Solved: The average bond enthalpies of the CCl and CF

Describe the regions of Earth’s atmosphere

Briefly outline the main processes of the nitrogen and oxygen cycles

Explain why, for maximum performance, supersonic airplanes need to fly at a high altitude (in the stratosphere)

Jupiters atmosphere consists mainly of hydrogen (90 percent) and helium (9 percent). How does this mixture of gases contrast with the composition of Earths atmosphere? Why does the composition differ?

Referring to Table 20.1, calculate the mole fraction of CO2 and its concentration in parts per million by volume.

Calculate the partial pressure of CO2 (in atm) in dry air when the atmospheric pressure is 754 mmHg.

Describe the processes that result in the warming of the stratosphere.

Calculate the total mass (in kilograms) of nitrogen, oxygen, and carbon dioxide gases in the atmosphere. (Hint: See Problem 5.106 and Table 20.1. Use 29.0 g/mol for the molar mass of ai

What process gives rise to aurora borealis and aurora australis?

Why can astronauts not release oxygen atoms to test the mechanism of shuttle glow?

The highly reactive OH radical (a species with an unpaired electron) is believed to be involved in some atmospheric processes. Table 9.4 lists the bond enthalpy for the oxygen-to-hydrogen bond in OH as 460 kJ/mol. What is the longest wavelength (in nm) of radiation that can bring about the reaction OH(g) O(g) 1 H(g)

The green color observed in aurora borealis is produced by the emission of a photon by an electronically excited oxygen atom at 558 nm. Calculate the energy difference between the two levels involved in the emission process.

Briefly describe the absorption of solar radiation in the stratosphere by O2 and O3 molecules.

Explain the processes that have a warming effect on the stratosphere.

List the properties of CFCs, and name four major uses of these compounds

How do CFCs and nitrogen oxides destroy ozone in the stratosphere?

What causes the polar ozone holes?

How do volcanic eruptions contribute to ozone destruction?

Describe ways to curb the destruction of ozone in the stratosphere

Discuss the effectiveness of some of the CFC substitutes.

Given that the quantity of ozone in the stratosphere is equivalent to a 3.0-mm-thick layer of ozone on Earth at STP, calculate the number of ozone molecules in the stratosphere and their mass in kilograms. (Hint: The radius of Earth is 6371 km and the surface area of a sphere is 4r 2 , where r is the radius.)

Referring to the answer in Problem 20.21, and assuming that the level of ozone in the stratosphere has already fallen 6.0 percent, calculate the number of kilograms of ozone that would have to be manufactured on a daily basis so that we could restore the ozone to the original level in 100 yr. If ozone is made according to the process 3O2(g) 2O3(g), how many kilojoules of energy would be required?

Both Freon-11 and Freon-12 are made by the reaction of carbon tetrachloride (CCl4) with hydrogen fluoride. Write equations for these reactions

Why are CFCs not decomposed by UV radiation in the troposphere?

The average bond enthalpies of the CCl and CF bonds are 340 kJ/mol and 485 kJ/mol, respectively. Based on this information, explain why the CCl bond in a CFC molecule is preferentially broken by solar radiation at 250 nm

Like CFCs, certain bromine-containing compounds such as CF3Br can also participate in the destruction of ozone by a similar mechanism starting with the Br atom: CF3Br CF3 1 Br Given that the average CBr bond enthalpy is 276 kJ/mol, estimate the longest wavelength required to break this bond. Will this compound be decomposed in the troposphere only or in both the troposphere and stratosphere?

Draw Lewis structures for chlorine nitrate (ClONO2) and chlorine monoxide (ClO).

Draw Lewis structures for HCFC-123 (CF3CHCl2) and CF3CFH2.

What are the effects of volcanic eruptions on climate?

Classify the reaction between H2S and SO2 that leads to the formation of sulfur at the site of a volcanic eruption.

What is the greenhouse effect? What is the criterion for classifying a gas as a greenhouse gas?

Why is more emphasis placed on the role of carbon dioxide in the greenhouse effect than on that of water?

Describe three human activities that generate carbon dioxide. List two major mechanisms for the uptake of carbon dioxide

Deforestation contributes to the greenhouse effect in two ways. What are they?

How does an increase in world population enhance the greenhouse effect?

