The Greenhouse effect and Acid rain

How is the greenhouse effect caused?

1. Electromagnetic radiation at most wavelengths passes through the Earth's atmosphere.

2. The Earth absorbs most of the radiation and warms up.

3. The Earth radiates energy as infrared radiation.

4. Some of the infrared radiation goes into space.

5. Some of the infrared radiation is absorbed by greenhouse gases in the atmosphere.

6. The lower atmosphere warms up.

How is acid rain caused (Sulfur Dioxide and Sulfuric Acid)?

1. Sulfur impurities: in fossil fuels like coal and oil are oxidized when the fuel is burned. 

2. Sulfur dioxide (SO₂) gas is produced . 

3. This SO₂ rises into the atmosphere. 

4. In the clouds, SO₂ reacts with water to form sulfuric acid (H₂SO₄). 

• Word equation: Sulfur dioxide + Water → Sulfuric acid

• Chemical equation: SO₂(g) + H₂O(l) → H₂SO₄(aq) 

How is acid rain caused (Nitrogen oxides and nitric acid)?

1. Nitrogen and oxygen: in the air combine at high temperatures found in vehicle engines and power stations to form nitrogen oxides (NOx).

2. Nitrogen dioxide (NO₂) is a key component of NOx .

3. This NO₂ then reacts with water in the atmosphere to form nitric acid (HNO₃).

   • Word equation: Nitrogen dioxide + Water → Nitric acid

   • Chemical equation: 2NO₂(g) + H₂O(l) → HNO₃(aq) + HNO₂(aq)

What impact does acid rain have on the environment?

Acid rain negatively impacts the environment by acidifying lakes and streams, killing aquatic life, and harming forests by damaging trees and leaching essential soil nutrients. It also releases toxic aluminum into soils and waterways, weakening plants and making water sources unsuitable for consumption. Additionally, acid deposition damages man-made structures, such as buildings and monuments, particularly those made of marble.

What impact does the greenhouse effect have on the environment?

The enhanced greenhouse effect causes global warming, which leads to rising sea levels, more extreme weather events like heatwaves and floods, melting glaciers, shifts in plant and animal habitats, increased risks of flooding and drought, and the spread of tropical diseases. While the natural greenhouse effect is essential for life, human activities have increased greenhouse gases, intensifying this process and altering Earth's climate balance.

What measures are taken to try and reduce the impact of the greenhouse effect? 

Decreasing carbon dioxide (CO2) and methane (CH4) emissions through renewable energy sources and improved energy efficiency, while promoting the use of alternative fuels and developing carbon capture-and-storage (CCS) technologies. Chemically, this involves developing better catalysts to lower reaction temperatures/pressures, recycling materials to reduce energy-intensive extraction, and utilizing biofuels that absorb CO2 during growth.

What measures are taken to try and reduce the impact of acid rain? 

Measures to reduce acid rain's impact include reducing sulfur dioxide (SO2) and nitrogen oxides (NOx) emissions through flue gas desulfurization and catalytic converters, promoting renewable energy sources and energy efficiency, using low-sulfur fuels, and applying liming to acidified soils and lakes to neutralize acidity.

What are the two primary acidic gases responsible for acid rain, and form what sources do they originate? 

1. Sulfur Dioxide (SO₂) - Coal and crude oil when it combusts in power stations, industrial furnaces and some vehicles and then reacts with oxygen. 

2. Nitrogen Oxides (NO_x), primarily nitric oxide (NO) and nitrogen dioxide (NO₂) - Formed during high temperature combustion processes, particularly in internal combustion engines (cars, lorries) and power station boilers. At these elevated temperatures, the normally unreactive nitrogen (N₂) present in the air reacts with oxygen. Nitrogen Dioxide then reacts with water and oxygen in the atmosphere to form nitric acid (HNO₃).

What is the equation for the production of sulfur dioxide? 

S(s) + O₂(g) → SO₂(g)

What is the equation for the production of sulfuric acid? 

2SO₂(g) + O₂ → 2SO₃(g)

SO₃(g) + H₂O → H₂SO₄(aq)

What is the equation for the production of Nitrogen dioxide?

N₂ + O₂ → 2NO(g)

2NO(g) + O₂(g) → 2NO₂(g)

What is the equation for the production of Nitric acid?

