Cracking Hydrocarbons Grommit! Starter Write a definition for the following terms: a) Hydrocarbon b) Alkane c) Alkene Alkenes all have a carbon-carbon double bond in its molecule. Extension: State whether they are alkenes or alkanes. List some fractions obtained from crude oil. C H

Learning Objectives Learning outcomes By the end of the lesson you should know: Cracking is the thermal decomposition of large chain hydrocarbons to smaller chain hydrocarbons To be able to describe the difference between alkene and alkane. Learning outcomes By the end of the lesson you should be able to: Describe what cracking is Explain that the products of cracking are used as fuels and to make plastics Describe what alkenes are and how they are represented

Break the chocolate into edible chunks (more useful pieces) A large chocolate bar can’t be eaten until it is cracked (broken down). What can we do? Break the chocolate into edible chunks (more useful pieces) Splints To get it in my mouth

How do we Crack a Molecule? In a School Lab High temperatures and a catalyst. In Oil Industry High temperatures, a catalyst and high pressure because it is more efficient. The temperature and pressure are carefully selected to give us a high % of the length of hydrocarbon we are wanting (e.g. hydrocarbons with 5-10 carbon atoms)

Example During cracking, the hydrocarbons are vaporised and passed over the catalyst at 500ºC. The temperature and pressure used for the cracking process are selected to give a high% of hydrocarbons with 5-10 carbon atoms. These are the hydrocarbons needed for petrol.

Catalytic Cracking in Industry Large hydrocarbons are broken into smaller molecules using heat and a catalyst. The reaction is an example of thermal decomposition Catalytic cracker Heat to vaporise Distillation tower pressure Smaller molecules Big Molecules Molecules break up

Cracking Example C10H22 C2H4 + C3H6 + C5H12 Decane  Ethene + Propene + Pentane As a large molecule is broken into smaller ones using heat, this is another example of a thermal decomposition reaction. 800°C catalyst Used to make plastics (polymers) Polyethene / polypropene Used in petrol

How would we test the gas? And what for? Gas collecting over water. 2 Tubes to collect Boiling tube containing liquid paraffin and catalyst Bromine water Stopper to seal boiling tube of gas How would we test the gas? And what for?

Cracking Hydrocarbons Grommit! Cat Cracker C H

Products of Cracking Cracking produces saturated hydrocarbons (alkanes) which are used as fuels and also unsaturated hydrocarbons (alkenes) used as plastics

How many hydrogen? How many carbons? 16 7 2 5 4 12

Which of these liquids has the longest hydrocarbon chains? Viscosity Some hydrocarbons have long, flexible molecules. The longer the molecule, the more tangled they can become with other molecules. This makes the liquid thicker (more viscous) and less easy to pour. Motor oils have a range of viscosities displayed on their containers. They are written as numbers with a ‘W’ after them Longer chains more tangled the molecule Which of these liquids has the longest hydrocarbon chains?

The Reactivity of Alkenes The carbon double bond of alkenes is a target for reactions. One of the two bonds can easily be broken. This allows the carbon atom to react with other atoms.

The Reactivity of Alkenes Propene C3H6 (colourless gas) Bromine Solution Br2 (orange /yellow) Dibromopropane CH2Br-CHBr-CH3 (colourless liquid) When propene (C3 alkene) and bromine react they produce a saturated compound because it contains only carbon- carbon single bonds.

Definition of Catalytic Cracking Write a paragraph explaining how cracking occurs. . Include the following keywords. Hydrocarbons, Alkanes, Catalyst, Cracking, Thermal Decomposition, Alkene Extension: Give an example, word and symbol inc catalyst and conditions used). Cracking is the name given to the breaking up of large hydrocarbons molecules into smaller and more useful bits. Cracking involves heating hydrocarbons (alkanes) until they vaporise then passing them over a hot catalyst. This process is calles thermal decomposition and it produces an alkane and an alkene.

Learning Objectives Learning outcomes By the end of the lesson you should know: Cracking is the thermal decomposition of large chain hydrocarbons to smaller chain hydrocarbons To be able to describe the difference between alkene and alkane. Learning outcomes By the end of the lesson you should be able to: Describe what cracking is Explain that the products of cracking are used as fuels and to make plastics Describe what alkenes are and how they are represented