Crude oil and organic chemistry

• Energy changes

  Explained by examining the changes in chemical bonding during a reaction
• Energy changes

  Used to classify reactions as exothermic or endothermic
• Exothermic reactions


  • Combustion
  • Neutralisation
  • Oxidation
• Uses of exothermic reactions


  • Self-heating food cans
  • Outdoor hand warmers
• Endothermic reaction

  Energy is taken in from the surroundings
• Endothermic reaction


  Temperature of the surroundings decreases
• Endothermic reactions


  • Thermal decomposition
  • Electrolysis
• Uses of endothermic reactions


  • Instant ice packs used to treat injuries
• Energy level diagram


  Shows whether a reaction is exothermic or endothermic
• Exothermic reactions


  • Products are at a lower energy level than the reactants
  • Energy is given out to the surroundings
  • Downwards arrow shows energy is given out
• Endothermic reactions


  • Products are at a higher energy level than the reactants
  • Energy is taken in from the surroundings
  • Upwards arrow shows energy is taken in
• Reaction profile


  Shows how the energy of the chemicals changes during a reaction
• Activation energy


  Minimum energy needed to start a reaction
• Activation energy


  • Starts at the energy of the reactants
  • Equal to the difference in energy between the top of the 'hump' and the reactant
• Overall change in energy


  Difference between the energy of the reactants and the energy of the products
• Exothermic reactions


  • More energy is released when new bonds are made than is needed to break existing bonds
  • Overall energy change is negative - energy is given out to the surroundings
• Endothermic reactions


  • More energy is taken in when the existing bonds are broken than is released in making new bonds
  • Overall energy change is positive - energy is taken in from the surroundings
• Bond energy


  Amount of energy needed to break one mole of covalent bonds of a given type
• Example calculation of energy change for hydrogen and chlorine reaction
• Hydrocarbons


  Compounds that contain carbon and hydrogen atoms only
• Hydrocarbon chains


  • Can vary in length
  • Longer chains have higher boiling points
• Crude oil


  Complex mixture of hydrocarbons
• Formation of crude oil


  1. Remains of dead marine animals and plants

  2. Covered by sand and sediments

  3. Pressure and heat caused breakdown into crude oil
• Fractions from fractional distillation of crude oil


  • Refinery gases
  • Petrol
  • Naptha
  • Paraffin (kerosine)
  • Diesel oil (gas oil)
  • Lubricating oil
  • Bitumen
• Fractional distillation


  • Crude oil boiled/vaporised
  • Hydrocarbons condense at different heights in column
  • Lower boiling point compounds collected higher in column
• Hydrocarbon fractions


  Mixtures containing compounds with similar chain lengths and boiling points
• Intermolecular forces


  • Hold hydrocarbon molecules together
  • Larger molecules have more forces, needing more energy to overcome for melting/boiling
• Combustion of hydrocarbons


  • Requires oxygen
  • Produces carbon dioxide and water
  • Exothermic - releases heat
• Hydrogen as a fuel


  • Renewable
  • Only produces water as a product
  • Ignites easily
  • Forms explosive mixture with air
• Fire triangle


  Factors required for combustion: fuel, oxygen, heat
• Alkanes


  Contain single bonds between carbon atoms, saturated
• Alkenes


  Contain double bonds between carbon atoms, unsaturated
• Isomers


  Molecules with same molecular formula but different structures
• Hydrogenation of alkenes


  1. Hydrogen added across C=C bond

  2. Forms corresponding alkane
• Bromine water test for alkenes


  Turns from orange/brown to colourless when added to an alkene
• Cracking hydrocarbons


  • Breaking large hydrocarbons into smaller ones by heating and catalysis
  • Produces alkenes
• Monomers


  Small, reactive molecules that can be joined to make polymers
• Polymerisation


  One bond in monomer breaks to allow joining to another monomer
• Examples of polymers

  • Polyethene
  • Polypropene
  • PVC
  • PTFE
• Crude oil


  A mixture of hydrocarbons formed from the remains of simple marine organisms over millions of years