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GCSE Chemistry > Carbon Cycle

The carbon cycle is simply the process by which Carbon Dioxide is put into and removed from the atmosphere. This process is very finely balanced to keep the percentage of CO2 in the atmosphere at 0.03%. Even so, man is doing his part to unbalance this cycle by excess burning of fossil fuels and deforestation.

The reactions involved in the carbon cycle are as follows:

  • Combustion - exothermic reactions at a very fast rate

    Fuel [Methane]   +   Oxygen   ---->   Carbon Dioxide   +   Water   (+ energy)
    CH4 (g)   +   2O2 (g)   ---->   CO2 (g)   +   2H2O (l)

  • Evaporation of Sea Water (containing dissolved CO2)

    Carbon Dioxide dissolves in sea water. Some of the water evaporates and CO2 is released. This is a reversible reaction:

    Sea Water   +   Sunlight   <---->   Water   +   Carbon Dioxide
    H2O (l)   +   CO2 (g)   <---->   H2CO3 (aq) [Carbonic Acid]

  • Decay of Organic Matter

    Plants and animals decay to leave behind coal, oil, and gas after millions of years of being squashed by materials above. Some materials just decay and a form of respiration occurs that releases Carbon Dioxide. CO2 is also given off when the raw materials mentioned above decay.

  • Photosynthesis

    Plants make sugar from light using carbon dioxide and water. These constituents are catalysed by chlorophyll in green leaves to form glucose, which the plant requires. The bi-product is Oxygen.

  • Respiration

    Respiration is the name of the process which involves animals ingesting food and inhaling air. The inhaled air dissolves in the blood and is transported around the body. Some of the oxygen is used within cells to oxidise sugars. When this occurs, CO2, H2O, and O2 are released.

    Glucose   +   Oxygen   ---->   Carbon Dioxide   +   Water   +   Energy

  • Sedimentation

    Under extreme pressure, dead sea creatures decay without air deep underground. Over millions of years, the sea creatures become oil, or natural gas. Also, when shells of sea creatures etc... build up in layers over millions of years, sedimentary rock can be formed.

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