12.1 - Modifications of alkanes by cracking

Question 1

Catalytic cracking conditions

Answer 1

Catalytic crackinguses a lower temperature (around 450oC) and slight pressure in the presence of a catalyst such as a zeolite or aluminium oxide to produce mainly aromatic hydrocarbons

Question 2

Thermal cracking conditions

Answer 2

Thermal crackingrequires high temperatures (up to 1000oC) and high pressure (up to 70 atmospheres) and produces alkanes and a lot of alkenes

Question 3

What is cracking used for and why is it used?

Answer 3

• Incrackingthese large, less useful hydrocarbon molecules found in crude oil are broken down into smaller, more useful molecules
• The large hydrocarbon molecules are fed into asteelchamberandheatedto a high temperature and then passed over analuminiumoxide(Al2O3) catalyst
• The chamber does not contain anyoxygento preventcombustionof the hydrocarbon to water and carbon dioxide
• When a large hydrocarbon is cracked, asmalleralkaneand one (or more)alkene molecules are formed

Question 4

What is crude oil

Answer 4

• Crude oil is amixtureof hydrocarbons containingalkanes,cycloalkanesandarenes(compounds with a benzene ring)