alkanes Flashcards
What are alkanes?
A homologous series of saturated hydrocarbons with the general formula CnH2n+2.
How do alkanes differ?
They differ by a CH2 group.
What type of bonds do alkanes have?
Every carbon has 4 single bonds.
What are cycloalkanes?
Saturated alkanes that are unreactive but can burn and react with halogens.
What type of intermolecular forces exist between alkane molecules?
Van der Waals forces.
What happens to the boiling point of alkanes as chain length increases?
Boiling point increases due to more van der Waals forces.
What effect do branches on isomers of alkanes have on boiling point?
More branches lower the boiling point due to weaker van der Waals forces.
As chain length increases, how do hydrocarbons change in terms of viscosity, flammability, and volatility?
They become more viscous, less flammable, and less volatile.
What is petroleum primarily made of?
A mixture of hydrocarbons, mostly alkanes.
At what temperature is crude oil vaporised for fractional distillation?
350°C.
What is the purpose of the fractioning column in fractional distillation?
To separate hydrocarbons based on differences in chain length and boiling point.
What are the main fractions obtained from fractional distillation of crude oil?
- Gases (C1-4)
- Petrol (C5-12)
- Naphtha (C7-14)
- Kerosene (C11-15)
- Gas Oil (C15-19)
- Mineral Oil (C20-30)
- Residue (C30-50)
What is cracking in the context of hydrocarbons?
The process of breaking C–C bonds in alkanes to produce shorter chain hydrocarbons.
What are the two types of cracking?
- Thermal cracking
- Catalytic cracking
What temperature is used in thermal cracking?
Up to 1000°C.
What temperature is typically used in catalytic cracking?
Around 450°C.
What catalyst is commonly used in catalytic cracking?
Zeolites.
What are the main products of cracking?
- Alkenes
- Motor fuels (aromatics, cyclic alkanes, branched alkanes)
What is the purpose of reforming in hydrocarbon processing?
To convert straight hydrocarbon chains into branched alkanes and cycloalkanes for more efficient burning.
What type of reaction occurs during the combustion of alkanes?
Exothermic reaction.
What is the equation for complete combustion of an alkane?
alkane + oxygen → carbon dioxide + water.
What is produced during incomplete combustion of an alkane?
- Carbon monoxide
- Carbon particulates (soot)
- Water
What are common pollutants from burning fossil fuels?
- Carbon dioxide
- Carbon monoxide
- Carbon particulates
- Unburned hydrocarbons
- Sulfur dioxide
- Nitrogen oxides
What problem is caused by carbon dioxide emissions?
Global warming.
How is carbon monoxide formed?
Incomplete combustion of fuels containing carbon.
What health issue does carbon monoxide cause?
It is poisonous and toxic.
How can sulfur dioxide be produced?
Burning fossil fuels containing sulfur impurities.
What environmental issue is caused by sulfur dioxide?
Acid rain.
What is the reaction for the formation of sulfuric acid from sulfur dioxide?
SO2 + H2O → H2SO4.
What is the overall reaction for the formation of nitrogen oxides?
N2 + O2 → 2NO.
What is the role of catalytic converters?
To reduce levels of polluting gases from petrol-engine cars.
What is a free radical?
A species with a lone/unpaired electron that is highly unstable.
What initiates the free radical mechanism?
UV light breaking a halogen molecule into two free radicals.
What happens during the propagation step of the free radical mechanism?
A radical reacts with a molecule to form a new radical and product.
What occurs during the termination step of the free radical mechanism?
Two radicals pair up to form a stable molecule.
