1. a. List three fossil fuels.
b. What is the origin of fossil fuels?
c. Are fossil fuels a renewable resource?
2. The Calorie, used to express food heat values, is the same as a kilocalorie of heat energy. If you eat a chocolate bar from the United States with 600 Calories of food energy, how does the energy compare with eating a Swiss chocolate bar that has 3000 kJ of food energy? (Note: 1 kcal = 4.184 kJ)
3. A single serving bag of Granny Goose Hawaiian Style Potato Chips has 70 Cal. Assuming that all of the energy from eating these chips goes toward keeping your heart beating, how long can these chips sustain a heartbeat of 80 beats per minute? Note: 1 kcal = 4.184 kJ, and each human heart beat requires approximately 1 J of energy.
4. Three power plants have been proposed that operate at these efficiencies.
| Plant | Power Plant Efficiency (%) |
| I | 81 |
| II | 66 |
| III | 41 |
a. Calculate the overall efficiency of each plant (not the maximum theoretical efficiency) using the other efficiencies given in Table 4.1.
b. Identify the factors that affect the efficiency.
c. Discuss the practical limits that govern such efficiencies. Which plant would be most likely to be built? If plant III only costs half of plant I or II to operate, which would be most likely to be built?
5. Equation 4.1 shows the complete combustion of methane.
a. By analogy, write a similar chemical equation using ethane, C2H6.
b. Represent this equation with Lewis structures.
6. The heat of combustion for ethane, C2H6, is 52.0 kJ/g. How much heat would be released if
1 mol of ethane undergoes complete combustion?
7. a. Write the chemical equation for the complete combustion of heptane, C7H16.
b. The heat of combustion for heptane is 4817 kJ/mol. How much heat would be released if 250 kg of heptane undergoes complete combustion?
10. From personal experience, state whether these processes are endothermic or exothermic. Give a reason for each.
a. A charcoal briquette burns.
b. Water evaporates from your skin.
c. Ice melts.
d. Wood burns.
11. Use the bond energies in Table 4.2 to explain why:
a. chlorofluorocarbons, CFCs, are so stable.
b. it takes less energy to release Cl atoms than F atoms from CFCs.
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12. Use the bond energies in Table 4.2 to calculate the energy changes associated with each of these reactions. Lewis structures of the reactants and products may be useful for determining the number and kinds of bonds. Label each reaction as endothermic or exothermic.
a. N2(g) + 3 H2(g) ¾® 2 NH3(g)
b. 2 C5H12(g) + 11 O2(g) ¾® 10 CO(g) + 12 H2O(l)
c. H2(g) + Cl2(g) ¾® 2 HCl(g)
13. Use the bond energies in Table 4.2 to calculate the energy changes associated with each of these reactions. Label each reaction as endothermic or exothermic.
a. 2 H2(g) + CO(g) ¾® CH3OH(g)
b. H2(g) + O2(g) ¾® H2O(g)
c. 2 BrCl(g) ¾® Br2(g) + Cl2(g)
14. Use Figure 4.9 to compare the sources of U.S. energy consumption. Arrange the sources in order of decreasing percentage and comment on the relative rankings.
15. Table 4.3 lists the energy content of some fuels in kilojoules per gram (kJ/g). Calculate the fuel energy in kilojoules per mole (kJ/mol) for methane CH4, propane C3H8, hydrogen H2, coal, and ethanol C2H6O. Make a generalization regarding the chemical composition of fuels and their respective energy contents. Visit Figures Alive! at the Online Learning Center for related activities.
16. Mercury is present in minor amounts (50–200 ppb) in coal. Use the amount of coal burned by a power plant in Your Turn 4.12 to determine how much Hg is released by that plant. Calculate the amount based on the lower (50 ppb) and higher (200 ppb) limits.
17. An energy consumption of 650,000 kcal per person per day is equivalent to an annual personal consumption of 65 barrels of oil or 16 tons of coal. Use this information to calculate the amount of energy available in each of these quantities.
a. one barrel of oil
b. 1 gal of oil (42 gal per barrel)
c. one ton of coal
d. a lb of coal (2000 lb per ton)
18. Use the information in question 17 to find the ratio of the quantity of energy available in 1 lb of coal to that in 1 lb of oil. Hint: One pound of oil has a volume of 0.56 qt.
19. Consider the data for three hydrocarbons shown in the table.
| Compound, formula | Melting Point (°C) | Boiling Point (°C) |
| Pentane, C5H12 | -130 | 36 |
| Triacontane, C30H62 | 66 | 450 |
| Octane, C8H18 | -57 | 125 |
Predict the physical state (solid, liquid, or gas) of each hydrocarbon at a temperature of
25 °C.
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20. Table 4.5 shows the structural formulas of alkanes containing one to eight carbons.
a. Draw the structural formula for decane, C10H22.
b. Use Table 4.5 to predict the structural formulas for nonane, the alkane with 9 carbons, and dodecane, the alkane with 12 carbons.
c. The structural formulas in Table 4.5 are two-dimensional. Use the bond angle information in Chapter 3 to predict the C-to-C-to-C and H-to-C-to-H bond angles in decane.
