Key Stage 4
Meaning
Cracking is a Thermal Decomposition process in which large hydrocarbon molecules are broken into smaller hydrocarbon molecules.
About Cracking
- Cracking is often done because Crude Oil contains more large hydrocarbon molecules than can be used and not enough short hydrocarbon molecules than are needed.
- When Crude Oil fractions are cracked the long alkanes are broken down into smaller alkanes and alkenes.
- Cracking is done at very high temperatures (500°C) and uses either a catalyst to aid the reaction or steam.
- When an alkane is cracked into smaller pieces there are not enough Hydrogen [[atom]s to produce two saturated hydrocarbons. One of the hydrocarbons must be unsaturated and therefor will have a double bond.
Examples
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| If butane were cracked. | An alkane and an alkene are produced. | |||
Cracking a hydrocarbon can produce many possible products:
Hexadecane → Decane + Hexene <chem>C16H34 -> C10H22 + C6H12</chem>
Hexadecane → Decane + Butene + Ethene <chem>C16H34 -> C10H22 + C4H8 + C2H4</chem>
Decane → Pentane + Pentene <chem>C10H34 -> C5H12 + C5H10</chem>
Decane → Hexane + Butene <chem>C10H34 -> C6H14 + C4H8</chem>