3.3.2 Alkanes

Question 1

free radical substitution of ozone (Cl + O3)

Answer 1

Cl· + O3 -> ClO· + O2
ClO· + O3 -> Cl· + 2O2
2O3 -> 3O2

Question 2

State why the ozone layer is beneficial for living organisms.

Answer 2

absorbs harmul UV

Question 3

State how chlorofluorocarbons (CFCs) form chlorine atoms in the
upper atmosphere.

Answer 3

C-Cl bonds broken homolytically

Question 4

define petrol fraction

Answer 4

mixture of hydrocarbons with similar boiling points

Question 5

difference between thermal cracking and catayltic cracking

Answer 5

THERMAL:
- usually produces alkanes + alkenes; high temperatures (1200K) and pressures (7000 kPa)

CATALYTIC:
- usually produces aromatic compounds
- high temperatures + moderate pressure
- zeolite catalyst

Question 6

describe the process of the fractional distillation of crude oil

Answer 6

• crude oil is heated and vaporised (M1)
• vapour is fed into a fractionating column (M2); has a temperature gradient -> hotter at the bottom and cooler at the top (M3)
• hydrocarbons condense at different points depending on their boiling point (M4)
• longer-chain hydrocarbons condense near the bottom; each fraction contains hydrocarbons with similar boiling points
• fractions are collected + used for different purposes