22. This is the ball-and-stick representation of one isomer of butane (C4H10).
a. Draw the Lewis structure for this isomer. Hint: Show how atoms are linked, but not their spatial arrangement.
b. Draw the Lewis structure for each additional isomer, being careful not to repeat isomers.
c. What is the total number of isomers of C4H10?
23. A premium gasoline available at most stations has an octane rating of 92. What does that tell you about:
a. the knocking characteristics of this gasoline?
b. whether the fuel contains oxygenates?
24. How might you explain the difference between temperature and heat to a friend? Use some practical, everyday examples.
25. Write a response to this statement: "Because of the first law of thermodynamics, there can never be an energy crisis."
26. Candle wax, a hydrocarbon, is composed of straight-chain hydrocarbons with about 50 carbon atoms.
a. Make a general statement describing how the number of carbon atoms affects the physical state of normal hydrocarbons.
b. Write a chemical formula for the alkane having 50 carbon atoms.
27. A friend tells you that hydrocarbons containing larger molecules are better fuels than those containing smaller ones.
a. Use these data, together with appropriate calculations, to discuss the merits of this statement.
| Hydrocarbon | Heat of Combustion |
| Octane, C8H18 | 5450 kJ/mol |
| Butane, C4H10 | 2859 kJ/mol |
b. Considering your answer to part a, do you expect the heat of combustion per gram of candle wax, C25H52, to be more or less than the heat of combustion per gram of octane? Do you expect the molar heat of combustion of candle wax to be more or less than the molar heat of combustion of octane? Justify your predictions.
28. Halons are synthetic chemicals similar to CFCs, but they also include bromine. Although halons are excellent materials for fire fighting, they more effectively deplete ozone than CFCs. Here is the Lewis structure for halon-1211.
a. Which bond in this compound is broken most easily? How is that related to the ability of this compound to interact with ozone?
b. C2HClF4 is a compound being considered as a replacement for halons as a fire extinguisher. Draw the Lewis structure for this compound and identify the bond broken most easily. How is the structure related to the ability of this compound to interact with ozone?
29. The Fischer–Tropsch conversion of hydrogen and carbon monoxide into hydrocarbons and water was given in Equation 4.12:
n CO + (2n + 1) H2 ¾® CnH2n + 2 + n H2O
a. Determine the heat evolved by this reaction when n = 1.
b. Without doing a calculation, do you think that more or less energy will be given off in the formation of larger hydrocarbons (n > 1)? Explain your reasoning.
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30. During the distillation of petroleum, kerosene and hydrocarbons with 12–18 carbons used for diesel fuel will condense at position C marked on this diagram.
a. Separating hydrocarbons by distillation depends on differences in a specific physical property. Which one?
b. How will the number of carbon atoms in the hydrocarbon molecules separated at A, B, and D compare with those separated at position C? Explain your prediction.
c. How will the uses of the hydrocarbons separated at A, B, and D differ from those separated at position C? Explain your reasoning.
31. Imagine you are at the molecular level, looking at what happens when liquid ethylene, C2H4, boils. Consider a collection of four ethylene molecules.
a. Draw a representation of ethylene in the liquid state and then in the gaseous state. How will the two differ?
b. Estimate the temperature at which the transition from liquid to gas is taking place. What is the basis for your estimation?
32. Explain why cracking is necessary in the refinement of crude oil.
33. Catalysts speed up cracking reactions in oil refining and allow them to be carried out at lower temperatures. What other examples of catalysts were given in the first three chapters of this text?
34. Octane ratings of several substances are listed in Table 4.6.
a. What evidence can you give that the octane rating is or is not a measure of the energy content of a gasoline?
b. Octane ratings are measures of a fuel's ability to minimize or prevent engine knocking. Why is the prevention of knocking important?
c. Why are higher octane rating gasolines more expensive than lower ones?
35. The octane rating describes a fuel's resistance to preignition. Considering Figure 4.19, how do the activation energies for combustion of n-octane and isooctane compare? Explain.
36. The combustion of ethanol produces about 40% less energy per gram than normal hydrocarbon fuels. In 2006, the Indy car racing circuit will begin to use engines that have been modified to run on pure ethanol, replacing the current engines that run on methanol, CH3OH. Why do you think these high-performance vehicles are switching to ethanol?
37. One risk of depending on foreign oil is periodic gasoline shortages due to unfavorable international events. Does a gasoline shortage affect only individual motorists? Name some ways that a gasoline shortage could affect your life.
38. These three structures have the chemical formula C8H18. The hydrogen atoms and C-to-H bonds have been omitted for simplicity.
a. Fill in the missing hydrogen atoms and C-to-H bonds and confirm that these structures all represent C8H18.
b. Are any of these representations identical isomers? If so, which ones?
c. Obtain a model kit and construct one of the structures. What are the C-to-C-to-C bond angles?
d. If you were to build a different one, would the C-to-C-to-C bond angles change? Explain?
e. Draw the structural formula of two more isomers of C8H18.
