Developing fuels

• What is a stereoisomer?

  two compounds with the same structural formula but a different arrangement of atoms in space.

  e.g. E/Z isomers
• Why are there two different types of pent-2-ene (E/Z isomerism) ?

  -the c=c bond and atoms bonded directly to it are flat (planar)

  -the shape of the C=CH2 is trigonal planar with an angle of 120degrees

  -atoms can't ROTATE around the c=c bond because its rigid

  -this gives E/Z isomerism
• E isomers


  opposite

  think: Epart (apart)

  
• Z isomers


  together

  think: Zame (same)

  
• electrophile addition


  remember curly arrows, carbocation, electrophile, little delta plus, polarised

  
• when bromine water is added an alkene will...


  ... turn from brown/orange to colourless

  
• alkenes react with hydrogen halides to form...

  haloalkanes

  
• what are addition polymers?

  polymers made from lots of monomers joined together

  common question: what kind of polymer is this? (addition polymer)
• synthetic polymer


  poly(ethene) and poly(propene)
• poly(alkanes)


  -saturated molecules

  -non-polar

  -unreactive

  -don't degrade well in landfill
• alkanes burn completely in oxygen to make...


  only carbon dioxide and water
• alkanes as a fuel

  -they are good fuels because they produce lots of energy. shorter alkanes are more in demand for fuel.

  -burn completely in oxygen

  -power vehicles

  -most of the UK's electricity comes from their combustion
• explain the greenhouse effect

  -EM radiation from sun absorbed by land and sea and some re-emitted as infrared

  -greenhouse gases absorb this radiation and re-emit it back towards earth
• what is incomplete combustion?

  when alkanes burn with limited oxygen supply.

  They make carbon dioxide and soot
• Why is carbon monoxide harmful?

  It's poisonous
• what contributes to photochemical smog?

  unburnt hydrocarbons and oxides of nitrogen when they react in presence of sunlight as they form tropospheric ozone which is a component of photochemical smog, causing respiratory problems and eye irritation.

  - it harms the respiratory system
• what is the ozone?

  -it occurs in the troposphere (the lowest level of the atmosphere)

  -hydrocarbons and nitrogen dioxide (from factories) and sunlight all contribute to the ozone

  -it's toxic
• acid rain


  -fuel burnt contains sulphur impurities, produces SO2 which is acidic and makes sulfuric acid -> acid rain

  -oxides of nitrogen dissolve and make nitric acid -> acid rain
• +/- of fossil fuels

  -non-renewable

  -burning fossil fuels causes greenhouse gases and air pollutants

  -in short supply

  +high energy density

  +relatively easy to extract
• catalytic converters


  -found in vehicles

  -reduce harmful pollutants

  -convert harmful gases into less harmful products
• write an equation to show how carbon monoxide is removed from the exhaust of an engine by a catalytic converter

  2CO + O2 → CO2
• write an equation to show how hydrocarbons are removed from the exhaust of an engine by a catalytic converter

  CxHy + O2 → CO2 + H2O
• write an equation to show how nitrogen oxide is removed from the exhaust of an engine by a catalytic converter


  2NO → N2 + O2
• biofuels


  made from biological matter,

  +renewable

  +carbon neutral

  +when burnt produce less particulates, less CO and no SO2 (compared to fossil fuel)

  -expensive to convert

  -land used

  -burning them produces more NOx than fossil fuels so there will be more tropospheric ozone

  -engines need to be modified
• hydrogen fuel


  can be made by electrolysis of sea water

  +only product is water

  +sustainable if fuel used to extract it is renewable

  +high energy density

  -difficult to store

  -flammable

  -expensive to update infrastructure

  -NOx are produced if hydrogen is produced at high temperatures
• what is molar gas volume?

  -24dm^3 mol^-1

  -the volume occupied by 1 mole of gas under standard conditions.

  -moles= volume(dm^3)/ molar gas volume
• the ideal gas equation

  pV=nRT

  where:

  -p is pressure in pascals (Pa)

  -V is volume in METRES CUBED (m^3)

  -n is the number of moles

  -R is the gas constant, 8.31 kJ^-1 mol^-1 (on data sheet)

  -T is temperature in kelvin (K). 0degreesC is 273 kelvin
• how do you convert from cm^3 to dm^3?

  /1000
• how to use gas equation

  1. write a balanced equation

  2. work out number of moles

  3. use equation to find molar ratio

  4. use the ideal gas equation to work out the number of moles
• enthalpy change


  =total energy to BREAK bonds - total energy released to FORM bonds

  
  

  -written as small triangle then H and a little circle with a line through it.

  -little circle with line through means standard conditions

  -measured in kJ mol^-1

  
• Why do bond enthalpies have positive values?


  to break a bond energy has to be put in/

  breaking bonds is endothermic
• Define the term bond enthalpy.


  energy needed to break 1 mole of bonds

  in the substance in the gaseous state
• Endothermic reaction


  -absorbs energy

  -enthalpy change is POSITIVE

  - bond breaking

  think: ENDothermic -> it's the END of those bonds because they've broken

  
• Exothermic reaction


  -releases energy

  -enthalpy change is NEGATIVE

  -bond making

  
• bond enthalpy


  the amount of energy required to break 1 mole of a bond type of a molecule in the gaseous state
• how to find average bond enthalpy

  -find energy needed to break each bond

  -divide by the number of bonds
• enthalpy change of formation

  The amount of heat evolved or absorbed when 1 mole of a substance is formed from its constituent elements in their standard states under standard conditions.

  
• enthalpy change of combustion

  The amount of heat evolved or absorbed when 1 mole of a substance is burned completely in excess oxygen under standard conditions to make CO2 and H2O.

  
• Hess's Law


  total enthalpy change of reaction is independent of the route taken

  as long as the initial and final conditions remain the same
• energy lost equation


  q=mc∆T

  where

  q=energy lost/ gained in Joules (J)

  m=mass of water or solution

  c= specific heat capacity

  T= temperature change in Kelvin (remember: temp change is the same in degrees C as it is in kelvin)