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Chemistry of the Environment - Greenhouse effect and climate change

Grade 11IGCSEChemistry

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The Greenhouse Effect is a natural process where greenhouse gases like CO2CO_2 and CH4CH_4 trap heat in the atmosphere. Short-wavelength radiation from the sun passes through the atmosphere, but long-wavelength infrared radiation reflected from the Earth's surface is absorbed by these gases.

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Carbon Dioxide (CO2CO_2) is primarily released into the atmosphere through the respiration of living organisms and the complete combustion of carbon-based fuels (fossil fuels).

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Methane (CH4CH_4) is a potent greenhouse gas produced by the decomposition of vegetation and as a waste product from the digestive systems of livestock (e.g., cattle).

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The enhanced greenhouse effect is caused by increased concentrations of greenhouse gases due to human activity, leading to global warming, which results in rising sea levels, melting ice caps, and extreme weather patterns.

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Photosynthesis is the process by which green plants remove CO2CO_2 from the atmosphere to produce glucose (C6H12O6C_6H_{12}O_6), helping to regulate the carbon cycle.

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Atmospheric composition: The Earth's atmosphere consists of approximately 78%78\% Nitrogen (N2N_2), 21%21\% Oxygen (O2O_2), and small amounts of Noble gases and CO2CO_2 (approx. 0.04%0.04\%).

📐Formulae

6CO2+6H2O→lightC6H12O6+6O26CO_2 + 6H_2O \xrightarrow{light} C_6H_{12}O_6 + 6O_2

C6H12O6+6O2→6CO2+6H2O+energyC_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy}

CH4+2O2→CO2+2H2OCH_4 + 2O_2 \rightarrow CO_2 + 2H_2O

2C8H18+25O2→16CO2+18H2O2C_8H_{18} + 25O_2 \rightarrow 16CO_2 + 18H_2O

💡Examples

Problem 1:

Explain how the combustion of fossil fuels contributes to the greenhouse effect and provide a balanced equation for the complete combustion of propane (C3H8C_3H_8).

Solution:

C3H8+5O2→3CO2+4H2OC_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O

Explanation:

Combustion releases CO2CO_2, a greenhouse gas. This gas absorbs thermal infrared radiation emitted from the Earth, preventing it from escaping into space, thereby increasing the Earth's average temperature.

Problem 2:

State two human activities that increase the concentration of methane (CH4CH_4) in the atmosphere.

Solution:

  1. Increased livestock farming (e.g., cattle). 2. Decomposition of organic waste in landfill sites.

Explanation:

Methane is produced by anaerobic bacteria during the decomposition of organic matter and during the digestive processes of ruminant animals.

Problem 3:

Calculate the mass of CO2CO_2 produced when 16g16\text{g} of methane (CH4CH_4) is burnt completely in oxygen.

Solution:

1 mole of CH4CH_4 (16g16\text{g}) produces 1 mole of CO2CO_2 (44g44\text{g}). Therefore, 44g44\text{g} of CO2CO_2 is produced.

Explanation:

Using the equation CH4+2O2→CO2+2H2OCH_4 + 2O_2 \rightarrow CO_2 + 2H_2O, the molar ratio of CH4CH_4 to CO2CO_2 is 1:11:1. Since the molar mass of CH4CH_4 is 12+(4×1)=16g/mol12 + (4 \times 1) = 16\text{g/mol} and CO2CO_2 is 12+(2×16)=44g/mol12 + (2 \times 16) = 44\text{g/mol}.

Greenhouse effect and climate change Revision - Grade 11 Chemistry IGCSE