Is ozone a greenhouse gas? If so, sketch three ways an ozone molecule can vibrate

What effects do CFCs and their substitutes have on Earths temperature?

Why are CFCs more effective greenhouse gases than methane and carbon dioxide?

The annual production of zinc sulfide (ZnS) is 4.0 3 104 tons. Estimate the number of tons of SO2 produced by roasting it to extract zinc metal.

Calcium oxide or quicklime (CaO) is used in steelmaking, cement manufacture, and pollution control. It is prepared by the thermal decomposition of calcium carbonate: CaCO3(s) CaO(s) 1 CO2(g) Calculate the yearly release of CO2 (in kilograms) to the atmosphere if the annual production of CaO in the United States is 1.7 3 1010 kg.

The molar heat capacity of a diatomic molecule is 29.1 J/K ? mol. Assuming the atmosphere contains only nitrogen gas and there is no heat loss, calculate the total heat intake (in kilojoules) if the atmosphere warms up by 3C during the next 50 yr. Given that there are 1.8 3 1020 moles of diatomic mol ecules present, how many kilograms of ice (at the North and South Poles) will this quantity of heat melt at 0C? (The molar heat of fusion of ice is 6.01 kJ/mol.)

As mentioned in the chapter, spraying the stratosphere with hydrocarbons such as ethane and propane should eliminate Cl atoms. What is the drawback of this procedure if used on a large scale for an extended period of time?

Name the gas that is largely responsible for the acid rain phenomenon.

List three detrimental effects of acid rain

Briefly discuss two industrial processes that lead to acid rain

Discuss ways to curb acid rain.

Water and sulfur dioxide are both polar molecules and their geometry is similar. Why is SO2 not considered a major greenhouse gas?

Describe the removal of SO2 by CaO (to form CaSO3) in terms of a Lewis acid-base reaction.

An electric power station annually burns 3.1 3 107 kg of coal containing 2.4 percent sulfur by mass. Calculate the volume of SO2 emitted at STP

The concentration of SO2 in the troposphere over a certain region is 0.16 ppm by volume. The gas dissolves in rainwater as follows: SO2(g) 1 H2O(l) H1(aq) 1 HSO3 2(aq) Given that the equilibrium constant for the preceding reaction is 1.3 3 1022 , calculate the pH of the rainwater. Assume that the reaction does not affect the partial pressure of SO2.

What is photochemical smog? List the factors that favor the formation of photochemical smog.

What are primary and secondary pollutants?

Identify the gas that is responsible for the brown color of photochemical smog.

The safety limits of ozone and carbon monoxide are 120 ppb by volume and 9 ppm by volume, respectively. Why does ozone have a lower limit?

Suggest ways to minimize the formation of photochemical smog.

In which region of the atmosphere is ozone beneficial? In which region is it detrimental?

Assume that the formation of nitrogen dioxide: 2NO(g) 1 O2(g) 2NO2(g) is an elementary reaction. (a) Write the rate law for this reaction. (b) A sample of air at a certain temperature is contaminated with 2.0 ppm of NO by volume. Under these conditions, can the rate law be simplified? If so, write the simplified rate law. (c) Under the conditions described in (b), the halflife of the reaction has been estimated to be 6.4 3 103 min. What would the half-life be if the initial concentration of NO were 10 ppm?

The gas-phase decomposition of peroxyacetyl nitrate (PAN) obeys first-order kinetics: CH3COOONO2 CH3COOO 1 NO2 with a rate constant of 4.9 3 1024 s21 . Calculate the rate of decomposition in M/s if the concentration of PAN is 0.55 ppm by volume. Assume STP conditions

On a smoggy day in a certain city the ozone concentration was 0.42 ppm by volume. Calculate the partial pressure of ozone (in atm) and the number of ozone molecules per liter of air if the temperature and pressure were 20.0C and 748 mmHg, respectively

Which of the following settings is the most suitable for photochemical smog formation? (a) Gobi desert at noon in June, (b) New York City at 1 p.m. in July, (c) Boston at noon in January. Explain your choice.

List the major indoor pollutants and their sources.

What is the best way to deal with indoor pollution?

Why is it dangerous to idle a cars engine in a poorly ventilated place, such as the garage?

Describe the properties that make radon an indoor pollutant. Would radon be more hazardous if 222Rn had a longer half-life?

