Answer:
Properties of fractions
Properties of fractions
Each crude oil fraction contains a mixture of hydrocarbons. The hydrocarbons in a fraction are mostly hydrocarbons called alkanes. They have similar (but not identical):
- numbers of hydrogen and carbon atoms in their molecules
- boiling points
- ease of ignition
- viscosity
For example, the gases fraction contains hydrocarbons with one to four carbon atoms. These have:
- boiling points below room temperature
- they are very flammable
- have a low viscosity
The hydrocarbons in different fractions differ in these properties. For example, the bitumen fraction contains hydrocarbons with more than 35 carbon atoms. These have:
- boiling points well above room temperature
- are very difficult to ignite
- have a high viscosity
Hydrocarbon fuels can undergo complete combustion or incomplete combustion, depending on the amount of oxygen available.
Complete combustion
Complete combustion of a hydrocarbon fuel happens when there is a good supply of air. Carbon and hydrogen atoms in the fuel react with oxygen in an exothermic reaction:
- carbon dioxide and water are produced
- the maximum amount of energy is given out
- In a Bunsen burner, this occurs when the air hole is fully open.
