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Ch.18 - Chemistry of the Environment
All textbooksBrown 14th EditionCh.18 - Chemistry of the EnvironmentProblem 84
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Chapter 18, Problem 84

The standard enthalpies of formation of ClO and ClO2 are 101 and 102 kJ/mol, respectively. Using these data and the thermodynamic data in Appendix C, calculate the overall enthalpy change for each step in the following catalytic cycle: ClO(g) + O(g) → ClO(g) + O(g). What is the enthalpy change for the overall reaction that results from these two steps?

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Step 1: Identify the given data and the reaction. The problem provides the standard enthalpies of formation for ClO and ClO2 as 101 kJ/mol and 102 kJ/mol, respectively. The reaction given is ClO(g) + O(g) → ClO(g) + O(g).
Step 2: Recognize that the reaction provided is a balanced equation where the reactants and products are the same, indicating no net change in the chemical species involved.
Step 3: Understand that since the reactants and products are identical, the enthalpy change for this reaction is zero. This is because the enthalpy of formation of the reactants is equal to the enthalpy of formation of the products.
Step 4: Consider the concept of Hess's Law, which states that the total enthalpy change for a reaction is the same, no matter how many steps the reaction is carried out in. Since the reaction does not change the chemical species, the enthalpy change remains zero.
Step 5: Conclude that the enthalpy change for the overall reaction, given the identical reactants and products, is zero. This is consistent with the principle that no net chemical change results in no enthalpy change.
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Textbook Question

An impurity in water has an extinction coefficient of 3.45⨉103 M-1 cm-1 at 280 nm, its absorption maximum (A Closer Look, p. 576). Below 50 ppb, the impurity is not a problem for human health. Given that most spectrometers cannot detect absorbances less than 0.0001 with good reliability, is measuring the absorbance of a water sample at 280 nm a good way to detect concentrations of the impurity above the 50-ppb threshold?

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Textbook Question

The concentration of H2O in the stratosphere is about 5 ppm. It undergoes photodissociation according to: H2O1g2 ¡ H1g2 + OH1g2 (b) Using Table 8.3, calculate the wavelength required to cause this dissociation.

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Open Question
Bioremediation is the process by which bacteria repair their environment in response, for example, to an oil spill. The efficiency of bacteria for 'eating' hydrocarbons depends on the amount of oxygen in the system, pH, temperature, and many other factors. In a certain oil spill, hydrocarbons from the oil disappeared with a first-order rate constant of 2 * 10 s. At that rate, how many days would it take for the hydrocarbons to decrease to 10% of their initial value?
Open Question
The main reason that distillation is a costly method for purifying water is the high energy required to heat and vaporize water. (a) Using the density, specific heat, and heat of vaporization of water from Appendix B, calculate the amount of energy required to vaporize 1.00 gal of water beginning with water at 20 °C. (b) If the energy is provided by electricity costing $0.085/kWh, calculate its cost. (c) If distilled water sells in a grocery store for $1.26 per gal, what percentage of the sales price is represented by the cost of the energy?
Open Question
A reaction that contributes to the depletion of ozone in the stratosphere is the direct reaction of oxygen atoms with ozone: O(g) + O3(g) → 2 O2(g). At 298 K, the rate constant for this reaction is 4.8 × 10⁵ M⁻¹ s⁻¹. Would you expect this reaction to occur via a single elementary process? Explain why or why not.
Textbook Question

The following data were collected for the desturction of O3 by H (O3 + H → O2 + OH) at very low concentrations (b) Calculate the rate constant

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