A concentration of 8.00 3 102 ppm by volume of CO is considered lethal to humans. Calculate the minimum mass of CO in grams that would become a lethal concentration in a closed room 17.6 m long, 8.80 m wide, and 2.64 m high. The temperature and pressure are 20.0C and 756 mmHg, respectively.

A volume of 5.0 L of polluted air at 18.0C and 747 mmHg is passed through lime water [an aqueous suspension of Ca(OH)2], so that all the carbon dioxide present is precipitated as CaCO3. If the mass of the CaCO3 precipitate is 0.026 g, calculate the percentage by volume of CO2 in the air sample.

Briefly describe the harmful effects of the following substances: O3, SO2, NO2, CO, CH3COOONO2 (PAN), Rn.

The equilibrium constant (KP) for the reaction N2(g) 1 O2(g) 2NO(g) is 4.0 3 10231 at 25C and 2.6 3 1026 at 1100C, the temperature of a running cars engine. Is this an endothermic or exothermic reaction?

As stated in the chapter, carbon monoxide has a much higher affinity for hemoglobin than oxygen does. (a) Write the equilibrium constant expression (Kc) for the following process: CO(g) 1 HbO2(aq) O2(g) 1 HbCO(aq) where HbO2 and HbCO are oxygenated hemoglobin and carboxyhemoglobin, respectively. (b) The composition of a breath of air inhaled by a person smoking a cigarette is 1.9 3 1026 mol/L CO and 8.6 3 1023 mol/L O2. Calculate the ratio of [HbCO] to [HbO2], given that Kc is 212 at 37C.

Instead of monitoring carbon dioxide, suggest another gas that scientists could study to substantiate the fact that CO2 concentration is steadily increasing in the atmosphere.

In 1991 it was discovered that nitrous oxide (N2O) is produced in the synthesis of nylon. This compound, which is released into the atmosphere, contributes both to the depletion of ozone in the stratosphere and to the greenhouse effect. (a) Write equations representing the reactions between N2O and oxygen atoms in the stratosphere to produce nitric oxide (NO), which is then oxidized by ozone to form nitrogen dioxide. (b) Is N2O a more effective greenhouse gas than carbon dioxide? Explain. (c) One of the intermediates in nylon manufacture is adipic acid [HOOC(CH2)4COOH]. About 2.2 3 109 kg of adipic acid are consumed every year. It is estimated that for every mole of adipic acid produced, 1 mole of N2O is generated. What is the maximum number of moles of O3 that can be destroyed as a result of this process per year?

A glass of water initially at pH 7.0 is exposed to dry air at sea level at 20C. Calculate the pH of the water when equilibrium is reached between atmospheric CO2 and CO2 dissolved in the water, given that Henrys law constant for CO2 at 20C is 0.032 mol/L ? atm. (Hint: Assume no loss of water due to evaporation and use Table 20.1 to calculate the partial pressure of CO2. Your answer should correspond roughly to the pH of rainwater.)

A 14-m by 10-m by 3.0-m basement had a high radon content. On the day the basement was sealed off from its surroundings so that no exchange of air could take place, the partial pressure of 222Rn was 1.2 3 1026 mmHg. Calculate the number of 222Rn isotopes (t1 2 5 3.8 d) at the beginning and end of 31 days. Assume STP conditions.

Ozone in the troposphere is formed by the following steps: NO2 NO 1 O (1) O 1 O2 O3 (2) The first step is initiated by the absorption of visible light (NO2 is a brown gas). Calculate the longest wavelength required for step (1) at 25C. [Hint: You need to first calculate DH and hence DU for (1). Next, determine the wavelength for decomposing NO2 from DU.]

Although the hydroxyl radical (OH) is present only in a trace amount in the troposphere, it plays a central role in its chemistry because it is a strong oxidizing agent and can react with many pollutants as well as some CFC substitutes (see p. 910). The hydroxyl radical is formed by the following reactions: O3 , 320 nm O* 1 O2 O 1 H2O 2OH where O* denotes an electronically excited atom. (a) Explain why the concentration of OH is so small even though the concentrations of O3 and H2O are quite large in the troposphere. (b) What property makes OH a strong oxidizing agent? (c) The reaction between OH and NO2 contributes to acid rain. Write an equation for this process. (d) The hydroxyl radical can oxidize SO2 to H2SO4. The first step is the formation of a neutral HSO3 species, followed by its reaction with O2 and H2O to form H2SO4 and the hydroperoxyl radical (HO2). Write equations for these processes.

