Developing fuels

• shorter bond = stronger bond
• pV = nRT
• pV = mRT/Mr
• bond making = exothermic

  bond breaking = endothermic
• single bond is called sigma bond

  overlap of orbitals is directly between the two atoms and there is free rotation around the sigma bond
• alkenes

  • unsaturated hydrocarbons (CnH2n)
  • C=C is an area of high electron density making it susceptible to attack from electrophiles
  • alkenes more reactive than alkanes
• bromine water to identify a double bond (orange-brown -> colourless)
• catalyst poisoned by a chemical binding to surface (strong adsorption)
• catalyst poisons

  • sulphur
  • lead
• catalysts

  lower the activation energy by providing an alternative reaction route
• heterogeneous catalysis

  catalysts in a different state to species in reaction
• heterogeneous catalysis

  reactants adsorbed onto catalyst surface

  reactant bonds weaken lowering Ea

  weakened bonds break

  new bonds form between reactants

  products form on catalyst surface

  desorption of products from catalyst surface
• catalytic converters

  unburnt hydrocarbons and oxides of nitrogen can be removed from systems using catalytic converters using a rhodium catalyst to convert harmful products to more stable products (CO2 or H2O)
• oxides of N and S can be produced as byproducts of alkane combustion -> resulting in acid rain

  CO can be produced in incomplete combustion of alkanes

  carbon particulates (fragments of unburnt hydrocarbons) can be produced in fuel combustion
• cracking is used to convert long hydrocarbons into shorter more useful ones
• thermal cracking

  • high temperature and pressure
• catalytic cracking

  • produces aromatic compounds
  • lower temperatures
  • normal pressure
  • catalyst used
• standard conditions

  • pressure of 100kPa
  • temperature of 298K
• double bond = one pi bond one sigma bond
• alkenes react with electrophiles and undergo electrophillic addition about the double bond
• electrophiles are electron acceptors ad attract to areas of high electron density (eg: HBr, Br2, H2SO4)
• alkenes undergo addition reactions with water in the prescence of a catalyst to form alcohols
• alkenes undergo addition reactions with hydrogen in the prescence of a catalyst to form alkanes
• addition polymers are produced from alkenes where the double bond is broken to form a repeating unit
• E/Z isomerism

  arises in compounds with one hydrogen atom attached to each atom in a C=C double bond, isomerism occurs because of limited rotation around the C double bond
• functional group : a group of atoms on a carbon chain that gives the molecule its properties
• dashed line represents going into plane of paper/behind plane of paper
• solid line represents bond on the plane of the paper
• solid wedge represents a bond coming out of the plane of the page
• aliphatic - doesnt contain any aromatic rings
• aromatic - contains a benzene ring
• molecular pollutants

  CO2 , CO , NOx , SOx , unburnt hydrocarbons
• saturated hydrocarbon contains only C-C single bonds
• unsaturated hydrocarbon contains a C=C double bond
• experimental techniques to measure volume of gas

  • use a gas syringe
  • measure mass lost on a weighing balance and calculate moles of gas produced
  • collect gas produced in an upturned test tube filled with water
• enthalpy change of reaction : the enthalpy change when quanitities of substance in standard states react completely under standard conditions
• enthalpy change of formation : the enthalpy change when one mole of a substance is produced from its constituent elements under standard conditions
• enthalpy change of combustion : the enthalpy change when one mole of a substance is burned completely in oxygen under standard conditions
• enthalpy change of neutralisation : the enthalpy change when solutions of acid and alkali react together under standard conditions to produce one mole of water
• q = mcΔt