AQA CHEMISTRY

• What is a Alkane ?

  A saturated hydrocarbon made up of carbon and hydrogen atoms only
• Why do longer Alkanes have higher boiling points ?

  They have a larger surface area and more electrons

  So there will be more Van der Waals forces
• Why do branched Alkanes have lower boiling points ?

  They have a smaller surface area and cannot pack as tightly together

  So there will be weaker Van der Waals forces
• What is a Saturated hydrocarbon ?

  A hydrocarbon that only contains single bonds between the carbon atoms
• What is a Unsaturated hydrocarbon ?

  A hydrocarbon that contains at least one double bond between the carbon atoms
• What is Crude oil ?

  A mixture of hydrocarbon chains of different lengths
• What is Fractional distillation ?

  When a mixture of hydrocarbons is separated into fractions with similar boiling points
• Describe the process of Fractional distillation

  The crude oil is vaporised

  
  

  The vapour is passed into a fractioning column which is hot at the bottom and cooler at the top

  
  

  The longer chain hydrocarbons will condense and be collected near the bottom of the column

  
  

  The shorter chain hydrocarbons will condense and be collected near the top of the column as they have lower boiling points
• What is the order of collection of Fractional distillation ?

  (top to bottom)

  Fuel gases - LPG

  Gasoline - Petrol in cars

  Naphtha - Petrochemicals

  Kerosene - Jet fuel

  Diesel - Diesel in cars

  Residue - Bitumen/tar
• Why are longer chain hydrocarbons spilt up into smaller ones by cracking ?

  Shorter hydrocarbons are in higher demand
• The products are cracking are ...

  More valuable and useful than the starting products
• What are the conditions for Thermal cracking ?

  High Temperature 900 °C

  High Pressure 70atm

  No catalyst
• What are the products of Thermal cracking ?

  Alkenes
• What are the conditions for Catalytic cracking ?

  High Temperature 400 °C

  Low Pressure 1-2atm

  Zeolite catalyst
• What are the products of Catalytic cracking ?

  Cyclic Alkanes

  Branched Alkanes

  Aromatics
• How do you test for Alkenes ?

  Add Bromine water

  If present change from orange to colourless
• What is produced in the complete combustion of Alkanes ?

  Heat, Carbon dioxide and Water
• What is produced in the incomplete combustion of Alkanes

  Heat, Carbon monoxide and Water

  Or

  Heat, Carbon and Water
• How are Nitrogen oxides produced ?

  When there is energy energy in the air for Nitrogen and Oxygen to react (high temperature)

  
  

  N2 + O2 > 2NO
• How is Sulfur dioxide produced ?

  Combustion of Sulfur

  
  

  It is dangerous because it forms acid rain which can be harmful to the environment
• Why are Carbon particulates and unburnt hydrocarbons a pollutant ?

  They form Smog in the atmosphere

  
  

  This can cause global dimming and respiratory issues
• What is flue gas desulfurisation ?

  The process used by power stations to remove

  SO2 from waste gases.

  It reacts SO2 with Calcium oxide or Calcium carbonate

  
  

  CaO + SO2 > CaSO3

  2CaSO3 + O2 > 2CaSO4 (gypsum)
• What do catalytic converters do ?

  React pollutants together to make less harmful products

  
  

  2CO + 2NO > N2 + 2CO2
• What are catalytic converters made out of ?

  
  

  Why are they honeycomb shaped ?

  Platinum or Rhodium metals

  
  

  To provide a large surface area and so little of the expensive metal is required
• How is global warming caused ?

  Greenhouse gases absorb IR radiation from the sun which causes them to heat up and their bonds vibrate
• What does a molecule have to have to be considered a greenhouse gas ?

  Polar bonds
• What is the name of the process where alkanes react with halogens under UV light to form haloalkanes ?

  Free radical substitution
• What are the 3 stages of Free radical substitution ?

  Initiation, Propagation and Termination
• What happens in Initiation ?

  UV light breaks the bond between 2 chlorine atoms to form 2 chlorine free radicals

  
  

  Cl2 > 2Cl•
• What happens in Propagation ?

  1 radical and 1 non-radical react :

  Cl• + CH4 > CH3• + HCl

  CH3• + Cl2 > CH3Cl + Cl•
• What happens in Termination ?

  2 radicals react to form a non-radical :

  2Cl• > Cl2

  2CH3• > C2H6

  Cl• + CH3• > CH3Cl
• What are Chlorofluorocarbons (CFC's) ?

  Haloalkanes that contain no hydrogen atoms
• How do CFC's deplete the ozone layer ?

  CFC's are broken down by UV light to form Chlorine free radicals which react with ozone

  
  

  Cl• + O3 > ClO• + O2

  ClO• + O3 > Cl• + 2O2
• What is the overall equation for the breakdown of Ozone to Oxygen ?

  2O3 > 3O2
• Why does Chlorine act as a catalyst for the breakdown of the Ozone layer ?

  No Chlorine radicals are lost in the process