ANSWERS TO END-OF-CHAPTER QUESTIONS SECTION F PAGE 27

CHAPTER 4: ENERGY, CHEMISTRY, AND SOCIETY

Emphasizing Essentials 1. a. Examples are coal, oil, and natural gas.

b. Fossil fuels originated as plant or animal matter 150-300 million years ago. c. No, they are not. The time scale of their formation means they are not renewable in the short term.

2. The temperature, 70°C, is the same in each container. The heat content of the water is not the same. Heat depends on both the temperature and the size of the sample. There is twice the heat in the water in Container 1 compared with the water in Container 2 because there is twice the mass of water present in Container 1.

3. 600 kcal !4.184 kJ

1 kcal= 2510 kJ ; This means the Swiss chocolate bar, with 3000 kJ, has more food energy.

4. 70 kcal !4.184 kJ

1 kcal!

1000 J

1 kJ= 2.9 !10

5kJ of energy from the single serving bag of chips

2.9! 105

J !1minute

80 J= 3.6 ! 10

3min , or about 60 hours from this bag of chips

5. a. Overall efficiency: Plant 1: 43.6%; Plant II: 35.6%; Plant III: 22.1%. b. The efficiency of the burner increases as the difference between the two operating temperatures

increases. c. Plant II is most likely to be built. The high temperature for plant I might be difficult to achieve. The low

temperature for plant III could not be achieved on Earth without extensive refrigeration. 6. The plate of spaghetti has a higher state of entropy assuming the noodles are strewn about the plate

randomly. The cards in the deck are held tightly together in a ridged, orderly stack. 7. a. 2 C2H6 � + 7 O2 → 4 CO2 � + 6 H2O b.

C C

H

H

H

H

H

H

O O C OO O

H H

4 672 + +

c.

8.

52.0 kJ

1 g C 2H6!

30.1 g C 2H6

1 mol C2H6 =

1560 kJ

mol C2H 6

9. a. C7H16 + 11 O2 → 7 CO2 + 8 H2O

CHAPTER 4: ENERGY, CHEMISTRY, AND SOCIETY

SECTION F PAGE 28 ANSWERS TO END-OF-CHAPTER QUESTIONS

b. 167

7

167167

167

167

1673

167HC mole

kJ102.1

HC mole1

kJ4817

HC g 2.001

HC mole1

HC kg

HC g10HCkg250

!=!!!

10. Note that in an endothermic reaction, the energy of the products is greater than the energy of the

reactants. The opposite was true for an exothermic reaction.

products

reactants

Energy difference = 180 kJ (heat absorbed)

2 NO(g)

N2(g) + O2(g)

11. a. H C C

H H

H + H O

H

→ H C

H

H

C

H

O

H

H

b. No, it is not necessary to break all of the bonds. There are four carbon-to-hydrogen single bonds on the reactant side, and they are also in the product, ethanol. One of the oxygen-to-hydrogen bonds in water remains intact in the product.

12. a. Exothermic; a charcoal briquette releases heat as it burns. b. Endothermic; liquid water gains the necessary heat for evaporation from your skin, and your skin

feels cool. c. Endothermic; solid water gains the necessary heat from the environment to change to a liquid. d. Exothermic; wood releases heat as it undergoes combustion in your fireplace.

13. Bonds broken in the reactants 2 carbon-to-oxygen triple bonds = 2(1073 kJ) = 2146 kJ 1 oxygen-to-oxygen double bond = 1(498 kJ) = 498 kJ Total energy absorbed in breaking bonds 2644 kJ Bonds formed in the products 4 carbon-to-oxygen double bonds = 4(-803 kJ) = -3212 kJ Total energy released in forming bonds -3212 kJ Net energy change is (+2644 kJ) + (–3212 kJ) = –568 kJ Notice that the overall energy change has a negative sign, characteristic of an exothermic reaction.

CHAPTER 4: ENERGY, CHEMISTRY, AND SOCIETY

ANSWERS TO END-OF-CHAPTER QUESTIONS SECTION F PAGE 29

14.

