Chemistry: Developing Fuels

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  • Developing Fuels
    • Petrol
      • Diesel
        • Diesel has a cetane number of C100
      • Petrol
        • Petrol has an octane number of C5 - C7
        • Octane number is the tendency of a petrol based fuel to auto ignite. the higher the octane number the less likely it is to auto ignite
      • Properties
        • Flammability - how easily it is ignited
          • Knocking: happens if a fuel auto ignites in the engine and also ignited by a spark
        • Viscosity - flow from tank to car
          • In the winter petrol has to be viscous
        • Volatility - needs a balance, has to mix with air but you dont want it to evaporate
          • In the summer petrol has to be less volatile so that it doesnt evaporate
    • Catalysts
      • Cracking
        • starts with alkanes that have large molecules that are too big to use in petrol
          • larger molecules are broken down to give alkanes with shorter chains that can be used in petrol
        • Increases the octane number of petrol
        • Zeolite catalyst
      • Isomerisation
        • Takes straight chain alkanes and heats them in a catalyst so that the chains break and then let the fragments join together again
        • When fragments join up they are more likely to do so as branch
        • Aluminium oxide catalalyst
        • Seperation of the isomers
          • Molecular sieves made from zeolite
            • Straight chains pass through the sieve and the branched chains are caught
            • Straight chain alkanes are then recycled over the platinum catalyst
        • Increase the octane number of petrol
      • Reforming
        • Straight chain alkanes are converted into ring compounds
        • first to cycloalkanes and then to aromatic hydrocarbons
        • Increase the octane quality of petrol components
    • Enthalpy
      • Standard enthalpy change of combustion
        • the enthalpy change when one mole of a substance is completely burned in oxygen under standard conditions
        • Example: CH4 + 2 02 ? CO2 + 2 H2O
      • Standard enthalpy change of formation
        • the enthalpy change when one mole of a compound is formed from its elements under standard conditions
        • Example: H2O ? H2 _ 0.5 O2
      • Standard enthalpy change of reaction
        • the enthalpy change when molar quantities of reactants react together under standard conditions
      • The enthalpy change gives the quantity of energy transferred to or from the surounding during a chemical change
        • Positive enthalpy is ENDOTHERMIC
        • Negative enthalpy is EXOTHERMIC
        • How to work out the enthalpy: 1) divide joules by 1000 2) Work out moles 3) divide by number of moles
        • Breaking bonds requires energy
        • Making bonds gives out energy
        • Bond enthalpies are not exact they are an average of many compounds
    • Entropy
    • Alkanes
      • Cycloalkanes
      • Alkenes
      • Straight-chain
      • Branched chain
      • Alcohols
    • Hess cycle
      • Hess Law: the enthalpy change for any chemical reaction is independent of the intermediate stages so long as the initial and final conditions are the same for each route
    • Pollutants
    • Volume of gases
  • The enthalpy change gives the quantity of energy transferred to or from the surounding during a chemical change
    • Positive enthalpy is ENDOTHERMIC
    • Negative enthalpy is EXOTHERMIC
    • How to work out the enthalpy: 1) divide joules by 1000 2) Work out moles 3) divide by number of moles
    • Breaking bonds requires energy
    • Making bonds gives out energy
    • Bond enthalpies are not exact they are an average of many compounds

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