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Ch.18 - Chemistry of the Environment
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
All textbooksBrown 14th EditionCh.18 - Chemistry of the EnvironmentProblem 82b
Chapter 18, Problem 82b

The concentration of H2O in the stratosphere is about 5 ppm. It undergoes photodissociation according to: H2O(g) → H(g) + OH(g) (b) Using Table 8.3, calculate the wavelength required to cause this dissociation.

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Identify the reaction: \( \text{H}_2\text{O} \rightarrow \text{H} + \text{OH} \). This is a photodissociation reaction where water is broken down into hydrogen and hydroxyl radicals.
Determine the bond energy required to break the \( \text{O-H} \) bond in water. Use Table 8.3 to find the bond dissociation energy for \( \text{O-H} \).
Convert the bond energy from kilojoules per mole (kJ/mol) to joules per molecule. Use Avogadro's number \( 6.022 \times 10^{23} \text{ mol}^{-1} \) for this conversion.
Use the energy-wavelength relationship given by the equation \( E = \frac{hc}{\lambda} \), where \( E \) is the energy per photon, \( h \) is Planck's constant \( 6.626 \times 10^{-34} \text{ J s} \), and \( c \) is the speed of light \( 3.00 \times 10^8 \text{ m/s} \).
Rearrange the equation to solve for wavelength \( \lambda \): \( \lambda = \frac{hc}{E} \). Substitute the values for \( h \), \( c \), and \( E \) to find the wavelength required for the dissociation.

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Key Concepts

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

Photodissociation

Photodissociation is a process in which a chemical compound breaks down into its components upon absorbing light. In the case of water vapor (H2O), it can dissociate into hydrogen (H) and hydroxyl radicals (OH) when exposed to ultraviolet (UV) radiation. Understanding this concept is crucial for analyzing how light interacts with molecules in the atmosphere and the resulting chemical reactions.

Wavelength and Energy Relationship

The energy of a photon is inversely related to its wavelength, described by the equation E = hc/λ, where E is energy, h is Planck's constant, c is the speed of light, and λ is the wavelength. This relationship is essential for calculating the wavelength required to provide enough energy to break chemical bonds during photodissociation. Knowing how to manipulate this equation allows for the determination of the specific wavelength needed for a given reaction.
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Parts Per Million (ppm)

Parts per million (ppm) is a unit of measurement used to describe the concentration of a substance in a solution or mixture. In the context of atmospheric chemistry, a concentration of 5 ppm indicates that there are 5 molecules of H2O for every million molecules of air. This concept is important for understanding the relative abundance of water vapor in the stratosphere and its potential impact on photodissociation processes.
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Related Practice
Textbook Question

In 1986 an electrical power plant in Taylorsville, Georgia, burned 8,376,726 tons of coal, a national record at that time. (b) If 55% of the SO2 could be removed by reaction with powdered CaO to form CaSO3, how many tons of CaSO3 would be produced?

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Textbook Question

The concentration of H2O in the stratosphere is about 5 ppm. It undergoes photodissociation according to: H2O(g) → H(g) + OH(g)

(c) The hydroxyl radical, OH, can react with ozone, giving the following reactions:

OH(g) + O3(g) → HO2(g) + O2(g)

HO2(g) + O(g) → OH(g) + O2(g)

What overall reaction results from these two elementary reactions? What is the catalyst in the overall reaction? Explain.

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Textbook Question

In 1986 an electrical power plant in Taylorsville, Georgia, burned 8,376,726 tons of coal, a national record at that time. (a) Assuming that the coal was 83% carbon and 2.5% sulfur and that combustion was complete, calculate the number of tons of carbon dioxide and sulfur dioxide produced by the plant during the year.

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Textbook Question

The water supply for a midwestern city contains the following impurities: coarse sand, finely divided particulates, nitrate ions, trihalomethanes, dissolved phosphorus in the form of phosphates, potentially harmful bacterial strains, dissolved organic substances. Which of the following processes or agents, if any, is effective in removing each of these impurities: coarse sand filtration, activated carbon filtration, aeration, ozonization, precipitation with aluminum hydroxide?

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