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CIE A Level Chemistry复习笔记3.2.1 Alkanes
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A-level课程
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教材笔记
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福利干货
Date: 2022年8月12日 下午3:46
Production of Alkanes: Hydrogenation & Cracking
Alkanes are hydrocarbons that can be produced by the addition reaction of hydrogen to an alkene or by cracking of longer alkane chains
Production of alkanes from addition reactions
Alkenes are unsaturated organic molecules and contain C-C double bonds
When hydrogen gas and an alkene are heated and passed over a finely divided Pt/Ni catalyst, the addition reaction produces an alkane:
The Pt/Ni catalyst is finely divided to increase its surface area and therefore increase the rate of reaction
Eg. butane from 1-butene
Hydrogen gas is added to 1-butene which are then heated and passed over a Pt/Ni catalyst to produce butane
The addition reaction of alkenes with hydrogen is called hydrogenation
Hydrogenation is often used in the manufacture of margarine from vegetable oil
Vegetable oil is an unsaturated organic molecule with many C-C double bonds
When these are partially hydrogenated, their hydrocarbon chains become straighter
This raises the melting point of the oils which is why margarine is a soft solid and vegetable oil a liquid at room temperature
Production of alkanes from cracking
In cracking large, less useful hydrocarbon molecules found in crude oil are broken down into smaller, more useful molecules
The large hydrocarbon molecules are fed into a steel chamber and heated to a high temperature and then passed over an aluminium oxide (Al2O3) catalyst
The chamber does not contain any oxygen to prevent combustion of the hydrocarbon to water and carbon dioxide
When a large hydrocarbon is cracked, a smaller alkane and alkene molecules are formed
Eg. octane and ethene from decane
Long hydrocarbons are cracked by heating them and using aluminium oxide catalyst into smaller hydrocarbons and an alkene
Exam Tip
Remember that hydrogenation is an exothermic reaction and cracking is an endothermic reaction.
转载自savemyexams
Previous post: CIE A Level Chemistry复习笔记3.1.13 Isomers of Organic Compounds
Next post: CIE A Level Chemistry复习笔记3.2.2 Combustion & Free Radical Substitution of Alkanes
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