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Chemistry of the Environment - Greenhouse effect and global warming

Grade 12IGCSEChemistry

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 in the atmosphere trap heat, maintaining Earth's temperature at a level capable of supporting life.

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Greenhouse gases include Carbon dioxide (CO2CO_2), Methane (CH4CH_4), Nitrous oxide (N2ON_2O), and water vapor (H2OH_2O).

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The mechanism involves short-wavelength electromagnetic radiation (visible light and UV) from the Sun passing through the atmosphere and being absorbed by the Earth's surface.

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The Earth re-emits this energy as long-wavelength infrared (IRIR) radiation. Greenhouse gases absorb this IRIR radiation and re-radiate it in all directions, including back toward the surface.

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Global Warming refers to the increase in the Earth's average surface temperature due to an 'enhanced' greenhouse effect caused by human activities (anthropogenic factors).

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Major sources of CO2CO_2 include the combustion of fossil fuels (coal, oil, and gas) and deforestation, which reduces the rate of photosynthesis (6CO2+6H2O→C6H12O6+6O26CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2).

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Major sources of CH4CH_4 include livestock farming (digestive processes of cattle), rice paddies, and the decomposition of organic waste in landfills.

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Consequences of global warming include rising sea levels due to melting polar ice caps and thermal expansion of oceans, more frequent extreme weather events, and loss of biodiversity.

📐Formulae

6CO2+6H2O→lightC6H12O6+6O26CO_2 + 6H_2O \xrightarrow{\text{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:

Calculate the mass of Carbon dioxide (CO2CO_2) produced when 160 g160\text{ g} of Methane (CH4CH_4) is completely burned in oxygen.

Solution:

  1. Write the balanced equation: CH4+2O2→CO2+2H2OCH_4 + 2O_2 \rightarrow CO_2 + 2H_2O 2. Calculate moles of CH4CH_4: n(CH4)=massMr=160 g16 g/mol=10 moln(CH_4) = \frac{\text{mass}}{M_r} = \frac{160\text{ g}}{16\text{ g/mol}} = 10\text{ mol} 3. Use the molar ratio (1:11:1): n(CO2)=10 moln(CO_2) = 10\text{ mol} 4. Calculate mass of CO2CO_2: mass=n×Mr=10 mol×44 g/mol=440 g\text{mass} = n \times M_r = 10\text{ mol} \times 44\text{ g/mol} = 440\text{ g}

Explanation:

According to the stoichiometry of the combustion reaction, one mole of methane produces one mole of carbon dioxide. Therefore, 160 g160\text{ g} of CH4CH_4 results in 440 g440\text{ g} of CO2CO_2 being released into the atmosphere.

Problem 2:

Explain why Methane (CH4CH_4) is considered a more potent greenhouse gas than Carbon dioxide (CO2CO_2) even though its concentration is lower.

Solution:

Methane has a higher 'Global Warming Potential' (GWPGWP). It is approximately 25−3025-30 times more effective at trapping infrared radiation in the atmosphere than CO2CO_2 over a 100-year period.

Explanation:

Potency is determined by the molecule's ability to absorb specific wavelengths of IRIR radiation and its atmospheric lifetime. While CO2CO_2 is more abundant, the molecular structure of CH4CH_4 allows it to absorb thermal energy more efficiently.

Greenhouse effect and global warming Revision - Grade 12 Chemistry IGCSE