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

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