15. a. CFCs are so stable because it takes considerable energy to break carbon-to-chlorine and

carbon-to-fluorine bonds. b. Carbon-to-chlorine bonds require 327 kJ per mole to break, and carbon-to-fluorine bonds require 485 kJ

per mole to break. This means that carbon-to-chlorine bonds are easier to break. 16. a. 2 C5H12(g) + 11 O2(g) → 10 CO(g) + 12 H2O(l) 8(356 kJ) + 24(416 kJ) + 11(498 kJ) → 10(1073 kJ) + 24(467 kJ) The net energy change is –3628 kJ and the reaction is highly exothermic. b. H2(g) + Cl2(g) → 2 HCl(g) 436 kJ + 242 kJ → 2(431 kJ) The net energy change is –184 kJ and the reaction is exothermic. c. N2(g) + 3 H2(g) → 2 NH3(g)

946 kJ + 3(436 kJ) → 6(391 kJ) The net energy change is –92 kJ and the reaction is exothermic. 17. Following the procedure in #16: a. -146 kJ; b. -498 kJ; c. -106 kJ. 18. For the U.S., the order is oil > natural gas > coal > nuclear > hydropower > other sources. This highlights

the U.S. dependence on oil for its energy needs.

19. methane (CH4): kJ 16 g kJ

x 896mol 1mol mol

56 =

propane (C2H6): kJ 44 g kJ

x 2244mol 1mol mol

51 =

hydrogen (H2): kJ 2 g kJ

x 280mol 1mol mol

140 =

ethanol (C2H6O): kJ 46 g kJ

x 1380mol 1mol mol

30 =

CHAPTER 4: ENERGY, CHEMISTRY, AND SOCIETY

SECTION F PAGE 30 ANSWERS TO END-OF-CHAPTER QUESTIONS

20. Lower limit: 1 x 106 x 9

9

50 tons Hg0.075 tons Hg

1 10 tons coal

200 tons Hg0.30 tons Hg

1 10 tons coal

=!

=!

Upper limit: 1.5 x 106 x9

200 tons Hg0.30 tons Hg

1 10 tons coal=

!

21. a. Estimating values from the graph, domestic oil production accounted for approximately 80% in

1970 (12 million barrels out of 15 million), 65% in 1980 (11 million out of 17 million), 59% in 1990 (10 out of 17 million), 48% in 2000 (9.5 out of 20 million), and is predicted to be about 36% in 2005 (8 out of 22 million).

b. Domestic oil production is falling and this means net imports are rising. c. From 1970 to 1990, there was a general rise is production from most sources other than the US and

Canada. Production from the former USSR has dropped sharply since 1987. By 2005, a more permanent decline in production is expected.

22. year 1

kcal104.2

year 1

days365

day 1

kcal000,650 8!

=!

This amount of energy can be related to each of the listed energy sources.

a. barrel

kcal107.3

barrels65

year1

year 1

kcal104.268 !

=!!

b. gallon

kcal108.8

gal 42

barrel1

barrel 1

kcal107.3 46!

=!!

c. coal ofton

kcal105.1

tons16

year1

year 1

kcal104.278 !

=!!

d.

coal of pound

kcal105.7

pounds2000

ton1

ton 1

kcal105.1 37!

=!!

23. oilpound 1

kcal101.2

oil pound 1

quarts0.56

quarts 4

gallon1

oilgallon 1

kcal108.8 44!

=!!! and

6.1kcal107.5

coal pound 1

oilpound 1

kcal101.2

3

4

=!

!!

There is 1.6 times as much energy in a pound of coal as there is in a pound of oil.

24.

No. Both of these hydrocarbons have boiling points above room temperature, so they will still be liquids at 25 °C, which is approximately room temperature.

25. a. Decane:

C C C C C C C C C

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

C

H

H

H

CHAPTER 4: ENERGY, CHEMISTRY, AND SOCIETY

ANSWERS TO END-OF-CHAPTER QUESTIONS SECTION F PAGE 31

b. The general formula for alkanes is CnH2n+2, so the formula for nonane and dodecane are C9H20 and C12H26, respectively.

c. The bond angles in all saturated hydrocarbons are 109.5 o.

26. a. H C

H

C C

H H

H

C

H

H6

C

H H

H

H

C

H

H

H

6

These bonds must break.

→H C

H

H

C C

H

H

H

H

C

H

H

C

H

H

H + H C

H

C C

H H

H

C

H

H

H

8

b. Bonds broken in the reactants 1 carbon-to-carbon single bond = 1(356 kJ) = 356 kJ 1 carbon-to-hydrogen single bond = 1(416 kJ) = 416 kJ Total energy absorbed in breaking bonds 772 kJ Bonds formed in the products 1 carbon-to-hydrogen single bond = 1(416 kJ) = 416 kJ 1 carbon-to-carbon double bond = 1(598 kJ) = 598 kJ Total energy released in forming bonds 1014 kJ Net energy change is (+772 kJ) + (–1014kJ) = –242 kJ Notice that the overall energy change has a negative sign, characteristic of an exothermic reaction.

