C 7.1 Cracking

Question 1

What is cracking?

Answer 1

A process that breaks down long-chain hydrocarbons into shorter, more useful hydrocarbons.

Question 2

Why is cracking necessary?

Answer 2

To meet the high demand for short-chain hydrocarbons (for fuels) and alkenes (for making plastics).

Question 3

What are the conditions for cracking?

Answer 3

High temperature + catalyst → Catalytic cracking
High temperature + pressure → Thermal cracking

Question 4

What are the products of cracking?

Answer 4

Short-chain alkanes (useful fuels)
Alkenes (used to make polymers)

Question 5

What is an alkene?

Answer 5

A hydrocarbon with a carbon–carbon double bond (C=C)

Question 6

What is the general formula of an alkene?

Answer 6

CnH₂n

Question 7

How can alkenes be tested for?

Answer 7

By adding bromine water – it turns colourless if an alkene is present.

Question 8

What are the uses of alkenes?

Answer 8

Used to make polymers such as plastics through polymerisation.

Question 9

What is the main difference between alkanes and alkenes?

Answer 9

Alkanes: saturated (single bonds)
Alkenes: unsaturated (contain double bonds)

Question 10

Give an example of cracking:

Answer 10

Decane → pentane + propene + ethene
(a long-chain alkane breaks into a shorter alkane and alkenes)