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Hydrocarbons

Hydrocarbons. Keywords Alkanes – uses, sources and reactions Alkenes – uses, sources and reactions Alkynes – uses, sources and reactions Types of reactions - A summary. Keywords.

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Hydrocarbons

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  1. Hydrocarbons Keywords Alkanes – uses, sources and reactions Alkenes – uses, sources and reactions Alkynes – uses, sources and reactions Types of reactions - A summary

  2. 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)

  3. 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)

  4. 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

  5. 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

  6. 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)

  7. 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

  8. Types of Reactions – a summary • Match the terms with the summaries below:

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