Cracking and alkenes

Question 1

What is cracking?

Answer 1

A thermal decomposition reaction where long-chain hydrocarbons get split up.

Question 2

What are the 2 types of cracking?

Answer 2

Catalytic and steam.

Question 3

What is the process of catalytic cracking?

Answer 3

1) Long-chain hydrocarbons are heated until they vaporise into a gas

2) The vapour is passed over a hot, powdered aluminium oxide catalyst

3) This causes the long hydrocarbon chains to split apart into shorter ones

Question 4

What is the process of steam cracking?

Answer 4

Long-chain hydrocarbons are vaporised then mixed with steam and heated at high temperatures.

Question 5

Why is an alkene produced in cracking?

Answer 5

There aren’t enough hydrogen atoms to make two alkanes.

Question 6

What is an alkene?

Answer 6

An unsaturated hydrocarbon as it has a C=C double bond. Alkenes are more reactive than alkanes.

Question 7

What is the general formula for alkenes?

Answer 7

Cn H2n

Question 8

What are the first 4 alkenes?

Answer 8

Ethene C2 H4
Propene C3 H6
Butene C4 H8
Pentene C5 H10

Question 9

How can you distinguish between alkanes and alkenes?

Answer 9

By doing the bromine water test. Bromine water is orange and turns colourless when mixed with alkenes. The water stays orange when mixed with alkanes as alkanes are not reactive enough to make the water colourless.