27. There are two different isomers. H C C C C

H

H

H

H

H

H

H

H

H and H C C C

C

H

H

H H

H

H

H

H

H

28. a. Gasoline with an octane rating of 92 has the same knocking characteristics as are evident in a mixture composed of 92% isooctane and 8% heptane.

b. The octane rating does not give you any additional information about whether or not the fuel contains oxygenates. Other labels around the pump should reveal this information.

Concentrating on Concepts

29. Heat always flows from the object at higher temperature to that at lower temperature. This means that if some hot coffee is added to some cold coffee, heat will flow from the hot liquid to the cold liquid, and the final temperature of the mixture will be between the original temperatures of the two individual solutions. Heat depends on the temperature and on how much material is present. Wouldn’t you rather have a drop of hot coffee spill on you than the whole cup full at the same temperature? That is because although the drop and the cup full of coffee may initially have the same temperature, you will receive a bigger burn from the bigger volume of coffee, thanks to its larger heat content.

30. All of these refer to the idea that energy is not consumed during a chemical reaction. Energy can be transformed, but the total energy is constant during a chemical reaction. For example, when energy is transformed, it can be converted from the potential energy stored in chemical bonds to heat energy.

31. a. H2O(g) has more entropy than H2O(l) at 100 °C because the molecules can move more freely in the gas

state.

CHAPTER 4: ENERGY, CHEMISTRY, AND SOCIETY

SECTION F PAGE 32 ANSWERS TO END-OF-CHAPTER QUESTIONS

b. The iron powder has more entropy than an equal mass of solid iron because the atoms in the iron powder can move more freely than in the solid. The powder structure is more disordered, or less rigid than the solid. c. The peanut butter has more entropy than the peanuts; there are more random states possible in

peanut butter than in the whole nuts.

32. a. There is a decrease in entropy because ice is more ordered than liquid water. b. There is an increase in entropy because there are more random states for the sodium and chloride

ions dissolved in water than there are in the crystalline state. c. There is an increase in entropy because more molecules with lower mass have more possible random

states. 33. Entropy increases with increasing complexity and randomness. Diamond is a highly ordered

crystalline structure, and therefore its entropy is low. Methanol is a liquid, and the methanol molecules have greater complexity and more opportunity for random movement.

34. a. Looking only at the molar heats of combustion, octane, with more atoms and more chemical bonds,

has a greater heat of combustion than butane. However, comparisons should be based on a common base of measurement, such as the heat per gram of substance combusted. Using the molar masses of each hydrocarbon, these are the calculated heats.

188188

188

188 HC g

kJ7.47

HC g 14.21

HC mole1

HC mole1

kJ4505=! and

104104

104

104 HC g

kJ2.49

HC g 8.15

HC mole1

HC mole1

kJ2859=!

Here the trend is just the reverse. The smaller hydrocarbon gives more heat per gram than the larger hydrocarbon. Because heat comparisons should be made based on a common unit, you will have to educate your friend on this point.

b. Candle wax is composed of much larger hydrocarbons. Looking at the trends in the part a, the heat of combustion per gram is expected to be smaller and the heat of combustion per mole is expected to be larger. The lower heat per gram of wax is consistent with what your experience tells you, for a candle flame produces far less heat than burning gasoline, which contains octane.

35. a. The energy required to break a C–F bond is 485 kJ/mol, to break a C–Cl is 327 kJ/mol, and to break

a C–Br bond is 285 kJ/mol. Thus it is easiest to break a C–Br bond, so bromine free radicals rather than chlorine free radicals would be present to interact with ozone molecules.

b. This is the structure for C2F4HCl.

C C

F

F

F

F

H

Cl

The C–F bond requires 485 kJ/mol, the C–Cl bond requires 327 kJ/mol, and the C–H bond requires

416 kJ/mol, to break the bond. This means that the chlorine free radical formation requires the smallest energy input. While this seems contradictory in a replacement for halons, this compound’s lifetime in the atmosphere is significantly shorter than the atmospheric lifetimes of the halons, making it less effective in depleting ozone.

36. a. The physical property taken advantage of for separating hydrocarbons is their boiling points. b. Hydrocarbons separated at positions A and B have lower boiling points and are more volatile than

the hydrocarbons separated at position C. The hydrocarbons separated at positions A and B have fewer carbons in their structures than those separated at position C. The hydrocarbons at position D will be less volatile or not volatile at all, compared to those at position C. The hydrocarbons separated at position D have more carbon atoms than the hydrocarbons separated at C.

