Hydrocarbons Keywords Alkanes – uses, sources and reactions Alkenes – uses, sources and reactions Alkynes – uses, sources and reactions Types 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 bonds Unsaturated– this term is used to describe an organic molecule who has a double or triple bond between their carbons Polyunsaturated – when an organic molecule has many double or triple bonds Melting/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 molecules They can be extracted from crude oil and natural gas Uses Alkanes are primarily used for fuels: Methane Propane Octane 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. Sources Alkenes can be created by cracking alkanes Uses Alkenes can be used for fuel They 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 Combustion Addition – 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 water Oxidation – the use of MnO4- to add two –OH groups In 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. Sources Ethyne is produced when you mix Calcium carbide (CaC2) with water Uses Ethyne (acetylene) is used in welding because it produces a lot of heat when burnt in pure oxygen Reactions Alkynes 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