T7 - Alkenes, Cracking and Addition Polymers Flashcards
what functional group do alkenes belong to?
Alkenes are a homologous series which contain a carbon-carbon double bond
what is the general formula for alkenes
CnH2n
Why are alkenes classified as unsaturated
they contain a carbon-carbon double bond
what happens when bromine water is shaken with an alkane
it would not react and remain as an orange solution because alkanes do not have a carbon-carbon double bond so the bromine remains in a solution
what happens when bromine is shaken with an alkene
the double bond is broken and the bromine atoms are added to the solution causing the colour to change from orange to colourless
what is the reaction between alkenes and bromine called
an addition reaction
What happens when alkanes react with halogens in the presence of UV light
alkanes do react with bromine in the presence of UV light. When this happens - a hydrogen atom in the alkane is replaced by a bromine atom
what type of reaction takes place when one atom is replaced by another
a substitution reaction
what type of reaction takes place when an atom or group of atoms is added to a molecule without taking anything away
an addition reaction
what reaction takes place when there is a reaction with oxygen ‘aka’ burning
a combustion reaction
what is a long-chain hydrocarbon
hydrocarbons with a large number of hydrocarbon molecules
what is a short-chain hydrocarbon
hydrocarbons with a small number of hydrocarbon molecules
how can you convert alkenes to alkanes
catalytic cracking
how does catalytic cracking work
- hydrocarbons are heated to vapourise at 600-700 degrees celcius
- these vapours will then pass over a hot catalyst of silica or alumina which breaks down covalent bonds in molecules causing thermal decomposition to occur
- this produces smaller alkenes and alkanes
what can be used as catalysts in catalytic cracking
silica or alumina
what is thermal decomposition
the breaking down of a substance by heating
what type of reaction is cracking
an endothermic reaction
why is cracking necessary for supply vs demand
in fractions where there is a surplus and a lower demand such as fuel oil and bitumen, they can be cracked and modified into fractions where there is a higher demand and a lower supply such as petrol, kerosene and diesel
How is an addition polymer formed?
joining up many small molecules called monomers
polymers are inert. What does this mean
they are unreactive
why are polymers inert
they have strong C-C bonds
why are polymers unable to biodegrade
they have strong C-C bonds
what happens when addition polymers are burned
large amounts of heat energy and carbon dioxide are released into the atmosphere - contributing to climate change
