Carbon Dioxide & Sulfur Dioxide Emissions (WJEC GCSE Chemistry)

• The combustion of non-renewable fossil fuels is the major source of atmospheric pollution
  • These include coal, oil and natural gas
• Crude oil is processed by fractional distillation to produce various fuels including petrol, diesel and kerosene 
• There are finite amounts of fossil fuels and they all contribute to atmospheric pollution and global warming
• All of these fossil fuels contain carbon, hydrogen and small quantities of sulfur
• The combustion of fossil fuels releases water vapour, carbon dioxide and sulfur dioxide

Forming carbon dioxide

• When fuels are combusted, the carbon and hydrogen contained within them are oxidised to carbon dioxide and water
  • For example, the combustion equation for propane is:

C₃H₈ + 5O₂ → 3CO₂ + 4H₂O

• Increasing levels of carbon dioxide are causing significant upset to the Earth’s natural conditions by trapping extra heat energy
  • Even though carbon dioxide is only about 0.04% of the Earth's atmosphere
• This process is called the greenhouse effect

How carbon dioxide affects the environment

Carbon dioxide is a greenhouse gas that traps some of the Sun's radiation causing the Earth to warm up

Consequences of the greenhouse effect

• The vast majority of climate scientists agree that increasing levels of greenhouse gases are causing the average temperature of the Earth to increase
• Temperature increases are leading to climate change
  • Climate change is a long-term shift in worldwide weather patterns and conditions
• The consequences of climate change include:
  • Rising Sea Levels
    • Due to the melting of the polar ice caps and glaciers 
    • This can increase flooding 
  • Loss of habitats for birds, fish and plants 
  • More extreme weather, e.g. storms, extreme heatwaves and changing rainfall patterns 
  • More drought conditions
    • Some areas are seeing devastating droughts leading to crop failure and the collapse of the agricultural industry

Forming sulfur dioxide

• Fossil fuels are often contaminated with small amounts of sulfur impurities
• When these contaminated fossil fuels are combusted, the sulfur in the fuels get oxidised to sulfur dioxide

S (s) + O₂ (g) → SO₂ (g)

• Sulfur dioxide may be further oxidised to sulfur trioxide

2SO₂ (g) + O₂ (g) ⇌ 2SO₃ (g)

• The sulfur dioxide and sulfur trioxide then dissolve in rainwater droplets to form sulfurous acid and sulfuric acid

SO₂ (g) + H₂O (l) → H₂SO₃ (aq)

SO₃ (g) + H₂O (l) → H₂SO₄ (aq)

• These acids are components of acid rain which has several damaging impacts on the environment

How sulfur dioxide affects the environment

Sulfur dioxide forms acid rain which affects the environment

Effects and consequences of acid rain

• Clean rain is weakly acidic with a pH of 5.5, while acid rain has a pH in the range of 2 - 4
• Acid rain can react with metals and rocks (such as limestone and marble) causing buildings and statues to get damaged
• Limestone and marble both contain calcium carbonate
• The consequence of calcium carbonate reacting with acid rain is stonework corrodes and weakens:

CaCO₃ (s)  + H₂SO₄ (aq)  →  CaSO₄ (aq)  +  CO₂ (g)  +  H₂O (l)

• Again the consequence of metallic structures, such as iron bridges, reacting with acid rain is that the structures corrode and weaken:

Fe (s)  + H₂SO₄ (aq) →  FeSO₄ (aq)  +  H₂ (g)

The effect of acid rain on structures

Acid rain affects buildings, statues and metallic structures, particularly in polluted cities

• Acid rain can fall directly onto plants and leaves
  • The consequence is that plants and leaves are damaged and can lead to the death of the plant

The effect of acid rain on plant life

Acid rain directly affects plants by damaging the leaves and roots

• Acid rain can fall into rivers and lakes causing a decrease in pH
  • The consequence of this change in acidity is that marine / aquatic life is affected and can ultimately die