4 - 23 Crude oil
● ***Crude oil: mixture of hydrocarbons, formed from decayed organic matter; finite,
non-renewable source
How physical properties of hydrocarbons change with molecule
size
● As molecules become bigger (more carbon atoms),
- ***Boiling point increases - larger molecule, higher boiling point, as large
molecules are attracted to each other more strongly than smaller ones, more
energy is needed to break stronger intermolecular forces to produce widely
separated molecules in gas
- ***Less volatile (易揮發的) (for liquids) - bigger hydrocarbon, slower
evaporation at room temperature, as stronger intermolecular forces,
hydrocarbons do not turn into gas easily
- ***More viscous (粘性的), flow less easily (for liquids) - larger
molecules flow less easily due to stronger intermolecular forces
- Darker in colour
- Bigger hydrocarbons do not burn as easily as smaller ones (i.e.: lower
flammability)
Separation of crude oil
● ***Fractional distillation (分餾): separating crude oil into fractions, carried out in oil
refinery
● Crude oil is heated until boiled, and its vapours pass into fractionating column,
cooler at top, hotter at bottom, vapours rise up column, ***how far up column
particular hydrocarbon moves depends on its boiling point
1
, ●
●
2
● ***Crude oil: mixture of hydrocarbons, formed from decayed organic matter; finite,
non-renewable source
How physical properties of hydrocarbons change with molecule
size
● As molecules become bigger (more carbon atoms),
- ***Boiling point increases - larger molecule, higher boiling point, as large
molecules are attracted to each other more strongly than smaller ones, more
energy is needed to break stronger intermolecular forces to produce widely
separated molecules in gas
- ***Less volatile (易揮發的) (for liquids) - bigger hydrocarbon, slower
evaporation at room temperature, as stronger intermolecular forces,
hydrocarbons do not turn into gas easily
- ***More viscous (粘性的), flow less easily (for liquids) - larger
molecules flow less easily due to stronger intermolecular forces
- Darker in colour
- Bigger hydrocarbons do not burn as easily as smaller ones (i.e.: lower
flammability)
Separation of crude oil
● ***Fractional distillation (分餾): separating crude oil into fractions, carried out in oil
refinery
● Crude oil is heated until boiled, and its vapours pass into fractionating column,
cooler at top, hotter at bottom, vapours rise up column, ***how far up column
particular hydrocarbon moves depends on its boiling point
1
, ●
●
2