The equilibrium constant (KP) for the reaction 2CO(g) 1 O2(g) 2CO2(g) is 1.4 3 1090 at 25C. Given this enormous value, why doesnt CO convert totally to CO2 in the troposphere?

A person was found dead of carbon monoxide poisoning in a well-insulated cabin. Investigation showed that he had used a blackened bucket to heat water on a butane burner. The burner was found to function properly with no leakage. Explain, with an appropriate equation, the cause of his death

The carbon dioxide level in the atmosphere today is often compared with that in preindustrial days. Explain how scientists use tree rings and air trapped in polar ice to arrive at the comparison.

What is funny about the following cartoon?

Calculate the standard enthalpy of formation (DHf) of ClO from the following bond enthalpies: Cl2: 242.7 kJ/mol; O2: 498.7 kJ/mol; ClO: 206 kJ/mol.

Methyl bromide (CH3Br, b.pt. 3.6C) is used as a soil fumigant to control insects and weeds. It is also a marine by-product. Photodissociation of the CBr bond produces Br atoms that can react with ozone similar to Cl, except more effectively. Do you expect CH3Br to be photolyzed in the troposphere? The bond enthalpy of the CBr bond is about 293 kJ/mol.

The effective incoming solar radiation per unit area on Earth is 342 W/m2 . Of this radiation, 6.7 W/m2 is absorbed by CO2 at 14,993 nm in the atmosphere. How many photons at this wavelength are absorbed per second in 1 m2 by CO2? (1 W 5 1 J/s)

As stated in the chapter, about 50 million tons of sulfur dioxide are released into the atmosphere every year. (a) If 20 percent of the SO2 is eventually converted to H2SO4, calculate the number of 1000-lb marble statues the resulting acid rain can damage. As an estimate, assume that the acid rain only destroys the surface layer of each statue, which is made up of 5 percent of its total mass. (b) What is the other undesirable result of the acid rain damage?

Peroxyacetyl nitrate (PAN) undergoes thermal decomposition as follows: CH3(CO)OONO2 CH3(CO)OO 1 NO2 The rate constant is 3.0 3 1024 s21 at 25C. At the boundary between the troposphere and stratosphere, where the temperature is about 240C, the rate constant is reduced to 2.6 3 1027 s21 . (a) Calculate the activation energy for the decomposition of PAN. (b) What is the half-life of the reaction (in minutes) at 25C?

How are past temperatures determined from ice cores obtained from the Artic or Antarctica? (Hint: Look up the stable isotopes of hydrogen and oxygen. How does energy required for vaporization depend on the masses of H2O molecules containing different isotopes? How would you determine the age of an ice core?)

The balance between SO2 and SO3 is important in understanding acid rain formation in the troposphere. From the following information at 25C S(s) 1 O2(g) SO2(g) K1 5 4.2 3 1052 2S(s) 1 3O2(g) 2SO3(g) K2 5 9.8 3 10128 calculate the equilibrium constant for the reaction 2SO2(g) 1 O2(g) 2SO3(g)

Draw Lewis structures of the species in each step in the conversion of SO2 to H2SO4 discussed on p. 917.

The HO3 radical was once thought of as a temporary reservoir of atmospheric OH radicals. Draw a Lewis structure of the species.

What is the difference between weather and climate? In the winter months of 2010, record snows fell on the East Coast from Washington, D.C., to the Deep South. Can this occurrence be taken as evidence against global warming? Can you suggest one way in which global warming might actually be responsible for what happened?

Estimate the annual production of carbon dioxide (in kilograms) by an average passenger car in the United States.

The following reactions are common in the stratosphere: (a) NO2(g) NO(g) 1 O(g) (b) N2O(g) N2(g) 1 O(g) (c) H2(g) 1 O(g) OH(g) 1 H(g) (d) CH4(g) 1 O(g) OH(g) 1 CH3(g) First, without doing any calculations, predict whether each of the reactions is endothermic or exothermic. Then estimate DH for each reaction, and comment on your predictions and estimates.