2425 Chemistry Topic 2 - Air Notes

Air Composition

• Clean dry air is composed primarily of:

  • Nitrogen: 78%

  • Oxygen: 21%

  • Noble gases and Carbon dioxide make up the remainder.

Separation of Gases

• Fractional Distillation of Liquefied Air is the process used for separating nitrogen from oxygen in the air.

Air Pollutants

Sources of Air Pollutants

• Sulfur Dioxide:

  • From combustion of fossil fuels containing sulfur compounds.

• Oxides of Nitrogen:

  • Emitted from car engines.

• Carbon Monoxide and Particulates:

  • Produced from incomplete combustion of carbon-containing fuels.

• Carbon Dioxide:

  • Resulting from complete combustion of carbon-containing fuels.

• Methane:

  • Released from decomposition of vegetation and waste gases from digestion in animals.

Adverse Effects of Air Pollutants

1. Sulfur Dioxide

• A poisonous gas that irritates the respiratory tract and causes breathing difficulties.

• Causes acid rain.

2. Oxides of Nitrogen

• Contributes to acid rain and photochemical smog.

• Leads to respiratory problems.

3. Carbon Monoxide

• A toxic gas that binds to hemoglobin, reducing the ability of blood cells to carry oxygen, which may lead to asphyxiation.

4. Particulates

• Increase the risk of respiratory issues and cancer.

5. Carbon Dioxide

• Higher concentrations contribute to global warming and climate change.

6. Methane

• A potent greenhouse gas affecting the atmosphere and contributing to climate change.

Photochemical Smog

• Occurs in high automobile traffic areas and does not involve smoke or fog.

• Caused by sunlight-catalyzed reactions between:

  • Nitrogen oxides and unburnt hydrocarbons – resulting in ozone production (toxic gas).

• Effects:

  • Reduces visibility.

  • Causes plant damage.

  • Leads to eye irritation and respiratory distress.

Acid Rain

• Formed when sulfur dioxide reacts with water in the air, producing sulfuric acid, and when nitrogen oxides react with water, producing nitric acid.

• Normal rain has a pH of 5.5 whereas acid rain has a pH of around 4.

Problems Caused by Acid Rain

• Corrodes metal structures and damages buildings/art statues (erosion of limestone and marble).

• Increases water acidity, risking fish and aquatic life health.

• Affects plant growth through acid rain absorption and mineral leaching.

Challenges of Reducing Emissions

• High costs and geographical discrepancies between emission sources and rainfall areas.

Greenhouse Gases and Global Warming

• Carbon dioxide and methane are key contributors to the greenhouse effect, increasing Earth's average temperature.

• Global warming leads to unpredictable climate changes, affecting weather patterns and sea levels.

Greenhouse Effect Mechanism

• Energy from the Sun warms the Earth during the day.

• At night, the Earth releases heat as infrared radiation.

• Greenhouse gases (CO2, CH4, and others) trap heat in the atmosphere, preventing it from escaping into space, thus increasing surface temperatures.

Oxides of Nitrogen Formation

• Produced in car engines under high temperature and pressure when nitrogen reacts with oxygen.

Strategies to Reduce Air Pollutants

Climate Change Reduction Plans

• Increased tree planting.

• Reduction in livestock farming.

• Decreased use of fossil fuels through alternative energy sources (renewable energy).

Acid Rain Mitigation Strategies

• Reducing sulfur dioxide emissions.

• Installation of flue gas desulfurization systems to remove harmful emissions from factory output.

• Use of low-sulfur fuels.

• Implementation of catalytic converters in vehicles to convert harmful emissions into less harmful substances.

Catalytic Converters

Function

• Convert:

  • Carbon monoxide to carbon dioxide.

  • Oxides of nitrogen to nitrogen.

  • Hydrocarbons to carbon dioxide and water.

Chemical Reactions

1. 2CO(g) + O2(g) → 2CO2(g)

2. 2CO(g) + 2NO(g) → 2CO2(g) + N2(g)

3. 2NO2(g) + 4CO → 4CO2(g) + N2(g)

4. Hydrocarbons + nitrogen monoxide → carbon dioxide + nitrogen + water.

• Catalytic converters work best at high temperatures and have large surface areas.

Note

• Catalytic converters can be poisoned by lead.

Photosynthesis

• Process by which plants create food by absorbing carbon dioxide and water using sunlight energy, resulting in glucose and oxygen.

• Equation:

  • 6CO2(g) + 6H2O(l) + sunlight energy → C6H12O6(s) + 6O2(g)

Respiration

• The "burning" of food to release energy, producing carbon dioxide and water as by-products.

• Equation:

  • C6H12O6(s) + 6O2(g) → 6CO2(g) + 6H2O(l) + Energy

Comparison

• Photosynthesis is an endothermic process, while respiration is exothermic.