Reactivity 1.3 – Energy from fuels

1.3.3 – Fossil fuels

📌 Fuels

  • Ideal fuels are ones that produce a great amount of energy and minimal pollution
  • Fossil fuels are non-renewable energy sources
  • Wood is a renewable energy source
  • Fossil fuels have become a very widely used source of energy because of their high energy density (energy produced per unit volume) and their cheap cost and wide accessibility
  • Fossil fuels are the result of decomposition of organic compounds

📌 Common fossil fuels

  1. Coal : The most abundantly used fossil fuel
  • Coal is the most widely used fossil fuel as it is 80-90% carbon by mass and has a high energy density
  • It is a combustible sedimentary rock that is widely available

2. Crude oil : a composite mixture of several organic compounds

  • Formed from the remains marine animals from millions of years ago
  • Organic matter decayed due to bacteria and a lack of oxygen
  • Crude oil is a limited resource

3. Natural gas : a mix of several gases – mainly methane

  • Contains nitrogen and sulfur compounds in addition to methane
  • Gas is trapped in geological formations
  • It is highly explosive when in contact with air
  • Low carbon content, therefore it is the ‘cleanest’ fossil fuel

📌 Combustion of alkanes

  • Hydrocarbons with higher carbon content are mosre likely to undergo incomplete combustion
  • Higher alkanes have a lower energy released per unit mass
  • Thus we can also infer that coal (greatest carbon content) is the most polluting and ‘dirtiest’ fuel to burn
  • Higher percentage of carbon content also means that the specific energy (energy produced per unit mass) is lower

📌 Greenhouse effect

  • The greenhouse effect is the process by which gases in the atmosphere trap heat on Earth
  • Increased carbon dioxide levels due to increase burning of fossil fuels has contributed significantly to the greenhouse effect
  • Greenhouse gases absorb long-wave radiation and allow short-wave radiation to pass through the atmosphere
  • Vibrations in CO2 molecules during infrared radiation absorption allow the radiation to be ‘re-radiated’ back to the Earth’s surface, thus increasing global temperature
  • Therefore, the increase in CO2 has contributed significantly to global warming