Ch.18 - Chemistry of the Environment

Problem 25

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Chapter 18, Problem 25

(a) What is the difference between chlorofluorocarbons and hydrofluorocarbons?

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Understand the basic structure of chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFCs). CFCs contain carbon, chlorine, and fluorine atoms, while HFCs contain carbon, hydrogen, and fluorine atoms.

Recognize that the presence of chlorine in CFCs makes them more harmful to the ozone layer compared to HFCs, which do not contain chlorine.

Note that CFCs were widely used in refrigeration, air conditioning, and as propellants in aerosol sprays, but their production has been largely phased out due to their ozone-depleting potential.

Understand that HFCs were developed as a replacement for CFCs because they do not deplete the ozone layer, although they are potent greenhouse gases.

Consider the environmental impact of both compounds: CFCs contribute to ozone depletion, while HFCs contribute to global warming, leading to ongoing research for more sustainable alternatives.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Chlorofluorocarbons (CFCs)

Chlorofluorocarbons are organic compounds that contain chlorine, fluorine, and carbon. They were commonly used as refrigerants, propellants, and solvents. However, CFCs are known to deplete the ozone layer, leading to increased UV radiation reaching the Earth's surface. Due to their environmental impact, many CFCs have been phased out under international agreements like the Montreal Protocol.

Hydrofluorocarbons (HFCs)

Hydrofluorocarbons are a class of compounds that contain hydrogen, fluorine, and carbon. Unlike CFCs, HFCs do not contain chlorine and therefore do not deplete the ozone layer. They are often used as substitutes for CFCs in refrigeration and air conditioning. However, HFCs are potent greenhouse gases, contributing to global warming, which has led to calls for their regulation and reduction.

Environmental Impact

The environmental impact of chemical compounds like CFCs and HFCs is crucial for understanding their use and regulation. CFCs contribute to ozone layer depletion, which increases UV radiation exposure, while HFCs, although ozone-friendly, are significant greenhouse gases. Understanding these impacts is essential for evaluating the sustainability of these compounds and the need for alternatives in industrial applications.

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Textbook Question

The ultraviolet spectrum can be divided into three regions based on wavelength: UV-A (315–400 nm), UV-B (280–315 nm), and UV-C (100–280 nm). (b) In the absence of ozone, which of these three regions, if any, are absorbed by the atmo- sphere?

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Open Question

Do the reactions involved in ozone depletion involve changes in the oxidation state of the O atoms? Explain.

Textbook Question

Which of the following reactions in the stratosphere cause an increase in temperature there? (a) O(g) + O2(g) → O3+(g) (b) O3*(g) + M(g) → O3(g) + M*(g) (c) O2(g) + hv → 2 O(g) (d) O(g) + N2(g) → NO(g) + N(g) (e) All of the above

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Open Question

Draw the Lewis structure for the chlorofluorocarbon CFC-11, CFCl3. What chemical characteristics of this substance allow it to effectively deplete stratospheric ozone?

Open Question

The average bond enthalpies of the C ¬ F and C ¬ Cl bonds are 485 kJ/mol and 328 kJ/mol, respectively. Given the fact that O2, N2, and O in the upper atmosphere absorb most of the light with wavelengths shorter than 240 nm, would you expect the photodissociation of C ¬ F bonds to be significant in the lower atmosphere?

Textbook Question

(a) When chlorine atoms react with atmospheric ozone, what are the products of the reaction?

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