Fuels and Earth Science

• What are hydrocarbons?


  Compounds that contain hydrogen and carbon atoms only
• What is crude oil?


  • A complex mixture of hydrocarbons
  • Contains molecules with rings or chains of carbon atoms
  • An important source of useful substances like fuels and feedstocks for the petrochemical industry
  • A finite resource
• Where can crude oil be found?


  Under the sea and ground
• Crude oil is finite meaning it will run out
• How can crude oil be seperated?


  Fractional distillation
• How does fractional distillation work to separate crude oil?


  • Crude oil is vaporised before it enters a fractioning column
  • fractioning column is hotter at the bottom than at the top. The vapours rise up and condense at different fractions depending on their boiling points.
  • Hydrocarbons with low boiling points will be tapped off the top of the column and hydrocarbons with high boiling points will be tapped off at the bottom of the column
• Why is crude oil separated?


  Unseparated crude oil isn’t very useful but the separated products (such as petrol) are very useful
• Refinery gas is a fraction of crude oil and is normally used in heating and cooking
• Petrol and diesel are also fractions of crude oil used in cars
• Kerosene is a fraction of crude oil and is usually used in aircraft fuel
• Diesel oil is a fraction of crude oil and is usually used as fuel for some cars or trains
• Bitumen is a fraction of crude oil and is used for road surfacing and roofs
• Fuel oil is a fraction of crude oil and is commonly used as fuel for large ships and in some power stations
• How do the hydrocarbons at each faction differ?


  • Boiling points
  • Ease of ignition
  • Viscosity
  • Number of hydrogen and carbon atoms their molecules have
• Where in the fractioning column do hydrocarbons with the highest viscosity condense?


  • Viscosity is how thick and sticky a substance is
  • hydrocarbons with the hugest viscosity ( like bitumen ) are collected at the bottom of the fractioning column
• What are the properties of hydrocarbons that are tapped from the top of the fractioning column ( eg petrol and refinery gas )?


  • Low boiling points
  • highly volatile
  • easily ignited
  • shorter carbon chains (small molecules)
• What is a homologous series?


  Series of compounds which

  • have the same general formula
  • have similar chemical properties
  • differ by CH2 in molecular formula form neighbouring molecules
  • slight variation in physical properties
• Products from crude oil mostly belong to the alkane homologous series
• When a hydrocarbon undergoes complete combustion, what are the only products formed?


  Water (H2O) and Carbon dioxide (CO2)
• When a fuel undergoes complete combustion it is a exothermic reaction
• When does incomplete combustion occur and what is required to ensure complete combustion occurs?


  Incomplete combustion occurs

  when there is an insufficient supply of oxygen.

  • To ensure complete combustion occurs, the reception should be carried out with excess oxygen
• What are the products of incomplete combustion?


  • Carbon particulates - soot (C)
  • Carbon monoxide (CO)
  • Water (H2O)
• What are the problems with carbon monoxide?


  • It is a toxic gas.
  • It is colourless and odourless and if breathed in can cause death by preventing the red blood cells from carrying oxygen around the body
• What are the problems with incomplete combustion?


  • Produces carbon monoxide which is toxic and can be fatal if breathed in
  • Produces carbon particulates known as soot which causes global dimming and respiratory problems
• Some hydrocarbon fuels contain sulfur impurities. When the fuel is burned, the sulfur reacts with oxygen to form sulfur dioxide.
• How is acid rain produced?


  Sulfur dioxide (produced when combusting impure hydrocarbon fuels) evaporates into the air.It reacts with water in the clouds to form sulfuric acid. This is ‘acid rain’
• What problems can acid rain cause?


  • Corrodes buildings and statues made of limestone
  • Kills/damages vegetation
  • Lowers the pH of large bodies of water, killing the wildlife.
• How are oxides of nitrogen produced from car engines?


  The high temperature and pressure of a car engine causes nitrogen and oxygen from the air to react together.
• What problems are associated with oxides of nitrogen?


  • Pollutants
  • Produce acid rain with similar effects as SO2
  • Cause respiratory problems
• What are advantages of using hydrogen as a fuel in cars?


  • It releases more energy per kg compared to most other fuels
  • Water is the only product so no pollutants
  • Renewable source as hydrogen can be extracted from water
• What are the disadvantages of using hydrogen as fuel in cars?


  • It is expensive to produce and a lot of energy is required for the electrolysis of the water to acquire the hydrogen
  • difficult and dangerous to store hydrogen because it is very volatile and easily ignites.
• Non renewable fossil fuel found in natural gas is methane.
• Petrol, kerosene and diesel are non-renewable fuels that are not being readily replaced
• What is cracking?


  • Breaking down large hydrocarbons into smaller more useful ones.
  • Saturated alkanes are cracked into shorter chain alkanes and short chain unsaturated alkenes
• What do the terms saturated and unsaturated mean?


  Saturated means it only contains single bonds.

  Unsaturated means it contains some (C=C) double bonds
• What type of reaction is cracking?


  Thermal decomposition
• Why is cracking necessary?


  The demand for shorter chain alkenes and alkanes is much greater than the demand for long chain alkanes.
• What produced the gases that formed Earths early atmosphere?


  Volcanic activity
• describe how earths early atmosphere formed?


  • Initially earths surface was molten with no atmosphere
  • cooling caused land masses to solidify
  • volcanoes formed on land masses and released gases which formed the early atmosphere
• What was the earths early atmosphere thought to contain?


  • carbon dioxide ( large amounts )
  • methane
  • ammonia
  • water vapour