

Combustion Replacing a hydrogen

Substitution Adding a hydrogen

Addition Joining unsaturated molecules together

Hydrogenation Adding a halogen

Halogenation Adding a hydrogen halide

Hydrohalogenation

Burning in oxygen

Hydration Adding atoms

Polymerisation Adding water