The Green House effect.

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Introduction

Most of the energy used all over the world comes fro three sources – oil, coal, and natural gas. These are called fossil fuels, because they are made of rotted, semi-fossilized remains of living things from millions of years ago. Today’s fossil fuels where created millions of years ago from plants that photocynthesised using the energy from sunlight which would then remove carbon dioxide from the air thus trapping it as chemical energy. After being squashed under highly immense pressure over the course of millions of years they formed into crude oil. We as a planet are using fossil fuels millions of times faster than they can be formed. A the present rate of use reserves of oil will run out in 100-200 years time and coal in 300-400 years. A biofuel is a gas, liquid or solid that is rendered from

raw biological material such as plants, sewage, dry waste, wood pulp etc, through combustion or fermentation. The difference between fossil fuels and biofuels is that a biofuel is any solid, liquid or gaseous fuel produced from organic (once living) matter, either directly from plants or indirectly from industrial wastes. Whereas a fossil fuel is a fuel such as coal, oil or natural gas formed from the fossilized remains of plants that lived hundreds of millions of years ago. Fossil fuels are a non-renewable energy resource and will eventually run out.

Fossil Fuels contain the products of photosynthesis of plants from millions of years ago but have lost much of their oxygen and are found as hydrocarbons.

The Green House effect.

Today scientists are concerned about global warming. The Earth and its atmosphere act like a green house – light from the sun hits the planet and changes into heat. The atmosphere surrounding the earth acts very much similar to the glass surrounding a green house with light passing through the atmosphere but not being able to leave as with a greenhouse. This causes our planet to slowly get warmer as the heat builds up. The constant burning of fossil fuels are producing gases such as carbon dioxide and cause excessive global warming.

Suitability of fuels.

Heat of combustion

The heat of combustion is the overall energy that is given off when a fuel is burned. We measure this in Kilojoules per mol. When a fuel is burnt an energy source such as a flame would be needed to break the high-energy bonds that are located within the fuel. The two products of combustion are carbon dioxide and water both of which have low energy bonds. The rest of the energy is released as light.

Size of carbon chain-

The smaller fuels require less oxygen to burn completely. For example Methane only needs 2 oxygen molecules to burn completely, where as paraffin needs 21 1/2

Oxygen molecules.  

If oxygen is in short supply then larger fuels such as paraffin will not be able to burn completely.  

This will produce carbon monoxide (a

poisonous gas) or carbon (soot) as well as less energy.

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Flash point

The temperature at which the fuel must be heated in order to produce a mixture that will ignite when exposed to a spark or a flame discovers the flash point of a fuel. The smaller the fuel molecule, the easier it is to ignite.  

Fuel        Flashpoint

Petrol          -45 0F

Diesel         165 0F

Natural gas   -300 0F

Propane      -100-1500F

Biodiesel     -

Ethanol       55

Hydrogen    -

Methanol     52

How much ...

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