The Amount of Carbon Dioxide Produced When Fuels Burn (DP IB Chemistry)

The Amount of Carbon Dioxide Produced When Fuels Burn

Fossil fuels

What is a fossil fuel?

• A fossil fuel is a material such as coal, oil and natural gas

• Fossil fuels contain hydrocarbons

• They were formed naturally in the Earth's crust from the remains of dead plants and animals millions of years ago

• They are described as non-renewable or finite because they cannot be replaced in a short period of time

Advantages of fossil fuels

Coal

• Relatively cheap

• Abundant 

• Long lifespan (compared to other fossil fuels)

• Can be converted into liquid fuels and gases

• Relatively safe

• Products from the combustion of coal have other uses, e.g. ash can be used to make roads

Oil

• Easy to store and transport in pipelines and tankers

• Impurities can be easily removed

• Releases a lot of energy per kg

  • Known as high energy / enthalpy density

• Easily processed

  • Fractional distillation and cracking are used to produce other useful chemicals, e.g. shorter-chain alkanes and alkenes 

Natural gas

• Cheapest of the fossil fuels

• Easy to store and transport in pipelines and pressurised containers

• Large amounts of energy per unit mass

  • Known as high specific energy

• Relatively clean

  • Complete combustion of natural gas happens with a blue flame producing minimal to no harmful compounds

  • Does not contribute to acid rain

Disadvantages of fossil fuels

• All fossil fuels have limited lifespans / supplies, i.e are finite 

Coal

• Combustion produces large amounts of pollution

  • Carbon dioxide

  • Sulfur dioxide 

  • Particulates 

• Associated with:

  • Global warming

  • Acid rain

  • Global dimming / visual pollution

• Difficult to transport 

• Issues around mining:

  • Destruction of habitats

  • Noise pollution

  • Health of miners

  • Safety issues 

• Potentially radioactive

Oil

• Combustion produces large amounts of pollution, including:

  • Carbon dioxide 

  • Sulfur dioxide 

  • Carbon monoxide 

• Associated with:

  • Global warming

  • Acid rain

  • Global dimming / visual pollution

  • Photochemical smog

• Uneven worldwide distribution 

• Oil spills affecting habitats

• Safety issues around drilling

Natural gas

• Combustion produces large amounts of pollution

  • Carbon dioxide 

• Associated with:

  • Global warming

• Expensive and time-intensive to produce

• Expensive to store

• Safety issues around storage in pressurised containers

Burning fuels

• Many different fuels are used in everyday life

  • The choice of fuel used can depend on:

    • Availability of the fuel

    • Cost

    • Intended use

    • Energy requirements 

• All fuels can undergo combustion to release the chemical energy stored within their bonds 

  • Specific energy is a measure of the energy stored in a substance 

The specific energy of different common fuels

Different fuels release different amounts of energy when combusted

• It is the hydrocarbon contained within the fossil fuel (and other fuels) that undergoes combustion

• Remember: Complete combustion of hydrocarbons results in the production of carbon dioxide and water, while incomplete combustion results in the production of carbon monoxide / carbon and water

  • Both types of combustion are exothermic, so they release energy

•  As the length of the hydrocarbon chain increases

  • There is an increased carbon content resulting in the production of more carbon dioxide and carbon monoxide / carbon

  • There are stronger London dispersion forces, which makes the hydrocarbon less volatile

  • The hydrocarbon releases less energy per unit mass of fuel

Graph showing the mass of carbon dioxide and amount of energy released during the combustion of the first eight straight-chain alkanes  

As the length of the hydrocarbon chain increases, more carbon dioxide and less energy is released per gram of hydrocarbon burnt

• As the length of the hydrocarbon increases, it is also more likely that incomplete combustion will take place