alkanes 3.3.2 in paper 2&3

Question 1

what’s thermal cracking?

Answer 1

• the heating of alkanes to a high temperature.
• forms free radicals.

Question 2

what is catalytic cracking?

Answer 2

• takes place at lower temperatures
• uses a zeolitte catalyst
• products are separated using fractional distillation

Question 3

what are economic reasons for cracking?

Answer 3

• The petroleum fractions with shorter C chains are in more demand than larger fractions.
• To make use of excess larger hydrocarbons and to supply demand for shorter ones, longer hydrocarbons are cracked.
• The products of cracking are more valuable than the starting materials

Question 4

how can SO2 be removed?

Answer 4

SO2 can be removed from the waste gases from furnaces (e.g. coal fired power stations) by flue gas desulfurisation. The gases pass through a scrubber containing basic calcium oxide which reacts with the acidic sulfur dioxide in a neutralisation

Question 5

what do catalytic converters do?

Answer 5

These remove CO, NOx and unburned hydrocarbons (e.g. octane, C8H18) from the exhaust gases, turning them into ‘harmless’ CO2, N2 and H2O.
2 CO + 2 NO  2 CO2 + N2
C8H18 + 25 NO  8 CO2 + 12½ N2 + 9H2O

Question 6

whats the greenhouse effect?

Answer 6

UV wavelength radiation passes through the atmosphere to the Earth’s surface and heats up Earth’s surface.
The Earth radiates out infrared long wavelength radiation.
The C=O Bonds in CO2 absorb infrared radiation so the IR radiation does not escape from the atmosphere.
This energy is transferred to other molecules in the atmosphere by collisions so the atmosphere is warmed.