Chemistry125 views·Updated Jun 4, 2026·2 pages

Understanding Alkanes and Haloalkanes: Fractional Distillation and Cracking Explained

Aasiyah Rahman@aasiyahrahman

Diving into alkanes and haloalkanes, this topic explores how crude...

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# Alkanes and Haloalkanes

1 Alkanes - Fractional distillation/Cracking

Refining crude oil

Petroleum = mixture consisting main only alkane

Crude Oil Refining and Cracking

Ever wondered how we get petrol from crude oil? It starts with fractional distillation, where crude oil (mainly alkane hydrocarbons) is heated and passed through a column. Different fractions condense at different heights based on their boiling points. Larger hydrocarbons have higher boiling points due to stronger van der Waals forces, so they settle in lower fractions.

When there's too much of the larger hydrocarbons and not enough of the smaller ones, we use cracking to break C-C bonds. This converts large hydrocarbons into smaller, more valuable products. Thermal cracking uses high temperatures $400-900°C$ and pressure to produce mainly alkenes for polymers, while catalytic cracking uses a zeolite catalyst at lower temperatures (450°C) to produce branched and cyclic hydrocarbons for cleaner-burning motor fuels.

The combustion of alkanes releases heat energy, making them excellent fuels. Complete combustion (with excess oxygen) produces CO₂ and H₂O, while incomplete combustion produces less energy and forms carbon monoxide, soot, and water. This is why proper air flow is crucial when burning fuels.

Did you know? Branched and cyclic hydrocarbons have higher octane numbers, making them better for engines as they burn more cleanly and efficiently.

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Environmental Impact of Combustion

Burning hydrocarbons isn't without consequences. Nitrogen oxides form when atmospheric nitrogen reacts with oxygen at high temperatures inside engines, creating toxic compounds that contribute to acid rain. Similarly, sulphur impurities in fuels produce SO₂ when burned, which dissolves in atmospheric water to form acid rain.

To combat these pollutants, modern vehicles use catalytic converters containing precious metals like platinum and palladium. These converters have a honeycomb structure coated with catalysts that transform harmful exhaust gases (CO, NOₓ, unburned hydrocarbons) into less harmful substances like CO₂, N₂, and H₂O.

The combustion of fossil fuels has significantly increased greenhouse gases like CO₂ in our atmosphere. These gases trap Earth's radiated infrared energy, leading to global warming. Carbon monoxide (toxic), carbon dioxide (greenhouse gas), unburnt hydrocarbons (smog formation), and soot (respiratory problems and global dimming) are all pollutants resulting from hydrocarbon combustion.

Important connection: Understanding the chemistry of fuel combustion helps explain why electric vehicles and renewable energy sources are becoming increasingly important in combating climate change.

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Chemistry125 views·Updated Jun 4, 2026·2 pages

Understanding Alkanes and Haloalkanes: Fractional Distillation and Cracking Explained

Aasiyah Rahman@aasiyahrahman

Diving into alkanes and haloalkanes, this topic explores how crude oil is processed into useful products and the environmental impacts of hydrocarbon combustion. Understanding these concepts is essential for chemistry students as they connect directly to energy production, environmental concerns,...

of 2

Crude Oil Refining and Cracking

Did you know? Branched and cyclic hydrocarbons have higher octane numbers, making them better for engines as they burn more cleanly and efficiently.

of 2

Environmental Impact of Combustion

Important connection: Understanding the chemistry of fuel combustion helps explain why electric vehicles and renewable energy sources are becoming increasingly important in combating climate change.