Alkanes and Their Reactions

Comprehensive vocabulary flashcards covering the properties, naming, industrial processing, environmental impact, and reaction mechanisms of alkanes based on the lecture notes.

Alkanes

Saturated hydrocarbons that contain only carbon-carbon and carbon-hydrogen single bonds.

General molecular formula for chain alkanes

$$C_nH_{2n+2}$$

General molecular formula for ring alkanes

$$C_nH_{2n}$$

Unbranched alkanes (straight chains) bond angle

The C-C-C angle in these chains is $109.5^{\circ}$, meaning the chains are not actually straight.

Isomerism

Compounds with the same molecular formula but different structural arrangements, which increase in number as the carbon chain length increases.

Van der Waals forces

Weak intermolecular forces that act between almost non-polar alkane molecules; their strength increases as the molecule size increases.

Boiling point trend in alkanes

Boiling points increase as chain length increases due to increasing van der Waals forces.

Melting points of branched alkanes

Branched chains have lower melting points than straight chains with the same number of carbons because they cannot pack together as closely.

Solubility of alkanes

Insoluble in water because water's hydrogen bonds are stronger than the van der Waals forces in alkanes, though they mix with other non-polar liquids.

Crude oil

A non-renewable fossil fuel mixture mainly composed of branched and unbranched alkanes, formed by the breakdown of plant and animal remains.

Fractional distillation

A physical process used to separate crude oil into fractions of hydrocarbons with similar chain lengths and boiling points.

Fractionating tower temperature gradient

The tower is cooler at the top and hotter at the bottom to allow vapours to condense at trays corresponding to their specific boiling points.

Bitumen (Tar)

The thick residue that collects at the base of the fractionating tower used for road surfacing.

Fracking (Hydraulic fracturing)

The process of extracting natural gas trapped in shale rock by injecting pressurized water, sand, and chemicals to break the rock.

Industrial cracking

The process of breaking down longer, less useful hydrocarbon chains into shorter, more valuable ones and alkenes.

Thermal cracking

Cracking at high temperatures ($700-1200\,K$) and high pressure (up to $7000\,kPa$) that produces a high proportion of alkenes.

Catalytic cracking

Cracking at a lower temperature (approx. $720\,K$) and lower pressure using a zeolite catalyst; it produces branched alkanes, cycloalkanes, and aromatic compounds.

Zeolite catalyst

A catalyst used in cracking consisting of silicon dioxide and aluminium oxide (aluminosilicates) with a honeycomb structure for high surface area.

Fuels

Substances that release heat energy when they undergo combustion.

Complete combustion of alkanes

Alkanes burn in a plentiful supply of oxygen to form carbon dioxide ($CO_2$) and water ($H_2O$).

Incomplete combustion

Combustion in a limited supply of oxygen that produces poisonous carbon monoxide ($CO$) or carbon (soot).

Photochemical smog

A mixture containing airborne particles and ground-level ozone caused by the reaction of sunlight, nitrogen oxides ($NO_x$), and volatile organic compounds.

Acid rain contributors

Sulfur dioxide ($SO_2$) and nitrogen oxides ($NO_x$) which react in the atmosphere to form sulfuric acid and nitric acid.

Flue gas desulfurisation

The process of removing sulfur dioxide from power station emissions using a slurry of calcium oxide (lime) or calcium carbonate (limestone).

Catalytic converter

A car exhaust device using platinum and rhodium catalysts to convert $CO$, $NO_x$, and unburnt hydrocarbons into $N_2$, $CO_2$, and $H_2O$.

Greenhouse effect

The trapping of infrared radiation (heat) by gases like carbon dioxide ($CO_2$), methane ($CH_4$), and water vapour ($H_2O$) in the atmosphere.

Carbon neutral

Activities that result in no net carbon dioxide emissions overall.

Free radical

A highly reactive species with an unpaired electron, formed when a covalent bond breaks homolytically.

Initiation (Free-radical substitution)

The first step where a halogen bond is broken by a quantum of ultraviolet (UV) light to form two free radicals.

Propagation (Free-radical substitution)

A two-stage chain reaction step that produces a stable compound and a new free radical to continue the process.

Termination (Free-radical substitution)

The step where two free radicals react together to form a stable compound, ending the chain reaction.

CFCs (Chlorofluorocarbons) and Ozone

Compounds that release chlorine free radicals in the stratosphere under UV radiation, which then catalyze the breakdown of ozone ($O_3$) into oxygen ($O_2$).