C7: Cracking and Alkenes

Question 1

What are some uses of crude oil in modern life?

Answer 1

The petrochemical industry uses some of the hydrocarbons from crude oil as feedstock to make new compound for use in things like polymers, solvents, lubricants and detergents.

Question 2

What is cracking?

Answer 2

A thermal decomposition reaction. Breaking molecules down by heating them.

Question 3

What is the process of cracking?

Answer 3

1) Heat Long chain hydrocarbons to vaporise them
2) Vapour passed over a hot powdered aluminium oxide catalyst
3) Long chain molecules split apart on the surface of the specks of catalyst - this is catalytic cracking

You can also crack hydrocarbons if you vaporise them, mix with steam and then heat to a very high temperature. This is steam cracking.

Question 4

As well as alkanes, what does cracking also produce?

Answer 4

Alkenes:
More reactive
Used as starting material when making lots of other compounds & can be used to make polymers

Question 5

How can bromine be used to rest for Alkenes?

Answer 5

1) When orange bromine water is added to an alkane, no reaction will happen - it’ll stay bright orange
2) When added to an Alkenes the bromine reacts to make a colourless compound - so the bromine water is decolourised

Question 6

What is an Alkene?

Answer 6

Unsaturated hydrocarbons
Double bonds - speed up reactions

Remember no carbons are lost.
When a double bond occurs, usually the one before only has one hydrogen molecule attached.
One will always be an alkene and one an alkane in a reaction.

Question 7

What’s the general formula for Alkenes?

Answer 7

CnHn+2