Cracking and Polymers

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• Obtaining useful substances from crude oil

• Hydrocarbons can be cracked to make smaller and more useful molecules.

• The process CRACKINGinvolves heating the hydrocarbons to vaporise them

• The vapour then passes over a hot catalyst or mixed with steam and then heated so a thermal decomposition reaction occurs.

• The products of cracking include alkanes and unsaturated hydrocarbons alkenes.

• The General formula for the homologous series of alkanes is CnH2n

• Unsaturated has at least one double covalent bond between the carbons.

• Unsaturated hydrogen molecules can be shown in the following forms:C3H6

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• You can test a alkene by adding bromine water.Orange to colourless.

• some products of cracking are useful as fuels.

• Ethanol can be produced by reacting ethene with steam in the presence of a catalyst

• Polymers

• In polymerisation many small molecules (monomers) are joined together to form polymers

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• The properties of the polymer depend on what they are made from and the conditions under which they are made. Low density and High density poly(ethene) are produced using different catalysts and reactions conditions.

• Thermosetting polymers consist of cross links between the polymer chains so they don't melt when heated.

• Thermosoftening polymers consist of individual, tangled polymer chains.

• Polymers have many useful applications.

• New packaging methods Dental polymers waterproofing fabrics wound dressings Hydrogels

• Polymers are not biodegradable. so microbes can't break them down.

• plastic bags are being made from polymers and cornstarch so they break down more easily. Biodegradable bags are being made from cornstarch and are being developed.

• High density - few branches on polymer molecules Low density - many branches on the polymer molecule