Cracking hydrocarbons
The breaking down of large hydrocarbon molecules into smaller, more useful hydrocarbon molecules by vaporising them and passing them over a hot catalyst. is a process in which long chain A compound that contains hydrogen and carbon only. A collection of two or more atoms held together by chemical bonds. are broken down into smaller, more useful hydrocarbon molecules.
The original starting hydrocarbons are Saturated hydrocarbon. A compound of hydrogen and carbon only, with no C=C bonds.. The products of cracking include alkanes and Unsaturated hydrocarbon with a double bond between the carbon atoms., members of a different A 'family' of organic compounds that have the same functional group and similar chemical properties. .
An alkene is a hydrocarbon that contains a carbon-carbon double bond.
Hexane can be cracked to form butane and ethene:
hexane 鈫 butane + ethene
C6H14 鈫 C4H10 + C2H4
The longer alkanes are heated and their vapours are passed over a hot A substance that changes the rate of a chemical reaction without being changed by the reaction itself.. This causes A bond between atoms formed when atoms share electrons to achieve a full outer shell of electrons. to break and reform. The slideshow describes this process.
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Reasons for cracking
Cracking is important for two main reasons:
- It helps to match the supply of In fractional distillation, such as that of crude oil, the different parts of the original mixture are called fractions. The substances in each fraction have similar boiling points to each other. with the demand for them. The supply is how much of a fraction an oil refinery produces. The demand is how much of a fraction customers want to buy. In fractional distillation a mixture of several substances, such as crude oil, is distilled and the evaporated components are collected as they condense at different temperatures. of Mixture of hydrocarbons, mainly alkanes, formed over millions of years from the remains of ancient dead marine organisms. usually produces more of the larger hydrocarbons than can be sold, and less of the smaller hydrocarbons than customers want. Smaller hydrocarbons, such as petrol, are more useful as Material that is used to produce heat, like coal, oil or gas. than larger hydrocarbons. Since cracking converts larger hydrocarbons into smaller hydrocarbons, the supply of fuels is improved. This helps to match supply with demand.
- It produces alkenes. Alkenes are more reactive than alkanes. They are used as A raw material used to provide reactants for an industrial reaction. for the Substance made from crude oil using chemical reactions. industry.