39. A ball-and-stick model of ethanol, C2H6O, is shown here. Dimethyl ether also has the formula C2H6O. Rearrange the atoms in ethanol to draw the Lewis structure of dimethyl ether. Hint: Remember to complete the octet for the carbon and oxygen atoms.
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40. How is the growth in oxygenated gasolines related to:
a. restrictions on the use of lead in gasoline?
b. federal and state air quality regulations?
41. Do oxygenated fuels have a higher energy content than nonoxygenated fuels? Use the bond energies in Table 4.2 to calculate the heat of combustion of MTBE.
42. Your neighbor is shopping for a new family vehicle. The salesperson identified a van to be of interest as a flexible fuel vehicle (FFV).
a. Explain what is meant by FFV to your neighbor.
b. What does it mean for the van to be able to use E85 fuel?
c. Would your neighbor and his family be particularly interested in using E85 fuel depending on what region of the country they live?
43. Find information about the availability of biodiesel fuel distributors in the United States.
a. Why are a majority of the distributors located where they are?
b. According the National Biodiesel Board, their distributors will ship the fuel anywhere in the country, particularly to operators of fleets of trucks or cars. Would trucking companies in Florida and Oklahoma both be equally interested? List factors that would be important in such a decision.
44. China's large population has increased energy consumption as the standard of living increases.
a. Report on China's increasing number of automobiles over the last 10 years.
b. What evidence suggests that the increase in the number of vehicles has affected air quality? What interventions, if any, does the Chinese government have underway?
45. The concept of entropy and disorder is used in games like poker. Describe how the rank of hands (from a simple high card to a royal flush) is related to entropy.
46. Another claim in the Scientific American article by Lovins referenced in Section 4.11 was that replacing an incandescent bulb (75 W) with a compact fluorescent bulb (18 W) would save about 75% in the cost of electricity. Electricity is generally priced per kilowatt-hour (kwh). Using the price of electricity where you live, calculate how much money you would save over the life of one compact fluorescent bulb (about 10,000 hr).
47. Section 4.9 states that RFGs burn more cleanly by producing less carbon monoxide than nonoxygenated fuels. What evidence supports this statement?
48. Another type of catalyst used in the combustion of fossil fuels is the catalytic converter that was discussed in Chapter 1. One of the reactions that these catalysts speed up is the conversion of NO(g) to N2(g) and O2(g).
a. Draw a diagram of the energy of this reaction similar to the one shown in Figure 4.19.
b. Why is this such an important reaction? Hint: See Sections 1.9 and 1.11.
49. Chemical explosions are very exothermic reactions. Describe the relative bond strengths in the reactants and products that would make for a good explosion.
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51. You may have seen some General Motors advertisements using the slogan "Live Green by Going Yellow" for their FlexFuel vehicles that can use E85 gasoline. To what do the colors in this slogan refer?
52. Explain why a distillation tower can separate a mixture of hydrocarbons into different fractions, but it is not possible to separate seawater, also a complex mixture, into all of its different fractions in the same manner.
53. Section 4.8 states that both n-octane and isooctane have essentially the same heat of combustion. How is that possible if they have different structures? Explain.
54. Why do you think that countries are willing to go to war over energy issues, but not over other environmental issues? Write a brief op-ed piece for your school newspaper discussing this issue.
55. Since the inception of reformulated gasoline requirements, MTBE has been preferred over ethanol by oil companies. One reason for this is the infrastructure requirements. MTBE can be blended with gasoline at the refinery, whereas ethanol must be shipped separately and mixed with the fuel at the filling station. Why the difference? Hint: A detailed look at solubility will be given in the next chapter.
56. What relative advantages and disadvantages are associated with using coal and with using oil as energy sources? Which do you see as the better fuel for the 21st century? Give reasons for your choice.
57. What are the advantages and disadvantages of replacing gasoline with renewable fuels such as ethanol? Indicate your personal position on the issue and state your reasoning.
58. According to the EPA, driving a car is "a typical citizen's most 'polluting' daily activity."
a. Do you agree? Why or why not?
b. What pollutants do cars emit?
Hint: Information on automobile emissions provided by the EPA (together with the information in this text) can help you fully answer this question.
c. RFGs play a role in reducing emissions. Where in the country are RFGs required? Check the current list published on the Web by the EPA.
d. Explain which emissions RFGs are supposed to lower.
59. It was stated in Section 4.11 that the Three Gorges Dam in China is a controversial project. Use the resources of the Web to investigate some of the major issues concerning this dam.
60. C. P. Snow, a noted scientist and author, wrote an influential book called The Two Cultures, in which he stated: "The question, 'Do you know the second law of thermodynamics?' is the cultural equivalent of 'Have you read a work of Shakespeare's?'" How do you react to this comparison? Discuss these questions in light of your own educational experiences.
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