Hydrocarbons are molecules that contain only hydrogen and carbon atoms. Smaller hydrocarbons include methane, propane and butane gases. Medium-sized hydrocarbons include liquids such as octane in petrol, and kerosene. Large hydrocarbons are solids such as tar and bitumen.
Crude Oil is a mixture of hydrocarbons when it is drilled out of the ground or seabed.
Fractional Distillationis the process of heating crude oil to higher and higher temperatures, so that different parts or fractions of the hydrocarbon mixture evaporate and are collected one by one. The gases used in LPG (Liquid Petroleum Gas) would be collected first, followed by the liquids such as petrol and kerosene. The remaining hydrocarbons would then be the solid tar and bitumen.
Cracking is a process which follows Fractional Distillation. Two of the liquid forms of hydrocarbons (Naphtha and Kerosene) are further broken or "cracked" by catalysts into smaller hydrocarbons. These smaller hydrocarbons are then used as petrol (iso-octane) or in the manufacture of plastics (ethene).
Types of Hydrocarbons
Alkanes are hydrocarbons that contain only single bonds. Examples include methane CH4 and ethane C2H6. The general formula for alkanes is CnH2n+2.
Alkenes are hydrocarbons that contain at least one double bond. An example is ethene C2H4. The general formula for alkenes is CnH2n.
Alkynes are hydrocarbons that contain at least one triple bond. An example is ethyne C2H2. The general formula for alkynes is CnH2n–2.
NAME OF ALKANE
NUMBER OF CARBON ATOMS
CH3 CH2 CH3
CH3 (CH2)2 CH3
CH3 (CH2)3 CH3
CH3 (CH2)4 CH3
CH3 (CH2)5 CH3
CH3 (CH2)6 CH3
CH3 (CH2)7 CH3
CH3 (CH2)8 CH3
Combustion of Hydrocarbons
All hydrocarbons burn to form water and carbon dioxide.