3.3.2 - Alkanes

Question 1

Crude oil

Answer 1

A mixture of different hydrocarbons that can be separated into separate molecules by fractional distillation as different chain lengths of molecules result in them having different boiling points

Question 2

Crude oil is separated in the following way…

Answer 2

The mixture is vapourised and fed into the fractioning column. Vapours rise, cool and condense. Products are siphoned off for different uses

Question 3

Short carbon chains are at the…

Answer 3

top of the column

Question 4

Products with long carbon chains are at the…

Answer 4

Bottom of the column

Question 5

Thermal cracking

Answer 5

Produces a high proportion of alkanes and alkenes. High temperatures around 1200K and 7000 kPa are used to crack the carbon chains

Question 6

Catalytic cracking

Answer 6

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

Question 7

Equation for complete combustion of alkanes

Answer 7

CH4 + 2O2 —> CO2 + 2H2O

Question 8

Equation for incomplete combustion of alkanes

Answer 8

2CH4 + 3O2 —> 2CO + 4H2O

Question 9

Catalytic converter

Answer 9

Uses a rhodium catalyst to convert harmful products into more stable products such as CO2 or H2O

Question 10

Carbon particulates

Answer 10

Produced by incomplete combustion. Small fragments of unturned hydrocarbon. Unless removed from waste products, can cause serious respiratory problems as they pollute air

Question 11

Initiation

Answer 11

The halogen is broken down
Cl2 —> 2Cl.

Question 12

Propagation

Answer 12

A hydrogen is replaced and the Cl. radical reformed as a catalyst
Cl. + CH4 —> .CH3 + HCl
.CH3 + Cl2 —> CH3Cl + Cl.

Question 13

termination

Answer 13

Two radicals join to end the chain reaction and form a stable product
.CH3 + .CH3 —> C2H6