Alkanes, Fractional Distillation, and Cracking

Vocabulary flashcards covering alkane isomerism, physical properties, fractional distillation, thermal and catalytic cracking, and environmental impacts of crude oil impurities.

2,2-Dimethylpropane

A branched alkane isomer of pentane consisting of a central carbon atom bonded to four methyl groups.

2-Methylbutane

A branched alkane isomer of pentane containing a four-carbon main chain with one methyl branch on the second carbon atom.

Pentane

A straight-chain alkane with five carbon atoms and the chemical formula $C_5H_{12}$.

Electronegativity

The power of an atom to attract electron density in a covalent bond.

Non-polar Molecule

A molecule formed between atoms with similar electronegativity values, resulting in an even distribution of electron density.

Polar Molecule

A molecule characterized by a difference in electronegativity across its bonded atoms.

Van der Waals Forces

Weak intermolecular forces of attraction active between non-polar alkane molecules.

Alkane Boiling Point Trends

Boiling point increases with larger molecular size due to stronger Van der Waals forces, but decreases with chain branching because branched molecules cannot pack close together.

Alkane Solubility

Alkanes are insoluble in water because water molecules are held by strong hydrogen bonds that are stronger than Van der Waals forces, but they mix readily with other non-polar liquids.

Crude Oil

A mixture composed mostly of alkanes formed over millions of years by the decay of plant and animal remains under high temperatures and pressures.

Fractional Distillation

A process used to separate crude oil into useful fractions based on boiling points using a temperature gradient in a fractionating column.

Fractionating Column Temperature Gradient

The temperature profile inside a fractionating column, which is hot at the bottom ($400^\circ\text{C}$) and cool at the top ($20^\circ\text{C}$).

Thermal Cracking

An industrial reaction carried out at high temperatures ($70\text{ to }1200\,\text{K}$ or $900^\circ\text{C}$) and high pressure ($7000\,\text{kPa}$ or $70\,\text{atm}$) without a catalyst, producing high proportions of alkenes.

Free Radicals

Highly reactive carbon chain fragments with an unpaired electron formed during thermal cracking when C-C bonds break homolytically.

Catalytic Cracking

A cracking process operating at lower temperature ($720\,\text{K}$ or $450^\circ\text{C}$) and lower pressure ($1\text{ to }2\,\text{atm}$) using a zeolite catalyst to produce motor fuels.

Zeolites

Acidic aluminosilicate catalysts composed of silicon dioxide and aluminium oxide with a honeycomb structure and a huge surface area.

Sulphur Dioxide Formation

The combustion of sulphur impurities present in crude oil, represented by the chemical equation $S + O_2 \rightarrow SO_2$.

Sulphur Trioxide Formation

The oxidation of sulphur dioxide high in the atmosphere, given by the chemical equation $2SO_2 + O_2 \rightarrow 2SO_3$.

Sulphuric Acid Formation

The reaction of sulphur trioxide with atmospheric water to form acid rain, represented by $SO_3 + H_2O \rightarrow H_2SO_4$.