school energy&environment

What is it?

Oil is a fossil fuel, just like coal and natural gas. Such fuels derive from the remains of plants and animals which died hundreds of million years ago, when mankind had not yet appeared on Earth. Those plants and animals, as it happens today, have accumulated the energy coming from the Sun and, after their death, have remained buried for millions of years until they have turned into oil and coal. Prehistoric animals and plants today return the solar energy they accumulated in the past as heat and electric energy. Great part of the energy we use today comes from fossil fuels, especially oil. However, it is a non-renewable energy source which is bound to depletion sooner or later.
More specifically, oil is a natural mixture of liquid hydrocarbons and other substances of fossil origin contained in sedimentary rocks and associated to smaller quantities of gaseous (natural gas) and solid (bitumen) hydrocarbons.
All the molecules of the existing hydrocarbons include two types of atoms only: carbon and hydrogen atoms. According to the quantity of carbon atoms included in the molecule, hydrocarbons can be in gaseous (up to 4 atoms), liquid (from 5 to 16 atoms) or solid state (over 16 atoms). Hydrocarbons make up a wide range of substances, since carbon can easily link to other carbon and hydrogen atoms to form open chains (linear or ramified), closed chains (ring, cyclic hydrocarbons like benzene have only one ring) or mixed chains (with open and ring structures).
There are thousands of hydrocarbons with different molecular structures and the same chemical composition. There are hydrocarbons with single bonds (alkanes or saturated hydrocarbons, such as methane), double bonds (alkenes such as propylene) or triple bonds (alkynes, such as acetylene). By means of a hot treatment in the absence of air (a process called cracking), the bond of heavier hydrocarbons can be broken to obtain lighter and more flexible molecules making up the infinite range of petrochemical products.