Cracking

what are the two types of cracking?

catalytic cracking

steam cracking

why is cracking useful?

because it yields shorter saturated alkanes and unsaturated alkenes which are more useful as shorter chain fuels are more flammable

what temperature does cracking occur at?

470-500 degrees celsius for catalytic

800 degrees celsius for steam

what type of reaction is cracking an example of?

a thermal decomposition reaction

how to carry out catalytic cracking?

1. heat long chain alkane and vaporise it

2. pass the vapour over hot powdered aluminium oxide as a catalyst

3. as it passes over the powder and comes into contact with the powder the long alkane will split apart into two smaller hydrocarbons : a shorter chain saturated alkane and a shorter chain unsaturated alkene

why does cracking always produce one alkane and alkene?

because when a long chain alkane is cracked there aren’t enough hydrogen atoms to make two alkanes

how to carry out steam cracking

1. heat the long chain alkane and turn it into a gas (vaporise)

2. mix the vaporised alkane with steam and heat it to a very high temperature causing the long alkane to split apart into a shorter chain saturated alkane and unsaturated alkene

3. use a high temp of 800 degrees celsius