Fuels, Alkanes and Alkenes

• Homologous series

  A family of organic compounds with the same functional group and similar chemical properties
• Functional group

  An atom or a group of atoms that gives a molecule its characteristic properties
• Homologous series


  • Alkanes
  • Alkenes
  • Alcohols
  • Carboxylic acids

  
• Homologous series and their functional groups

  • Alkanes: no functional group
  • Alkenes: carbon-carbon double covalent bond
  • Alcohols: hydroxyl group
  • Carboxylic acids: carboxyl group

  
• General characteristics of a homologous series

  • Same functional group
  • Similar chemical properties
  • Different from the next member by –CH2– group
  • Gradual change in physical properties
  • Same general formula
  • Prepared using similar methods
• Prefix


  Shows the number of carbon atoms in each molecule
• Suffix


  Shows the homologous series that the compound belongs to
• Suffixes and their corresponding homologous series

  • –ane: alkane
  • –ene: alkene
  • –ol: alcohol
  • –oic acid: carboxylic acid
• Alkanes


  Saturated hydrocarbons that contain only carbon–carbon single covalent bonds

  
• General molecular formula for alkanes


  CnH2n+2 where n = 1, 2, 3 etc.

  
• Each member of the alkane homologous series differs from the next by a –CH2– unit

  
• Unbranched alkanes


  • Methane: CH4
  • Ethane: C2H6
  • Propane: C3H8

  
• Physical properties of alkanes

  • Low melting and boiling points
  • Insoluble in water
  • Soluble in organic solvents
• Physical properties trends of alkanes

  Melting and boiling points increase down the homologous series
• Alkanes are generally unreactive except in terms of combustion and substitution by chlorine

  
• Combustion of alkanes


  1. Burn in excess air to produce carbon dioxide and water vapour

  2. Complete combustion produces carbon dioxide and water only

  3. Incomplete combustion produces carbon dioxide, carbon monoxide, soot, and water
• Substitution reactions of alkanes

  React with halogens in the presence of UV light

  
• Alkenes


  Unsaturated hydrocarbons that contain one or more carbon–carbon double bonds

  
• General molecular formula for alkenes


  CnH2n where n = 2, 3, 4, etc.

  
• Unbranched alkenes


  • Ethene: C2H4
  • Propene: C3H6

  
• Physical properties of alkenes

  • Low melting and boiling points
  • Insoluble in water
  • Soluble in organic solvents
• Combustion of alkenes


  1. Burn in excess air to produce carbon dioxide and water vapour

  2. Incomplete combustion produces carbon dioxide, carbon monoxide, water vapour, and carbon

  
• Addition reactions of alkenes

  Carbon–carbon double bonds are very reactive and undergo addition reactions readily

  
• Addition reaction: Hydrogenation


  1. Addition of hydrogen to alkenes to form alkanes

  2. Conditions: High temperature, nickel catalyst

  
• Addition reaction: Bromination


  1. Addition of bromine to alkenes to form bromoalkanes

  2. Conditions: Room temperature and pressure

  
• Alkane does not decolourise bromine solution under normal conditions

  
• Alkene decolourises reddish-brown bromine solution

  
• Polyunsaturated fat molecules


  Contain more than one –C=C– bond in their molecules
• Manufacture of margarine


  Reacting unsaturated vegetable oils with hydrogen in the presence of nickel catalyst at high temperature and pressure
• Types of fats


  • Saturated fats: solids at r.t.p.
  • Unsaturated fats: liquids at r.t.p.
• Examples of fats and oils

  • Fats: butter, margarine
  • Oils: vegetable oil, olive oil
• Cracking

  A process in which larger hydrocarbon molecules are broken into smaller hydrocarbon molecules
• How cracking is done

  1. Using a catalyst at high temperature

  2. Conditions: Aluminium oxide and silicon (IV) oxide, high temperature, pressure of 1 atm
• An alkene is always produced in cracking
• Organic Compounds


  All organic compounds contain the element carbon
• Not all carbon-containing compounds are organic
• Non-organic carbon-containing compounds


  • Carbon dioxide
  • Carbon monoxide
  • Metal carbonates
• Hydrocarbons


  Organic compounds that contain only hydrogen and carbon
• Example of a hydrocarbon


  • Crude Oil (Petroleum)
• Crude oil consists mainly of hydrocarbons