higher / lower / more / less

Hydrocarbons with different length chains have different properties, so can be used for different things. 

Shorter chain alkanes have melting and boiling points, so are flammable, and volatile. 

smaller / larger

Cracking is the process in which chain hydrocarbons are split into , more useful hydrocarbons.

Catalytic cracking 

1. First, some long chain alkanes are until they vaporise into a
2. Then they're passed over a hot, powdered oxide catalyst 
3. This breaks the long chain alkanes into a chain alkane and an

How is steam cracking different to catalytic cracking?

low / high / steam / catalyst / rate

Steam cracking is different because there is no involved. Instead the vaporised long chain alkane is mixed with at very temperatures.

carbon / hydrogen / alkane

When a long chain is cracked, there aren't enough atoms to make two alkanes. Hence, cracking will always produce one alkane and one alkene. (Alkenes are hydrocarbons with a double bond between two carbon atoms).

Introduction to alkenes

saturated / unsaturated / homologous / carbon / hydrogen

1. Alkenes are similar to alkanes. Alkenes are also hydrocarbons and also an example of a series.
2. The difference is that alkenes have a double bond between two atoms, whereas alkanes only have single bonds.
3. Another way to express the presence of the double bond between two carbon atoms is to say that alkenes are ''.

Bromine test for alkenes

chlorine / bromine / iodine / orange / blue / colourless

The test to distinguish between alkanes and alkenes is the water test.

Bromine water (just bromine dissolved in water) by itself is an colour. But when it's mixed with alkenes, all of the bromine will react, and so the solution loses its orange colour, and turns . 

This doesn't happen when bromine water is mixed with alkanes, because alkanes are not reactive enough to react with bromine water. So when mixed with an alkane, the solution will stay orange.