The Alkenes Flashcards
What is an alkene?
An unsaturated hydrocarbon, with the general formula: CnH2n
What happens to the boiling points of alkanes as the Mr increases?
As the Mr increases, the number of electrons increases, so the van der waals force increases, so the boiling point increases.
What is the trend with the solubility of alkenes and why?
Alkenes are virtually insoluble in water as they can’t Hydrogen bond with water
What are the conditions with alkenes for geometric isomers to occur?
Both atoms must have 2 different groups of either side of the C=C double bond
What are the conditions for Cis/ Trans notation to be used?
When both atoms of C=C have a hydrogen and one other group attached.
For E/Z isomers what isomer is it when the highest atomic numbers are opposite?
E (or trans)
What do alkenes produce when the combust (/burn) in air?
Carbon dioxide and water
Why do we not use alkenes for fuel?
As they are much more valuable for other purposes like making plastics
Why are alkenes more reactive than alkanes?
As they are unsaturated (C=C double bond) and can undergo addition reactions
What is a double bond and why does it attract electrophiles?
It is a region of high electron denisity so attracts electrophiles (electron pair acceptors)
What is an electrophile?
A electron pair acceptor
What are the typical reactions of alkenes called?
Electrophilic Addition Reactions
What are the conditions needed for ethene to react with hydrogen to produce ethane and what is this reaction used for?
Conditions: Finely divided Nickel catalyst at about 150 degrees Celsius
Used to make margarine.
What is used as the test for a alkene/ C=C double bond?
Reaction with bromine water (if it has a C=C double bond, bromine goes orange to colour
Why are alkyl hydrogensulfates useful?
They can easily be converted into alcohols by reaction with water (hydrolysis)
What is produced when concentrated sulphuric acid is added across a double bond?
Alkyl Hydrogensulfates
What is produced when Hydrogen halides are used to add across the C=C bond of an alkene?
They produce a haloalkane
When can we get more than more possible product in an addition reaction?
When an unsymmetrical molecule is being added to an unsymmetrical alkene
What is the trend is the stability of carbocation intermediates?
Most Stable Tertiary
Secondary
Least Stable Primary
What is the definition of polymerisation?
A process in which lots of small molecules called monomers join together to form a large molecule (polymer) which consists of repeating molecules
What are addition polymers?
Long chain molecules formed when lots of small molecules (monomers) join together to form one big molecule (a polymer) with nothing else formed
What determines the properties of a polymer?
They are determined by its chemical structure and intermolecular forces
What are the properties of poly(ethene) and what is an example of something made out of poly(ethene)?
It is strong and flexible
e.g bags
What are the properties of PVC and what is an example of something made out of PVC?
Strong and Hard
e.g Window Frames
How can we modify the properties of a polymer?
By adding substances called plasticisers
How does adding a plasticiser change the properties and why?
It makes the polymer more flexible as the plasticiser molecules push the chains apart, so there is weaker Intermolecular forces.
What are the properties of PVC and plasticiser and what is an example of something made out of PVC and plasticiser?
Strong and flexible
e.g wellies
Why are addition polymers non-biodegradable?
As they are unreactive
What 3 methods do we have to dispose of polymers
- Landfill (but the bacteria is not evolved to dispose of it)
- Incineration
- Recycling
