Topic 8 - Fuels and Earth Science

• What are hydrocarbons?


  Compounds that only contain carbon and hydrogen atoms
• 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.
• What does it mean when crude oil is described as 'finite' ?

  It will run out
• How can crude oil be separated?

  fractional distillation
• How does the process of fractional distillation work to separate crude oil?

  - Crude oil is vaporised before it enters a fractionating column.

  - The fractionating 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 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. What are its common uses?

  heating and cooking
• What fraction of crude oil is used as fuel in cars?

  Petrol (gasoline).

  Diesel is also less commonly used.
• Kerosene is a fraction of crude oil. What is a common use of kerosene?

  Aircraft fuel
• Diesel oil is fraction of crude oil. What is it commonly used for?

  Fuel for some cars and trains
• Which fraction of crude oil is used for road surfacing and roofs?

  Bitumen
• Fuel oil is a fraction of crude oil. What is it commonly used for?

  Fuel for large ships and some power stations
• How do the hydrocarbons at each fraction differ?

  - Boiling points.

  - Ease of ignition.

  - Viscosity.

  - The number of hydrogen and carbon atoms

  their molecules have.
• Where in the fractionating column do hydrocarbons with the highest viscosity condense?

  Viscosity is how thick and sticky a substance is.

  
  

  The hydrocarbons with the highest viscosity (like bitumen) are collected at the bottom of the fractionating column.
• What are the properties of hydrocarbons that are tapped from the top of the fractionating column, like petrol and refinery gas?

  - Low boiling point.

  - 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 which homologous series?

  Alkane homologous series.
• What are the only products when a hydrocarbon fuel undergoes complete combustion?

  water (H2O)

  carbon dioxide (CO2)
• True or false?

  Energy is given out when a fuel undergoes complete combustion

  True

  The reaction is exothermic.
• Write a balanced symbol equation for the complete combustion of ethane

  2C2H6 + 7O2 → 4CO2 + 6H2O
• When does incomplete combustion occur? 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 reaction should be carried out with excess oxygen.
• What are the products of incomplete combustion?

  Carbon particulates - soot (C).

  Carbon monoxide (CO).

  Water (H2O).
• Write a balanced symbol equation for the incomplete combustion of methane to form carbon monoxide

  2CH4 + 3O2 → 2CO + 4H2O
• Write a balanced symbol equation for the incomplete combustion of methane to form carbon particulates

  CH4 + O2 → C + 2H2O
• What are the problems with carbon monoxide?

  Carbon monoxide 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.

  It bind preferentially to red blood cells over haemoglobin.
• What are the problems with incomplete combustion?

  - Produces carbon monoxide which is toxic and

  can be fatal if breathed in.

  - Produces carbon particulates (soot) which

  cause global dimming and respiratory

  problems.
• Why is sulfur dioxide sometimes produced when burning hydrocarbon fuels?

  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 the 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 the 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 a fuel in cars?

  - It is expensive to produce and a lot of energy is required for the electrolysis of water to acquire the hydrogen.

  - Difficult and dangerous to store hydrogen because it is very volatile and easily ignites.
• Name the non-renewable fossil fuel found in natural gas

  methane
• Are petrol, kerosene and diesel renewable fuels?

  No, they are non-renewable.

  
  

  They are finite resources which 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 - only contains single bonds.

  
  

  Unsaturated - 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.