Download Hydrocarbons

Hydrocarbons
Keywords
Alkanes – uses, sources and
reactions
Alkenes – uses, sources and
reactions
Alkynes – uses, sources and
reactions
Types of reactions - A summary
Author: J R Reid
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
Combustion
Description
Replacing a hydrogen
Substitution
Addition
Adding a hydrogen
Joining unsaturated
molecules together
Adding a halogen
Hydrogenation
Halogenation
Hydrohalogenation
Hydration
Polymerisation
Adding a hydrogen halide
Burning in oxygen
Adding atoms
Adding water