Cracking

In-depth explanation of Cracking

Cracking is the breaking of large hydrocarbon molecules into smaller, more useful alkanes and alkenes. Thermal cracking uses high temperature and pressure, while catalytic cracking uses zeolite catalysts at about 500 degrees Celsius and lower pressure. The reaction proceeds through free radicals in thermal cracking and through carbocations in catalytic cracking. It is essential in refineries because the demand for smaller molecules such as petrol and ethene is greater than the supply from crude oil.

Going deeper: Cracking

Key ideas: Large alkanes are broken into smaller alkanes and alkenes. Thermal cracking uses 450 to 750 C and high pressure by a radical mechanism giving alkenes; catalytic cracking uses zeolite at about 500 C through carbocations and gives branched and aromatic products, raising octane number. Hydrocracking adds hydrogen. Example: C10H22 gives C8H18 plus C2H4.

Common mistakes and connections: Students forget that products must conserve atoms, so one alkane gives one alkane plus one alkene. Another mistake is equating cracking with reforming, which rearranges molecules without reducing size. Links to petroleum refining, polymer feedstocks (ethene, propene) and carbocation rearrangement.

Visualization of Cracking

Cracking splits decane into octane plus ethene (C10H22 gives C8H18 + C2H4); the smaller products boil at much lower temperatures. The interactive lesson shows this as a live animation or chart.

Worked example and use case

Decane cracks to give octane and ethene, C10H22 giving C8H18 plus C2H4.

Where Cracking fits in Organic Chemistry

Cracking is topic 44 of 148 in Organic Chemistry.

Related topics

• Reaction Types in Organic ChemistryBeginner
• Free Radical HalogenationIntermediate
• Combustion of HydrocarbonsBeginner
• Fractional Distillation of Crude OilBeginner
• Octane NumberIntermediate
• Electrophilic AdditionIntermediate

Browse all 148 topics in Organic Chemistry