Alkanes 3.3.2

Question 1

What does thermal cracking mean?

Answer 1

Thermal cracking takes place at high pressure and produces a high percentage of alkenes.

Question 2

What does catalytic cracking mean?

Answer 2

takes place at a slight pressure , high temperature and in the presence of a zeolite catalyst and is used mainly to produce motor fuels and aromatic hydrocarbons

Question 3

what’s the general formula for alkanes?

Answer 3

CnH2n+2

Question 4

Why is cracking long chain hydrocarbons into shorter hydrocarbons more useful?

Answer 4

Short chain hydrocarbons are better fuels (e.g. petrol , natural gas ) and are higher in demand.

Question 5

What is the process of fractional distillation and crude oil ?

Answer 5

1) mixture is vaporised and fed into fractionating column.
2) vapours rise , cool and condense
3) products are siphoned off for different uses.

• Products with short carbon chains = lower boiling points so they rise higher up the column before reaching their boiling point. They’re collected at the top of the column
• products with Long carbon chains = higher boiling point so they are low down in the fractionating column. They condense and are collected at the bottom.

Question 6

What pollutants will burning hydrocarbon - based fuels produce?

Answer 6

• carbon monoxide
• sulfur dioxide
• Nitrogen oxides

Question 7

What are flue gases?

Answer 7

Gases released from factory processes / power stations

Question 8

How can you remove SO2 from flue gases?

Answer 8

Use calcium oxide or calcium carbonate

Question 9

How can you remove carbon monoxide and other gaseous pollutants from internal combustion engines?

Answer 9

By using a catalytic converter.
This uses a rhodium catalyst to convert harmful products into more stable products such as CO2 or H2O

Question 10

What is the equation to show how CaO removes SO2 from flue gases ?

Answer 10

CaO + 2H2O + SO2 + 1/2 O2 => CaSO4•2H2O

Question 11

What is the equation to show how calcium carbonate removes SO2 from flue gases?

Answer 11

CaCO3 + SO2 + 1/2 O2 => CaSO4 + CO2

Question 12

What is the complete combustion equation for CH4 (methane)?

Answer 12

CH4 + O2 => CO2 + 2H2O

Question 13

What is the incomplete combustion equation for CH4 ( methane) ?

Answer 13

CH4 + 1 1/2 O2 => CO + 2H2O

Question 14

Why does incomplete combustion happen ?

Answer 14

Not enough O2

Question 15

Why do we use calcium oxide (CaO) to remove SO2 from flue gases ?

Answer 15

CaO is basic so will react with acid.
It’s an acid - base reaction

Question 16

What is CaSO4 (calcium sulphate ) also known as and what can it be used for?

Answer 16

-Gypsum
- Used for plastering

Question 17

What is CaSO4 (calcium sulphate ) also known as and what can it be used for?

Answer 17

-Gypsum
- Used for plastering

Question 18

What catalyst would you use in a catalytic converter ?

Answer 18

Platinum (Pt) or Rhodium (Rh)

Question 19

What is the equation for the chlorination of methane ( chlorine reacting with methane ) ?

Answer 19

CH4 + Cl2 => CH3Cl + HCl

Question 20

What is the initiation step of the chlorination of methane ?

Answer 20

Cl2 => 2Cl•

Question 21

What are the propagation steps for the chlorination of methane ?

Answer 21

Cl• + CH4 => •CH3 + HCl
•CH3 + Cl2 => CH3Cl + Cl•

Question 22

What is the termination step for the chlorination of methane ?

Answer 22

either
•CH3 + •CH3 => C2H6
•CH3 + Cl• => CH3Cl

Question 23

What is the general formula for a cycloalkane ?

Answer 23

CnH2n

Question 24

What are the dangers of producing carbon monoxide ( CO) ?

Answer 24

• Poisonous as it bonds to haemoglobin in the blood and prevents oxygen bonding.

Question 25

What is the danger of the production of soot ?

Answer 25

Can cause breathing problems , make buildings dirty and clog up engines

Question 26

How do we get photochemical smog?

Answer 26

When solid carbon particulates ( formed from incomplete combustion of hydrocarbons) and ozone mix together