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
- But this means also the nuclei and electrons also repel
- The stronger the attraction between atoms the smaller the bond length and the higher the bond enthalpy
- In covalent molecules the positive nucleus is attracted to the shared electrons.
- 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.
- Endothermic
- 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.
- Hess' Law- the total enthalpy change is independent of the route taken
- 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)
- pv=nrT
- 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
- these radicals react together to make a new molecule
- bonds between the molecule are broken and radicals form
- Reactant molecules are adsorbed onto the surface of the catalyst.
- 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
- increases the rate of a reaction by providing an alternate reaction pathway with a lower activation energy
- Organic Groups
- aromatic compounds (arenes)
- has a benzene ring
- aliphatic compounds
- alcohols
- alkanes/ alkenes
- carboxylic acids
- ketones
- aldehydes
- esters
- ethers
- aromatic compounds (arenes)
- 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
- Sigma
- 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
- Different Carbon Skeleton
- 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
- Structural Isomers
- 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
- ethene can be hydrated by steam at 300 degrees Celsius and 60 atm of pressure.
- Addition Polymerisation
- 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
- acid rain
- Particulates
- can settle in lungs and cause breathing problems
- Carbon Dioxide
- Enthalpy Change
- 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!!
- Exothermic reactions give out energy, so enthalpy change (?H) is negative.
- Standard Conditions
- 298 K and 100kPa, or 1atm
- Elements are in their standard states
- Reactions can be endo- or exothermic.
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