Doc Brown's Chemistry Revision

Oil, its many useful products, environmental problems and an introduction to organic chemistry

1. Fossil Fuels

Revising for KS4 Science GCSE/IGCSE/O level Chemistry Revision-Information Study Notes for revising for AQA GCSE Science, Edexcel 360Science/IGCSE Chemistry & OCR 21stC Science, OCR Gateway Science  (and courses equal to US grades 9-10)

Index of KS4 Science GCSE/IGCSE Chemistry Oil & Organic Chemistry Pages: 1. Fossil Fuels : 2. Fractional distillation of crude oil & uses of fractions : 3. ALKANES - saturated hydrocarbons and combustion : 4. Pollution, carbon monoxide, nitrogen oxides, what makes a good fuel?, climate change-global warming : 5. Alkenes - unsaturated hydrocarbons : 6. Cracking - a problem of supply and demand, other products : 7. Polymers, plastics, uses and problems : 8. Introduction to Organic Chemistry - Why so many series of organic compounds? : 9. Alcohols - Ethanol - properties and reactions : 10. Carboxylic acids and esters : 11. Addition polymers and condensation polymers : 12. Natural Molecules - carbohydrates - sugars - starch : 13. Amino acids, proteins, enzymes & chromatography : 14. Oils, fats, margarine and soaps : 15. Vitamins, drugs-analgesic medicines & food additives : 16. Ozone, CFC's and free radicals : Extra notes, ideas and links on Global Warming and Climate Change : Multiple Choice Quizzes: Oil Products (GCSE easier-foundation-level) : Oil Products (GCSE harder-higher-level) : GCSE Aspects of Organic Chemistry and 3 Easy GCSE Oil Products word-fill worksheets : EMAIL query?comment

1. The origin of oil and other fossil fuels - what are they formed from?

FIRST - a warning! Most of the chemistry described on this page, as well as most developed national economies, is based on crude oil at the moment, and, will no doubt to continue to do so for some time - but NOT FOREVER. Unfortunately oil won't last forever and much of our 'oil based economy' is not sustainable in the future and the potential dangers to the planet from 'climate change' i.e. the global warming from the 'Greenhouse Effect' aided by fossil fuel burning also make uncomfortable thinking. As the world population increases, oil based agriculture is not going to be able to feed everyone. Food production uses huge amounts of energy in the production of artificial-synthetic fertilisers, transportation and machinery on farms. Therefore, one would hope that more 'green sustainable' economic systems will be developed including alternative energy supplies not based on fossil fuels and major changes in agricultural practices to be much less reliant on 'oil' and 'greener' methodology in the chemical industry itself. It is fair to point out that crude oil is an extremely valuable chemical raw material and produces really useful products from smart material plastics to lifesaving drugs and components in many consumer products that are genuinely useful to improving the quality of our lives. therefore burning it is its crudest possible use. In the long-run it should be conserved and used much more sparingly for specific and necessary purposes.

 (April 4th 2009 - xref OilProducts/ExtraOrganic/4_73NH3)

• Crude oil is formed from organic material of the remains of plant and animal organisms that lived millions of years ago.  These remains form sediments e.g. at the bottom of seas, and  become buried under layers of sedimentary rock. They  decay, without air (oxygen), under the action of heat and pressure to form crude oil over millions of years.

  • The vast majority of compounds found in crude oil are hydrocarbons, that is compounds/molecules made up of carbon atoms combined with hydrogen atoms.

• It is a fossil fuel because it is formed from once living organisms and the Sun is the original source of energy. It is a non-renewable and finite (limited reserves) energy resource because it takes millions of years to form and we burn it faster than its is formed! It is also known as a finite energy resource because it will eventually run out! We do not have unlimited oil reserves!

• Coal, peat and natural gas are the other principal non-renewable fossil fuels formed from the remains of plants or animals.

  • Coal, formed millions of years from the remains of tropical plant material, mainly consists of carbon,  Burning coal produces a lot of pollution as the greenhouse gas carbon dioxide. The pollutants include soot particles (black deposits of carbon), sulphur dioxide (lung irritant and acid rain gas) and poly-aromatic hydrocarbons which are carcinogenic.

    • The main reaction on burning is ...

    • carbon + oxygen ==> carbon dioxide

    • C_(s) + O_2(g) ==> CO_2(g)

  • Natural gas, mainly the hydrocarbon methane CH₄, is often found with oil. It consists of 25% by mass of hydrogen and 75% carbon, and, apart from the 'greenhouse' CO₂, produces far less pollution than coal on combustion.

    • The main reaction on burning is ...

    • methane + oxygen ===> water + carbon dioxide

    • CH_4(g) + 2O_2(g) ==> CO_2(g) + 2H₂O_(l)

  • Peat ('turf') is formed over hundreds-thousands of years from the decay of plant material in the absence of oxygen, in boggy-water logged ground. It is a poor quality fuel since the carbon content is much less than in coal and large amount of ash formed on combustion. However, there is a peat fired power station in Ireland.

• THE CARBON CYCLE: When the fossil fuels are burned the 'carbon', as carbon dioxide, is returned to the atmosphere of the Earth's environment. There, it gets absorbed by plant leaves and used up in photosynthesis with the help of sunlight energy and green chlorophyll. The plant material decays reforming carbon dioxide, or, is eaten by animals and used in respiration to form carbon dioxide. Either way, this completes the carbon cycle. See also evolution of Earth's atmosphere.

  • photosynthesis: carbon dioxide + water ==> glucose + oxygen

    • 6CO₂ + 6H₂O ==> C₆H₁₂O₆ + 6O₂ 

  • respiration: glucose + oxygen ==> carbon dioxide + water

    • C₆H₁₂O₆ + 6O₂  ==> 6CO₂ + 6H₂O

    • and fossil fuel combustion, forest fires etc. all return carbon dioxide to the atmosphere

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