Chemistry - Alkenes and addition polymers

What do alkenes contain?

A carbon-carbon double bond

What is the general formula for alkenes?

CnH2n

What does unsaturated mean?

Contains double bonds

What is a homologous series?

A family of organic compounds that react in the same way, and have the same general formula.

What are hydrocarbons?

Molecules containing hydrogen and carbon atoms only.

Why are alkenes unsaturated?

They contain two fewer hydrogen atoms than the alkane with the same number of carbon atoms and they contain a double bond.

What are the first four alkenes?

Ethene, propene, butene, and pentene

How can alkene molecules be represented?

Using molecular and displayed formulae

What determines the reactions of organic compounds?

Their functional group

How do alkenes react with bromine water?

They turn it from orange to colourless

How do alkenes react with oxygen?

They combust in the same way as other hydrocarbons.

How do alkenes react with hydrogen, water and the halogens?

By the addition of atoms across the carbon-carbon double bond so that it becomes a single bond.

What can alkenes be used to make?

Polymers such as poly(ethene) and poly(propene) by addition polymerisation

What happens in addition polymerisation?

Many small molecules (monomers) join together to form very large molecules (polymers).

In addition polymerisation, what is the similarity between the repeating unit and the monomer?

They have the same atoms because no other molecule is formed in the reaction.

How are the atoms in polymer molecules linked?

By strong covalent bonds

Why are polymers solids at room temperature?

The intermolecular forces between polymer molecules are relatively strong

What do the properties of polymers depend on?

The monomers they are made from and the conditions under which they are made

What is the difference between thermosofting polymers and thermosetting polymers?

Thermosoftening polymers melt when they are heated and thermosetting polymers don't.

What are plastics produced from?

Limited, raw materials

Where does much of the energy for the processes of making plastics come from?

Limited resources (crude oil)

Why are alkenes rarely burned/combusted?

They are too valuable for making polymers and they tend to undergo incomplete combustion with smoky flames.

What does incomplete combustion of alkenes produce?

Water, soot (carbon) and carbon monoxide which is odourless, tasteless, colourless, and poisonous.

What is a monomer?

The individual subunit that polymers are made from

What is a polymer?

A long chain of monomers together

What are the problems with polymers?

Come from crude oil which is a finite resource and they are difficult to dispose of due to the many strong covalent bonds.

Why do the weak intermolecular forces in polymers require lots of energy to overcome?

Because there is a lot of them so added together they are stronger.

How many branches are there on low density polymer molecules?

Many

How many branches are there on high density polymer molecules?

Few

What is the relative strength of low density polymer molecules (LDPE)?

Weak

What is the relative strength of high density polymer molecules (HDPE)?

Strong

What is the maximum usable temperature of LDPEs?

85 degrees C

What is the maximum usable temperature of HDPEs?

120 degrees C

How are LDPEs formed?

Under high pressure and about 170 degrees C

How are HDPE's formed?

Under low pressure, at around 70 degrees C and with a catalyst.

What are the properties of thermosoftening polymers?

Tangled polymer chains, no cross-links between chains, weak forces of attraction between chains, and softens when heated.

What are the properties of thermosetting polymers?

Polymer chains held together by strong, covalent, cross-link bonding that does not break on heating, and it remains hard when heated.