Cracking

Question 1

Define what is meant by cracking?

Answer 1

Large fractions of crude oil broken down into smaller fractions using heat

Question 2

Why do oil companies need to crack ‘heavy fractions’ ?

Answer 2

Smaller chain molecules are in higher demand as theyre more useful

Question 3

What are the 2 types of cracking?

Answer 3

Thermal and catalytic

Question 4

What similarity do both thermal and catalytic cracking share?

Answer 4

• both involve breaking of C - C bonds to smaller molecules
• C - C bonds are weaker than C - H bonds, so break easier when heated

Question 5

Describe the conditions of thermal cracking

Answer 5

• bonds broken using high temp (700 - 1200 K)
• high pressure (kPa)
• alkenes kept in these conditions for one second

Question 6

State the type of cracking that produces a high % of alkenes + give 2 conditions

Answer 6

Thermal cracking
High temp and pressure

Question 7

Most thermal cracking reactions involve formation of what?

Answer 7

• one small alkane
• two or more alkenes

Question 8

A long chain hydrocarbon is cracked to produce hexane, butene and ethene. What type of cracking is this?

Answer 8

Two alkenes are made so this is thermal cracking

Question 9

Describe conditions of catalytic cracking

Answer 9

• bonds broken at high temp (720 K - generally lower than thermal cracking)
• slight pressure
• zeolite catalyst - lower cost, lower temp

Question 10

State the type of cracking that produces a high % of branched alkanes and cycloalkanes + give 2 conditions

Answer 10

Catalytic cracking
Zeolite catalyst and temp of 720 K

Question 11

What are the uses of cycloalkanes?

Answer 11

Cycloalkanes are widely used in motor fuels and aromatic hydrocarbons such as benzene which have a variety of uses