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Environmental Chemistry - Ozone Depletion and Global Warming

Grade 11ICSEChemistry

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

πŸ”‘Concepts

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The Ozone layer is located in the stratosphere (between 1010 to 5050 km above sea level) and protects the Earth from harmful UVβˆ’BUV-B and UVβˆ’CUV-C radiation.

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Ozone depletion is primarily caused by Chlorofluorocarbons (CFCsCFCs), also known as Freons, which are stable in the troposphere but break down in the stratosphere under UVUV radiation.

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The 'Ozone Hole' is a phenomenon observed mainly over Antarctica during the spring, facilitated by Polar Stratospheric Clouds (PSCsPSCs) which provide a surface for chlorine activation.

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Global Warming is the gradual increase in the average temperature of the Earth's atmosphere due to the Greenhouse Effect.

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Major Greenhouse Gases (GHGsGHGs) include Carbon dioxide (CO2CO_2), Methane (CH4CH_4), Nitrous oxide (N2ON_2O), Chlorofluorocarbons (CFCsCFCs), and Water vapor (H2OH_2O).

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The Greenhouse Effect occurs when shorter wavelength solar radiation passes through the atmosphere but the longer wavelength infrared (heat) radiation emitted by the Earth is trapped by GHGsGHGs.

πŸ“Formulae

CF2Cl2(g)β†’hΞ½CΛ™F2Cl(g)+Clβˆ™(g)CF_2Cl_2(g) \xrightarrow{h\nu} \dot{C}F_2Cl(g) + Cl^{\bullet}(g)

Clβˆ™(g)+O3(g)β†’ClOβˆ™(g)+O2(g)Cl^{\bullet}(g) + O_3(g) \rightarrow ClO^{\bullet}(g) + O_2(g)

ClOβˆ™(g)+O(g)β†’Clβˆ™(g)+O2(g)ClO^{\bullet}(g) + O(g) \rightarrow Cl^{\bullet}(g) + O_2(g)

NO(g)+O3(g)β†’NO2(g)+O2(g)NO(g) + O_3(g) \rightarrow NO_2(g) + O_2(g)

NO2(g)+O(g)β†’NO(g)+O2(g)NO_2(g) + O(g) \rightarrow NO(g) + O_2(g)

πŸ’‘Examples

Problem 1:

Explain the role of CFCsCFCs in the depletion of the ozone layer using chemical equations.

Solution:

In the stratosphere, CFCsCFCs are broken down by UVUV radiation to release chlorine free radicals: CFCl3β†’hΞ½CΛ™FCl2+Clβˆ™CFCl_3 \xrightarrow{h\nu} \dot{C}FCl_2 + Cl^{\bullet}. These Clβˆ™Cl^{\bullet} radicals react with ozone: Clβˆ™+O3β†’ClOβˆ™+O2Cl^{\bullet} + O_3 \rightarrow ClO^{\bullet} + O_2. The ClOβˆ™ClO^{\bullet} then reacts with atomic oxygen to regenerate the chlorine radical: ClOβˆ™+Oβ†’Clβˆ™+O2ClO^{\bullet} + O \rightarrow Cl^{\bullet} + O_2.

Explanation:

One chlorine radical can destroy thousands of ozone molecules because it is regenerated in the process, acting as a catalyst.

Problem 2:

Calculate the net reaction of ozone depletion by Nitric Oxide (NONO).

Solution:

Step 1: NO+O3→NO2+O2NO + O_3 \rightarrow NO_2 + O_2 Step 2: NO2+O→NO+O2NO_2 + O \rightarrow NO + O_2 Net Reaction: O3+O→2O2O_3 + O \rightarrow 2O_2

Explanation:

Nitric oxide released from supersonic jets acts as a catalyst, similar to chlorine radicals, resulting in the conversion of ozone and atomic oxygen into molecular oxygen.

Problem 3:

Why is CO2CO_2 considered the most significant greenhouse gas even though CH4CH_4 has a higher Global Warming Potential (GWPGWP)?

Solution:

Although CH4CH_4 is about 2525 times more effective at trapping heat than CO2CO_2, the concentration of CO2CO_2 in the atmosphere is much higher (Β 415~415 ppm) compared to CH4CH_4 (Β 1.8~1.8 ppm).

Explanation:

The total contribution to global warming depends on both the efficiency of the gas (GWP) and its abundance in the atmosphere.

Ozone Depletion and Global Warming Revision - Class 11 Chemistry ICSE