12 - Alkanes complete saga

Crude oil is a mixture of different ?

hydrocarbons

hydrocarbon separated into the separate molecules by ?

fractional distillation

Crude oil can be separated into the separate molecules by fractional distillation as the different chain lengths of molecules result in them having

different boiling points.

Fill da blank ; Crude oil is separated in the following way:

1. The mixture is vapourised and fed into the [A] column.

2. [b] rises, cool and condense.

3. Products are siphoned off for [c] uses.

A= B= C=

A= fractionating
B= Vapours
C= different

Products with short carbon chains have lower ?

boiling points

Products with long carbon chains have ?

higher boiling points

The compounds collected from the fractionating column are then broken down further via the method of ?

cracking

Longer carbon chains are not very useful, therefore they are broken down to form ?

smaller, more useful molecules.

Why are harsh conditions used in cracking ?

Carbon Double bond

Thermal Cracking produces a high proportion of ?

alkanes and alkenes

Thermal cracking conditions

High temperatures around 1200 K and pressures around 7000 kPa are used to crack the carbon chains.

Catalytic Cracking produces aromatic compounds with ?

carbon rings

Catalytic cracking conditions ?

Lower temperatures around 720 K are used along with normal pressure, but a zeolite catalyst is needed to compensate for these less harsh conditions.

Alkanes make good fuels as they release a lot of energy when ?

burned

With sufficient oxygen present, they undergo what ?

complete combustion

complete combustion of alkane products?

produces carbon dioxide and water.

methane combustion

CH4 + 2O2 -> CO2 + 2H2O

If the oxygen present is insufficient, combustion is incomplete and what is produced ?

carbon monoxide is produced alongside water

Carbon monoxide is a toxic gaseous product which is especially dangerous to humans as it has no

odor or colour

catalytic converter uses which catalyst ?

a rhodium one

Alkanes react with halogens in the presence of what to produce halogenoalkanes ?

UV light

Alkanes react with halogens in the presence of UV light to produce halogenoalkanes .Why is UV light needed ?

breaks down the halogen bonds producing reactive intermediates called free radicals

Initiation is when ?

the halogen is broken down

Propagation is when

a hydrogen is replaced and the Cl• radical reformed as a catalyst

Termination is when

two radicals join to end the chain reaction and form a stable product

Cl2 initiation step ?

Cl2 -> 2cl.

Free radical shown using ?

A dot