Hydrocarbons 2.5

• Compounds derived from organisms that lived long ago that can be used as a source of energy

  • Fossil fuels
• Combustion of fossil fuels

  Produces CO2 - a greenhouse gas that causes an increase in the Earth's temperature
• Insufficient oxygen during combustion of fossil fuels

  Carbon monoxide, a toxic gas, is formed
• Combustion of fossil fuels

  Produces SO2 and NOx which react with water molecules in the air to produce H2SO4 and HNO3 - acid rain
• SO2 and NOx also cause health problems for people with breathing difficulties
• Alkanes


  Saturated hydrocarbons with the general formula CnH2n+2, generally unreactive since they are non-polar and only contain sigma (σ-) covalent bonds
• Combustion of alkanes


  1. Alkanes burn in excess oxygen to produce carbon dioxide and water

  2. If insufficient oxygen is present, carbon monoxide or even carbon will form
• Halogenation of alkanes


  1. Alkanes react with chlorine in UV light to form a halogenoalkane

  2. Mechanism has three stages: initiation, propagation, termination
• Alkenes


  Unsaturated hydrocarbons with the general formula CnH2n, have at least one C=C double bond made up of a sigma (σ-) bond and a pi (π-) bond
• Hydrogenation of alkenes


  Ethene reacts with hydrogen and a nickel catalyst at 150°C to produce ethane
• Electrophilic addition of halogens to alkenes

  1. Halogens react with alkenes to form dihalogenoalkanes

  2. Mechanism involves the use of 'curly arrows' to show the movement of a pair of electrons
• Addition of hydrogen halides to alkenes

  Symmetrical alkenes produce one product, unsymmetrical alkenes produce a major and minor product
• Addition polymerisation


  The double bonds in alkenes and substituted alkenes (monomers) can open up and join together to form long chains called polymers
• 1. Z isomerism


  Example of stereoisomerism, where compounds have the same structural formula but a different arrangement in space due to the inability of the groups attached to the double-bonded carbon atoms to rotate