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# Case Study: Fossil Fuels

Fossil Fuels, oil, natural gas, and coal, are energy resources that formed millions of years ago from plant and animal life. They are our main form of power used to fly airplanes, drive cars, and heat homes. Fossil Fuels alone are estimated to provide around 85% of the worlds total energy demands. Currently, there is much controversy over the carbon emissions that fossil fuels release into the environment when combusted. Many are searching for alternative forms of energy that reduce carbon emissions, are cost effective, and can be easily created. To better understand fossil fuels lets look at: how they are formed, what they are made out of, their uses, benefits, and limitations.

### Introduction

It takes about 250-500 million years for fossil fuels to form. The process takes such a long time because fossil fuels are formed from fossilized remnants of plants and animals deep in the Earth's crust. Heat and pressure, out of contact with air, can transform the decomposed material into little sacks of gas and unrefined oil. The oil and gas then moves through the small holes of space in the rocks to eventually collect in reservoirs. Coal comes mainly from dead plants, much like the other two fossil fuels, which have been buried and compacted below the surface of the Earth.

Picture of how fossil fuels are created

### What are Fossil Fuels made out of?

Oil: Commonly referred to as petroleum, oil is made up of various hydrocarbons. The major classes of hydrocarbons in petroleum are:

• Paraffins- (CnH2n+2) where "n" is a whole number between 1-20. ex. Methane (CH4), ethane (C2H6), and propane (C3H8)
• Aromatics- (C6H5 - Y) where "Y" is a longer, straight molecule that connects to the benzene ring. ex. Benzene (C6H6)
• Napthenes or Cycloalkanes- (CnH2n) where "n" is a whole number between 1-20. ex. Cyclohexane (C6H12)

Natural Gas: Natural gas is comprised mainly of the following carbon-hydrogen compounds:

• Methane (CH4)
• Ethane (C2H6)
• Propane (C3H8)
• Butane (C4H10).

Coal: Coal is comprised of carbon, hydrogen, nitrogen, sulfur, and/or oxygen. The chemical formula for coal depends upon where it is mined but is mainly:

• 90% carbon
• And the remaining elements are Hydrogen (H2), Nitrogen (N2), Sulfur (S), and Oxygen (O2)
• i.e. C10H2

### Fossil Fuels are used to:

Providing Electricity: One of the main uses of fossil fuels is to provide electricity. Of the three fossil fuels, coal is the top fuel source used in creating electricity. Around 100 billion tons of coal is burned yearly to generate electricity in the United States.

For Heating and Cooling: Natural gas and oil are the main fossil fuel contributors when it comes to heating and cooling. To create a comfortable climate in your home these two fossil fuels are burnt, therefore releasing energy, and powering up your air conditioner or stove.

For Fueling Transportation: Oil is primarily responsible for fueling our automobiles, airplanes, buses, trucks, and boats. It is mainly used in the form of gasoline and diesel to power such vehicles. It is has been estimated that about 98 tons of plant material from the prehistoric times is required to produce one gallon of gasoline for our gas powered vehicles.

### What are the Benefits of Fossil Fuels?

Fossil fuels allow us to easily live with luxuries such as: electricity, heat, and transportation, among others. Fossil fuels are relatively inexpensive, which makes fuels for electricity, heating, and transportation available to a greater amount of people. Fossil fuels are also easily transported though various pipelines set up around the world, not to mention fossil fuels follow a straightforward combustion process.

Fuel + Oxygen ---> Heat + Water + Carbon Dioxide + Nitrogen

A good way to compare various fuels is through their heats of combustion: the best fuel has the highest heat of combustion. Fossil fuels yield the most energy per unit of mass in comparison to other sources of energy, as seen in the "Heat of Combustion" table below.

Fuel kJ/g
Municipal Waste -12.7
Cellulose -17.5
Pinewood -21.2
Methanol -22.7
Bituminous coal -28.3
Isooctane (component of gasoline) -47.8
Natural gas -49.5

### What are the Limitations of Fossil Fuels?

Fossil fuels a scarce energy resource--since it takes around 300 million years to renew, and the worlds consumption of this hot commodity does not show any drop off in the near future. It is uncertain when our supply of fossil fuels will be completely depleted, but has been estimated to be within the next 100 years.

Fossil fuels have also taken a toll on the environment. Although fossil fuels follow a straightforward combustion process, the carbon dioxide emitted into the atmosphere is rather harmful to the environment.  Fossil fuels such as oil, natural gas, and coal often contain sulfur compounds.  When burned, the sulfur is oxidized to sulfur dioxide, SO2.  When sulfur dioxide comes into contact with water, it can convert to sulfurous acid, H2SO3, causing corrosive acid rain.  Nitrogen oxides, NOx, also contribute to acid rain.  The combustion of fossil fuels, has contributed to global warming  and acid rain. Check out this video to learn more about the effects of fossil fuels on the environment.

### References

• Petrucci, et al. General Chemistry: Principles & Modern Applications. 9th ed. Upper Saddle River, New Jersey 2007.
• Diane Gibson, Fossil Fuels. North Mankato, Minn: Smart Apple Media, 2001.
• Natural Gas
• Oil
• Coal

Unlike fossil fuels, the wind and sun are in no danger of running out in the next 100 years.

• Solar Energy
• Wind-power
• Biofuels
• Hydrogen Fuel
• Check out this cool of a purely hydrogen fuel cell powered plane!

### Contributors

• Rebecca Davidson