Cracking

Question 1

What is cracking?

Answer 1

A method used to break long chain alkanes into shorter chain alkanes or alkenes

Question 2

Why do we want shorter chain alkanes/ alkenes?

Answer 2

Shorter chain hydrocarbons are more useful and in high demand whereas longer chain hydrocarbons are less useful so there is lots left over

Question 3

What are short chain alkanes used for?

Answer 3

Fuels

Question 4

What are short chain alkenes used for?

Answer 4

Polymers (plastics)

Question 5

What does cracking produce?

Answer 5

An alkane (or hydrogen) and an alkene

Question 6

Catalytic cracking

Answer 6

-ceramic wool soaked in liquid hydrogen
-catalyst (aluminium oxide/alumina or silicon dioxide/silica)
-both the catalyst and hydrocarbon are heated (≈500°c)
-gaseous product (short alkane or alkene)
-some oily liquid may form

Question 7

Steam cracking

Answer 7

-hydrocarbon is mixed with steam
-heat to a very high temperature
-cracking occurs, breaking apart the longer molecules into two shorter molecules