Developing Fuels - Complete Mindmap

  • Created by: Oliver_C
  • Created on: 20-05-19 16:40
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  • Developing Fuels
    • Enthalpy Change
      • Hess' Law- the total enthalpy change is independent of the route taken
        • H(formation):when 1 mole of a compound is formed from its constituent elements.
        • H(reaction): the enthalpy change when a reaction occurs in the molar quantities shown in the chemical equation
        • H(combustion: enthalpy change when 1 mole of a substance is burnt fully in oxygen.
      • Can be calculated using average bond enthalpies
        • Enthalpy Change of a Reaction is the total energy absorbed to break bonds minus the energy released in making bonds.
        • Why aren't they exact?
          • It's just an average of bond enthalpies from different molecules.
          • The energy needed to break 1 moles of bonds in the gas state, averaged over many different compounds.
      • Bond Enthalpy
        • In covalent molecules the positive nucleus is attracted to the shared electrons.
          • But this means also the nuclei and electrons also repel
            • Bond length is the distance between the nuclei - where the attractive and repulsive forces balance
        • The stronger the attraction between atoms the smaller the bond length and the higher the bond enthalpy
      • Enthalpy Level Diagrams
        • Endothermic
          • Activation energy is big, ?H is positive. Reactants have less energy than the products.
        • Exothermic
          • Reactants has a higher  enthalpy than the products.
      • Calorimetry
        • Burn fuel using spirit burner for ?H  combustion
        • q=mc(delta)T
        • Ideally, all heat given out by the fuel will be absorbed by the water, in practice, however, it's not always the case.
    • Ideal Gas Equation
      • pv=nrT
        • p = pressure in Pa
        • v = volume in m^3
        • n = no. of moles
        • r = 8.314
        • T = temp. in Kelvin (Celius + 273)
        • cm^3 to m^3 divide by 1,000,000
        • dm^3 to m^ divide by 1,000
      • moles = vol/24 at rtp (298 K & 100kPa)
    • Catalysis
      • increases the rate of a reaction by providing an alternate reaction pathway with a lower activation energy
        • catalyst is chemically unchanged at the end
        • e.g. iron in the Haber process
        • e.g. need to be used in cracking to reduce the expenses of high temp./pr.
      • Heterogeneous Catalysts
        • The catalyst is in a different state to the reactants
        • Reactions on heterogeneous catalysts
          • Reactant molecules are adsorbed onto the surface of the catalyst.
            • bonds between the molecule are broken and radicals form
              • these radicals react together to make a new molecule
                • this new molecule is detached from the catalyst surface
        • Poisoning
          • Poison clings more strongly to the surface and so stops the reactant from adsorbing
          • so the catalyst isn't able to be involved in the reaction it's supposed to be speeding up
      • Homogeneous Catalysts are when the catalyst and the reactants are in the same state
    • Organic Groups
      • aromatic compounds (arenes)
        • has a benzene ring
      • aliphatic compounds
        • alcohols
        • alkanes/ alkenes
        • carboxylic acids
        • ketones
        • aldehydes
        • esters
        • ethers
    • Sigma and Pi Bonds
      • Sigma
        • happens when 2 orbitals overlap, in a straight line, between the two atoms
        • This gives maximum electron density between the positive nuclei so sigma bonds are usually very strong
        • single covalent bond
      • Pi
        • weaker than a sigma bond
        • when two p orbitals overlap sideways
        • the two outer parts of a double covalent bond
      • a double bond is made using one pi and one sigma bond
    • Isomerism
      • Structural Isomers
        • Different Carbon Skeleton
          • you can branch straight chained molecules
        • Functional Groups
          • in a different place - e.g. attached to a different carbon
          • same atoms can be arranged into different functional groups
      • Stereoisomer
        • nothing can rotate about the double bond due to the pi bond - they're quite rigid. restricted rotation causes the stereoisomer
        • E/Z Isomers
          • E/Z - E= hydrogens are on different sides. Z= hydrogens are on same side
          • remember only use E/Z when you have 2 hydrogens!
        • same shortened structural formula but different arrangement in space
        • use cis- or trans- when talking about molecules on either ends of a double bond rather than E and Z
    • Addition Reactions of Alkenes
      • Addition Polymerisation
        • monomer into a polymer
        • repeating units should include brackets, line that extend out of the brackets, a single C-C bond and should have an 'n' on the outside
      • Bromine Water to test for C=C bonds
        • orange to colourless due to the electrophilic addition of bromine (or bromination) of the unsaturated molecule.
        • C-C bonds are saturated and thus doesn't react with the bromine
      • Hydrogenation
        • Addition of hydrogen to an unsaturated molecule to make an alkane.
        • nickel catalyst and 150 degrees celcius
      • Electrophilic Addition
        • when the double bond opens up and more atoms can bond with its carbons
        • nucleus is attacked by electrophiles
        • carbocation
        • curly arrow shows the movement of electrons from a place of high electron conc.
      • Reacting with water and sulphuric acid to make an alcohol
        • sulphuric acid is the catalyst
        • you first add the cold sulphuric acid then add water and warm to hydrolyse it.
        • Steam Hydration of Ethene
          • ethene can be hydrated by steam at 300 degrees Celsius and 60 atm of pressure.
            • requires a phosphoric (V) acid catalyst
          • reversible and the initial reaction yield is low
    • Fuels (i.e. "Wishy-washy Chemistry")
      • Carbon Dioxide
        • Produced by most burning of fuels
        • greenhouse gas, which leads to a greater greenhouse effect, hence more global warming
        • generally produced by fossil fuel burning
      • Carbon Monoxide
        • Incomplete combustion of hydrocarbons
        • Poisonous
        • binds to haemoglobin and suffocates you
      • NOx and Unburnt Hydrocarbons
        • reacts with sunlight in the troposphere to form ozone which causes photochemical smog - dangerous for breathing
      • Sulphur Dioxide
        • acid rain
          • can destroy vegetation and limestone builds
      • Particulates
        • can settle in lungs and cause breathing problems
  • Enthalpy change is the heat energy transferred in a reaction at a constant pressure.
    • Reactions can be endo- or exothermic.
      • Exothermic reactions give out energy, so enthalpy change (?H) is negative.
        • E.g. oxidation usually & combustion
      • Endothermic reactions take in more energy than is given out, so ?H is +ive
        • E.g. thermal decomposition and photosynthesis
      • Remember BEN MEX!!
    • Standard Conditions
      • 298 K and 100kPa, or 1atm
      • Elements are in their standard states

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