Alkanes
Saturated hydrocarbons
Unreactive – do burn and react with halogens
o C-C backbone very strong
o Non-polar
Used as fuels
State at Room Temperature
C1-C4 – gaseous
C5-C17 – liquid
C18+ - waxy solids
Insoluble in water
Boiling Points
Longer chain molecules have larger boiling points due to stronger van der waals forces between
the molecules as there are more electrons in the molecules
Branched molecules have smaller boiling points than their straight chain counterparts as there
are weaker van der waals forces between the molecules as they cannot pack as close together
as in straight chain molecules
Fractional Distillation
Petroleum/crude oil is a mixture consisting of mainly alkane hydrocarbons that can be separated
by fractional distillation
Crude oil is vapourised
Passed into column where temperature is highest at the bottom and coolest at the top
As vapour rises, it cools and condenses
The condensed vapour is collected as it condenses
The vapours condense at different heights due to the different boiling points of the various
hydrocarbons
The collected hydrocarbons are known as fractions – hydrocarbons with similar boiling points
As carbon chains get longer, molecules:
o Have higher boiling points
o Are more viscous
o Are less volatile
o Are harder to ignite
Residue is sent to vacuum distillation as their boiling points at atmospheric pressure would
cause them to decompose
Cracking
Higher demand for short chain than long chain hydrocarbons, but higher supply of long chain
hydrocarbons and shortfall in supply of short chain hydrocarbons
Saturated hydrocarbons
Unreactive – do burn and react with halogens
o C-C backbone very strong
o Non-polar
Used as fuels
State at Room Temperature
C1-C4 – gaseous
C5-C17 – liquid
C18+ - waxy solids
Insoluble in water
Boiling Points
Longer chain molecules have larger boiling points due to stronger van der waals forces between
the molecules as there are more electrons in the molecules
Branched molecules have smaller boiling points than their straight chain counterparts as there
are weaker van der waals forces between the molecules as they cannot pack as close together
as in straight chain molecules
Fractional Distillation
Petroleum/crude oil is a mixture consisting of mainly alkane hydrocarbons that can be separated
by fractional distillation
Crude oil is vapourised
Passed into column where temperature is highest at the bottom and coolest at the top
As vapour rises, it cools and condenses
The condensed vapour is collected as it condenses
The vapours condense at different heights due to the different boiling points of the various
hydrocarbons
The collected hydrocarbons are known as fractions – hydrocarbons with similar boiling points
As carbon chains get longer, molecules:
o Have higher boiling points
o Are more viscous
o Are less volatile
o Are harder to ignite
Residue is sent to vacuum distillation as their boiling points at atmospheric pressure would
cause them to decompose
Cracking
Higher demand for short chain than long chain hydrocarbons, but higher supply of long chain
hydrocarbons and shortfall in supply of short chain hydrocarbons
