Year 10- Hydrocarbons

Crude Oil:

• Crude Oil is a mixture of a very large number of compounds.
• Most of the compounds in crude oil are hydrocarbons.
  • Hydrocarbons are molecules made of only carbon and hydrogen atoms
• The many different hydrocarbons in crude oil may be seperated into fractions, each of which contains molecules that contain a similar amount of carbon atoms, by evaporating the crude oil and allowing it to condense at a number of different temperatures.
  • This process is called Fractional Disitillation 

Hydrocarbons:

• Most hydrocarbons in crude oil are saturated hydrocarbons called alkanes 
  • The general formula for alkanes is C _nH _2 n+2 
• Alkanes can be represented in two ways
  • CH₄

• Some properties of hydrocarbons depend on the size of their molecules, influencing how they are used as fuels:
  • Boiling point- the boiling point of hydrocarbons increases as the number of carbon atoms in the molecule increases. This is because forces between molecules increase as the size of the molecule increases.
  • Viscosity- the longer the chain of carbons, the more viscous the hydrocarbon is
  • Flammability- the shorter the chain of carbons, the more flammable the hydrocarbon is.

Fuels:

• Elements can burn in the air to form oxides
  • These can be classified as acidic, basic or amphoteric
• When substances burn in air they are reacting with the oxygen
• Oxidation and reduction involve the addition and removal of oxygen respectively
• Most fuels contain carbon and/or hydrogen and may also contain some sulphur.
• The gases released into the atmosphere when a fuel burns may include carbon dioxide, water vapour, carbon monoxide, sulphur…