Forming Fossil Fuels: CoalForming fossil fuels requires very specific conditions and the conditions are different for each fuel type. One necessary condition the fuels share is the need for an anaerobic environment in which to form.
Those sugar molecules are rings of five or six carbon atoms, and these rings are joined together to make strands. This is the source of the fibres we see in plants. The plant has to construct these rings and fibres. The sugar molecules are produced in a process called photosynthesis, where carbon dioxide, water and sunlight are combined to make sugar molecules. These sugar molecules therefore are a form of stored energy that the plant can use either as energy or as a building material in order to grow larger. This is a brief summary of the process:
When oxygen reacts with the sugars when the plant rots, the rings are broken and the stored energy is lost. The Anaerobic environment.Now we can see that if we remove oxygen from the picture, the rings of stored energy that make up the plant will not be broken down. In short, we need an anaerobic environment, one where there is no oxygen.
For this reason, a swampy, heavily vegetated environment is ideal for forming coal. Trees and other plant matter fall into pools and are quickly covered by mud. This mud prevents air and fresh water from attacking the chemical structure of the sugar chains. During the period of 360 - 300 million years ago environments such as this were widespread and much of the coal we are using today was formed then. That period in history is called the Carboniferous period for this very reason.Over time the plant matter is compressed as more and more mud is deposited on top of it. The weight of all this extra mud eventually squeezes the water, sap and other liquids out of the plant matter, leaving just the sugar chains squashed together. Environments on earth are constantly changing. When the wet swamp eventually changes into a different environment, like a grassland, the old plant matter is now well buried. It can no longer be reached by the oxygen in the air. With more time and more compression, this plant matter goes through a series of transformations. Forming Fossil Fuels: PEAT:
Peat is usually cut from shallow open pits. In many cases it is still moist and needs to be dried before it can be used as a fuel, and the less compressed it has been the more water it will contain.
Brown coal is also turned into commercial fuel briquettes through a process of drying and compressing. We usually see these briquettes in the Weber style barbequeue.
Naturally, Anthracite is even rarer than black coal. The USA, Canada and Peru have major mineable reserves of Anthracite.
Graphite is not generally used as a fuel as it is very difficult to ignite since it has a high activation energy. Instead it is used as an industrial lubricant and also a major component in pencil leads.
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Coal is formed from plant matter. When a tree, for example, dies it begins to rot. The molecules of sugar that the plant has used to build itself are attached by oxygen from the air and broken down. This environment that the tree is decaying in is called an aerobic environment. All this means is that oxygen is available.
First the plant matter becomes peat, a low value fuel that is generally only used these days when no other fuel source is available. This ranges from little more than compressed plant matter to a semi stone like substance that is still very obviously vegetative in origin.
After much more time and compression the peat turns into what is called lignite, commonly known as brown coal. This is a drier fuel and is considerably higher in energy than the peat from which it formed. Still, brown coal can contain up to 70% moisture. The Australian State of Victoria is powered almost exclusively on brown coal, much of which is both mined and burned in power stations in the Latrobe Valley.
Further compression and aging of the brown coal results in black coal, a denser and drier fuel than brown coal. Black coal, also called bituminous coal, is valued as a household fuel source and is also used to manufacture coke for the steel industry. It is however a far rarer resource than brown coal. While 48% of Victoria's energy is supplied from brown coal, black coal does not contribute to the state's power supply in any meaningful way (Australian energy: National and state projections to 2019–2020: Victorian Government).
After more compression and some extreme heating black coal can form into Anthracite, a glossy almost metallic looking substance. This is a very high value fuel source and its primary use is in home and other heating. This substance is a far purer source of bonded carbon than the other types of coal. This means that it comprises mostly of carbon atoms bonded to other carbon atoms, not to elements such as hydrogen. The carbon-carbon bonds are higher energy than the carbon-hydrogen bonds. As this fuel source is richer in carbon-carbon bonds it is an even better fuel than black coal.
Graphite is the final stage of this forming fossil fuels process of compression and heating. All impurities are driven off leaving hexagonal rings of carbon bonded to each other in two dimensional sheets. This type of bonding is incomplete and results in one free electron per carbon atom. These free electrons form "seas" between the sheets of carbon atoms, allowing graphite to conduct electricity. These electrons also give graphite its shine and slippery feel.