4NO₂(g) + O₂ + 2H₂O(l) → 4HNO₃(aq)

Describe at least three distinct environmental impacts of acid rain.

1. Damage to aquatic life

• Acid rain makes rivers, lakes, and streams more acidic.

• This lowers the pH of the water, which can kill fish and other aquatic organisms.

• Some species cannot survive if the pH drops below a certain level, so biodiversity decreases.

2. Harm to plants and trees

• Acid rain damages leaves and reduces a plant’s ability to photosynthesise.

• It also washes away essential nutrients and minerals (like magnesium and calcium) from the soil.

• This weakens trees and crops, making them more vulnerable to disease and extreme weather.

3. Corrosion of buildings and monuments

• Acid rain reacts with calcium carbonate in limestone and marble, gradually wearing away stone buildings, statues, and monuments.

• It also speeds up the rusting of metals.

• This leads to costly repairs and loss of cultural heritage.

Explain the chemical principle behind how a catalytic converter reduces nitrogen oxide emissions.

• Primarily used in vehicles, catalytic converters are devices placed in the exhaust system that reduce the emission of harmful pollutants, including nitrogen oxides.

• They contain a ceramic honeycomb structure coated with precious metals like platinum, palladium, and rhodium, which act as catalysts.

• In a redox reaction, nitrogen oxides are reduced back to nitrogen gas and oxygen.

Outline the process of flue gas desulfurisation, including the main reactants and a useful byproduct.

• This technology is widely employed in large industrial plants and power stations that burn fossil fuels, especially coal, to remove sulphur dioxide from the exhaust gases (flue gases) before they are released into the atmosphere.

• The most common method involves a wet scrubbing process using a slurry of limestone (calcium carbonate) or lime (calcium hydroxide). 

Process:

• Waste gases (containing SO₂) are passed through a slurry of alkaline materials such as calcium oxide (CaO) or calcium carbonate (CaCO₃).

• The SO₂ reacts with the base to form calcium sulphite (CaSO₃):

  CaO(s)+SO₂(g)  →  CaSO₃(s)

• The calcium sulphite can be further oxidised with oxygen to make calcium sulphate (CaSO₄), also known as gypsum:

  2CaSO₃(s)+O2(g)  →  2CaSO₄(s)

Useful Byproduct:

• Calcium sulphate (gypsum) is obtained, which is used in the manufacture of plasterboard and cement.

• This turns a pollutant into a valuable construction material.

Differentiate between the greenhouse effect and global warming.

Greenhouse Effect - Natural process where gases trap heat, keeping the Earth warm

Global Warming - Rise in Earth’s temperature due to excess green house gases from human activities.

Outline the main anthropogenic sources of Carbon dioxide (CO₂). Briefly describe a chemical process or industrial activity that leads to its emission.

Main sources:

• Combustion of fossil fuels (coal, oil, natural gas) for energy and transport.

• Cement production also releases CO₂ when limestone is decomposed.

Chemical process:

• Complete combustion of hydrocarbons:

  CH₄ + 2O₂ → CO₂ + 2H₂O

• Decomposition of limestone in cement manufacture:

  CaCO₃(s) → CaO(s) + CO₂(g)

Outline the main anthropogenic sources of methane (CH₄). Briefly describe a chemical process or industrial activity that leads to its emission.

Main sources:

• Agriculture (especially from ruminant animals like cows, via enteric fermentation).

• Landfills, where anaerobic decomposition of organic waste produces CH₄.

• Fossil fuel extraction (leaks from natural gas and oil production).

Chemical/biological process:

• Anaerobic decay of organic matter by microorganisms:

  Organic Matter → CH₄ + CO₂

(ontop of the arrow there should be anaerobic bacteria)

Outline the main anthropogenic sources of Nitrous oxide (N₂O). Briefly describe a chemical process or industrial activity that leads to its emission.

Main sources:

• Agricultural soils from overuse of nitrogen-based fertilisers.

• Industrial processes (e.g., production of nitric acid, used in fertilisers).

• Some emissions from vehicle engines.

Chemical process:

• In soils, bacteria reduce nitrates in fertilisers:

  2NO₃⁻→  N₂O+O₂

• In industry, N₂O is a byproduct when ammonia is oxidised to make nitric acid:

  4NH₃+5O₂ →  4NO+6H₂O

(N2O  as byproduct)