Fuels and Earth Science

• Fossil fuels like coal, oil and gas are called non-renewable fuels. They are finite resources - so one day they will run out.
• Crude oil is our main source of hydrocarbons and is used as a raw material to create lots of useful substances used in the petrochemical industry.
• Crude oil is a complex mixture of lots of different hydrocarbons - compounds which contain just carbon and hydrogen. The hydrocarbons found in crude oil have their carbon atoms arranged in either chains or rings and are mostly alkanes.
• The different fractions in crude oil are separated by fractional distillation. The oil is heated until most of it has turned into gas. The gases enter a fractionating column - and the liquid bit, bitumen, is drained off at the bottom.
• In the column, there is a temperature gradient, it is hot at the bottom and gets cooler as you go up.

  
• A homologous series is a family of molecules which have the same general formula and share similar chemical properties.
• Hydrocarbons make great fuels because the combustion reactions that happen when you burn them in oxygen give out lots of energy - the reactions are very exothermic.
• When you burn hydrocarbons in plenty of oxygen, the only products are carbon dioxide and water - this is called complete combustion.
• Incomplete combustion occurs when a hydrocarbon burns in a limited supply of oxygen.
• Incomplete combustion produces carbon monoxide - a toxic gas and carbon in the form of soot.
• Carbon Monoxide can combine with red blood cells and stop your blood from doing its proper job of carrying oxygen around the body. A lack of oxygen in the blood supply to the brain can lead to fainting, a coma or even death.
• When fossil fuels are burned, they release mostly C02, but they also release other harmful gases - especially sulfur dioxide and various nitrogen oxides. The sulfur dioxide comes from sulfur impurities in fossil fuels. When sulfur dioxide mixes with clouds, it forms dilute sulfuric acid. This then falls as acid rain.
• Nitrogen oxides are created from a reaction between the nitrogen and oxygen in the air, caused by the energy released by combustion reactions. Nitrogen oxides are harmful pollutants - they can contribute to acid rain and at ground level, can cause photochemical smog (a type of air pollution that can cause breathing difficulties).
• Hydrogen can be used as a clean, renewable fuel:

  Advantages:

  • the only waster product is water
  • it is obtained from water which is a renewable resource so it won’t run out
• Hydrogen can be used as a clean, renewable fuel:

  Advantages:

  • the only waste product is water
  • hydrogen is obtained from water which is a renewable resource so it won’t run out.

  Disadvantages:

  • you need a special, expensive engine
  • hydrogen gas has to manufactured which is expensive and sometimes uses energy from another source
  • it is hard to store.
• Cracking turns long saturated (alkane) molecules into smaller unsaturated (alkene) molecules - which are more useful.
• Cracking is a form of decomposition, which is when one substance breaks down into at least two new ones when you heat it.
• Cracking involves heat, moderate pressures and a catalyst.
• Cracking helps matches the supply and demand because it creates smaller molecules that can be used for everyday things.
• The Atmosphere -> Phase 1

  The Earth’s surface was originally molten for many millions of years. Eventually, the Earth’s surface cooled and a thin crust formed, but volcanoes kept erupting, releasing gases inside the Earth. When things eventually calmed down, the early atmosphere was mostly carbon dioxide and water vapour. The water vapour condensed to form the oceans.

  
• Nitrogen gas was put into the atmosphere in two ways:

  • Formed by ammonia reacting with oxygen
  • Released by denitrifying bacteria
• The Greenhouse Effect helps to keep the Earth warm.

  
• Increasing greenhouse gases causes climate change.
• In order to prevent or slow down climate change, we need to cut down on the amount of greenhouse gases we’re releasing into the atmosphere.
• The Atmosphere -> Phase 2

  A lot of the early carbon dioxide dissolved into the oceans. Nitrogen gas was then put into the atmosphere. Nitrogen gas isn’t very reactive, so the amount of nitrogen gas in the atmosphere increased because it was being made but not broken down. Green plants then evolved and increased the amount of oxygen in the air.

  
• The Atmosphere -> Phase 3

  The build up of oxygen in the atmosphere killed off early organisms. This allowed the evolution of more complex organisms that made use of the oxygen. The oxygen created an ozone layer which blocked harmful rays from the Sun and enabled even more complex organisms to evolve.