Problem The long chained hydrocarbons are not useful They are thick liquids or solids with high boiling points They do not catch fire very easily This means they are not good for fuels
Cracking We can break down long hydrocarbon chains into smaller more useful chains Would you rather have lots of individual bars of chocolate or only one big bar?
Cracking video http://www.youtube.com/watch?v=Ehcq4cAR kMI http://www.youtube.com/watch?v=Ehcq4cAR kMI
Cracking Theory Long hydrocarbon chains are vaporised and passed over a hot catalyst or mixed with steam It is heated to a high temperature The long chains are ‘cracked’ as thermal decomposition takes place The large chains split apart to form smaller more useful chains
Definitions Hydrocarbon Contains hydrogen and carbon only Vaporised Turned into a gas Catalyst Speeds up a reaction Thermal decomposition Break down of substance due to heat
Task Produce a comic strip for cracking alkanes using ALL the key words Passed over a catalyst Vaporised: turned from a liquid to a gas Thermal decomposition takes place (long chain breaks down) Smaller more useful chains produced Useless long chain hydrocarbon
Extension Draw and label the practical equipment used for cracking on page 75 How does the practical take place?
Plenary Summarise today’s learning in one sentence.