CHAPTER 4: ENERGY, CHEMISTRY, AND SOCIETY

ANSWERS TO END-OF-CHAPTER QUESTIONS SECTION F PAGE 33

c. The hydrocarbons separated at A will be gases, and can be used as fuels and starting materials for manufacturing. Those separated at B will be liquids, and can be used as motor fuels and as industrial solvents. Position D contains residue material that is rich in many complex compounds as well as many

carbon hydrocarbons. In addition to waxes and asphalt, these tars can be further separated into other useful compounds. The hydrocarbons separated at C are used as kerosene or diesel fuel or may be cracked.

37. a. The molecules in the liquid state should appear closer together than the molecules in the gas state. Be

sure that the molecules themselves remain intact, for no chemical bonds are broken in changing from ethene(l) to ethene(g).

b. This is a very small hydrocarbon. Figure 4.15 shows that hydrocarbons with 1-4 carbons boil at temperatures below 40 °C. The actual boiling point is –103.7 °C.

38. a. Cracking is necessary because there is more demand for the mid-range hydrocarbons that form gasoline

than can be satisfied through distillation. Heavier and lighter crude oil fractions can be manipulated to form still more gasoline through the process of cracking.

b. Cracking involves chemical processes, not just physical changes in state. Bonds are broken and bonds are formed in the process of manipulating molecules. Catalysts are used to speed the reaction.

39. a. The sketch shows that the catalyzed pathway requires less activation energy than the uncatalyzed

pathway.

Reaction

without catalyst

with catalyst

b. In Chapter 1, catalysts were discussed in connection with reducing harmful emissions from automobile

exhaust. In Chapter 2, free radical catalysts were discussed in relation to disruption of the ozone/oxygen cycle.

40. a. The text states that both octane and isooctane have essentially the same heat of combustion, so octane rating is not a measure of the energy content of a gasoline.

b. Knocking produces an objectionable metallic sound, loss of power, overheating, and possible engine damage.

c. Isooctane can be formed from octane using expensive catalysts.

41. A gasoline shortage would affect far more than just individual motorists. For example, gasoline is needed for the production and transportation of food and many other goods to consumers, and for the removal of garbage and other waste.

42. a. Each structure has the formula C8H18, so each represents octane or one of its isomers. b. Yes; structures 2 and 3 have exactly the same order of linkage. c. Each carbon-to-carbon-to-carbon bond angle is the same, the tetrahedral 109.5°. d. No, the bond angle will not change. In every isomer of octane, each carbon has four bonds and therefore

the shape around each carbon atom is tetrahedral.

CHAPTER 4: ENERGY, CHEMISTRY, AND SOCIETY

SECTION F PAGE 34 ANSWERS TO END-OF-CHAPTER QUESTIONS

e. There are several other isomers that could be sketched here. Be sure the linkage is different from the given isomers.

43. a. Eliminating the use of tetraethyl lead as an octane enhancer made finding substitute octane enhancers

necessary. b. Cities with excessive carbon monoxide emission are required by the Clean Air Act of 1990 to use

oxygenated gasoline that contains 2.7% oxygen by mass. Oxygenated gasoline is also required in the 40 U.S. cities with the highest air pollution. Students should note whether use of gasoline with added MTBE has been phased out in their area, and if so, whether the MTBE has been replaced with ethanol or another oxygen-containing compound. Alternatively, the regulation for addition of oxygenates in gasoline may have been temporarily or permanently suspended.

44. a. This depends on the basis of the comparison being made. Because oxygen atoms are already part of

the molecular structure of the added oxygenate, oxygenated fuels usually have a lower energy content than their comparative non-oxygenated fuels.

b. Oxygenated fuels often have more complexity than their non-oxygenated counterparts, leading to their having higher entropy than the non-oxygenated fuels.

45. a. Initially, the program called for gasoline to have an oxygen content of 2% by weight. VOCs had to be reduced to 15% compared to conventional gasolines. After 2000 (phase II of the program), VOC reduction had to be 25%, and NOx emissions had to be reduced by 1.5%.

b. The Year-round Reformulated Gasoline Program has been adopted by 15 areas in 10 states, accounting for 36% of the total U.S. gasoline consumption.

46. a. Vehicles designed to operate on E85 are called Flexible Fuel Vehicles (FFVs) and can function on conventional gasoline, ethanol, or a combination of the two within the same tank.

b. E85 is a blend of 85 percent ethanol and 15 percent gasoline.

c. The neighbor might be more interested in using E85 if she was from a corn producing state or from California where oxygenated fuels are in regular use.

47. a. Biodiesel fuel distributors are located primarily in the Midwest agricultural areas.

Source: http://www.biodiesel.org/buyingbiodiesel/distributors/default.shtm

b. While OK does not have many distributors, it is still fairly close to where most of the distributors are. Fla on the other hand, is a great distance from the Midwest so they might be more interested in delivery.

CHAPTER 4: ENERGY, CHEMISTRY, AND SOCIETY

ANSWERS TO END-OF-CHAPTER QUESTIONS SECTION F PAGE 35

48. a. P-Series fuel is a unique blend of natural gas liquids (pentanes plus), ethanol, and the biomass-derived co-solvent methyltetrahydrofuran (MeTHF). P-series fuels are clear, colorless, 89-93 octane, liquid blends that are formulated to be used in flexible fuel vehicles (FFV's). P-Series are designed to be used alone or freely mixed with gasoline in any proportion inside the FFV's gas tank. These fuels are not currently being produced in large quantities and are not widely used.

b. Students will have difficulty finding distributors for P-series fuels.

49. a. China's auto production had been growing by 15 per cent a year on average in the last decade. According to Beijing Traffic Administration, the number of registered motor vehicles in Beijing has doubled in a mere seven years, between 1997 and 2003.

b. Automobiles are creating pollution because of poor road infrastructure, old vehicle technology, and emission standards similar to those in the U.S. in the early 1970s. Health effects and poor crop yields are being attributed to the pollution created by this drastic increase in automobile use.

The Chinese government has already begun taken steps to try and reduce the amount of pollution by attempting to reduce emissions in the automotive population. They are doing this with aid from foreign manufactures. General Motors is aiding the Chinese government in developing proper vehicle emission standards. The government is also pursuing the electric car market with assistance from Peugeot. They are hoping to produce 5,000 electric cars per year by the beginning of the century.

Source: http://www.majbill.vt.edu/students/geog3104/group8/rtpage.html

Exploring Extensions

50. It is very hard to find any evidence for this statement on the web. There are several sites that make this assertion, but the difficulty in referencing data to support this assertion will be evident to students.

51. a. This graph shows an exothermic reaction. Note that for the reaction to proceed, energy must first be

added to the system. This is called the energy of activation. Then, as the products form, they have lower energy than the reactants from which they formed.

b. For an endothermic reaction, energy still must be added to the system to initiate the reaction. Then, the products that form have higher energies than the reactants. The diagram will look something like this.

Reaction

52. 3(N-Br kJ) + 6(467 kJ) → 3(467 kJ) + 3(234 kJ) + 3(391 kJ). The net energy change is endothermic. Solving for the energy of the nitrogen-to-bromine bond, 3(N-Br) = 555 kJ; N–Br = 185 kJ/mole

53. Hydrocarbons are separated into fractions based on their boiling points. Each of the fractions contains hydrocarbons with a range of boiling points, but they are not separated into individual hydrocarbons. Seawater contains mainly dissolved salts and water. Only two fractions could normally be separated - the water, and all the nonvolatile salts mixed together. The water can be distilled from seawater at a

CHAPTER 4: ENERGY, CHEMISTRY, AND SOCIETY

SECTION F PAGE 36 ANSWERS TO END-OF-CHAPTER QUESTIONS

temperature of 100 °C, but the salts mixed together are left behind. They are not volatile at the temperatures in a distillation column.

54. The same number and type of bonds will be broken and formed when either isomer undergoes combustion.

Therefore, there is essentially the same amount of heat released for this exothermic reaction. 55. One key is that fuel is more essential to the economic well-being of a country and its citizens than are most

other environmental issues.

56. Although coal is more abundant, oil is more convenient, has greater energy content, and is a cleaner burning fuel than coal. Coal may become the fuel of choice for the 21st century because oil supplies are lower than coal supplies. Also, technology is available to assist with the conversion of coal into oil.

57. Some of the advantages of ethanol are that it is a renewable energy source and its use does not deplete fossil fuel reserves. Some disadvantages are: widespread use of ethanol for fuel would cause diversion of land use from food supplies to fuel supplies; ethanol may be less efficient; and ethanol use may cause some engine problems. Personal positions may depend heavily on location and current price of fuel.

58. Answers will vary. Hopefully most students know the Second Law of Thermodynamics and have

read a work by Shakespeare. They may even be able to recognize that Hamlet, for example, created a world of increasing chaos and randomness that eventually led to his destruction.