<p> Chapter 4</p><p>Powering the Planet: Hydrocarbons and Fossil Fuels</p><p>Review Questions</p><p>1. Hydrocarbons are defined as compounds made up exclusively of carbon and hydrogen.</p><p>2. A carbon atom can form four bonds.</p><p>3. A hydrogen atom can form one bond.</p><p>4. Methane:</p><p>H H C H H</p><p>Ethane:</p><p>H H H C C H H H</p><p>5. Methane is a gas at room temperature because of the lack of strong attractive forces between its molecules. </p><p>6. The general molecular formula for an alkane is CmH2m+2. The general formula for an alkene is CmH2m.</p><p>7. Straight chain or unbranched carbon molecules are those in which all of the carbon atoms lie along one continuous chain. Branched hydrocarbons have carbon chains attached to the main continuous chain of carbon atoms.</p><p>8. Structural isomers are molecules with the same formula, but different structures. Butane and isobutane are examples of structural isomers.</p><p>9. There are three possible isomers.</p><p>CH2 CH2</p><p>H3C CH2 CH3</p><p>35 H3C CH3 C</p><p>H3C CH3</p><p>H3C CH2</p><p>CH CH3</p><p>H3C</p><p>10. Solvents are defined as substances, mostly in a liquid state, that dissolve many other substances. In general, polar solvents dissolve polar substances and non-polar solvents dissolve non-polar substances.</p><p>11. Cycloalkanes are alkanes in which the carbon atoms form ring structures. Cyclohexane is an example of a cycloalkane.</p><p>H H C C H H H H C C H H H H C C H H</p><p>12. a) </p><p> b) </p><p> c) </p><p>13. a) Two sources of methane gas are the decomposition of living matter in the absence of air and from termites when bacteria in their gut digests cellulose fiber.</p><p> b) Ethane is found in natural gas and oil. </p><p> c) Propane is also found in natural gas and oil.</p><p>36 d) Butane is found in natural gas and oil.</p><p>14. Four electrons are involved in a double bond, two electrons for each bond. The Lewis structure for ethane is:</p><p>H H</p><p>C C</p><p>H H </p><p>15. Alkenes are hydrocarbons containing carbon-carbon double bonds. Alkanes are hydrocarbons containing only carbon-carbon single bonds. </p><p>16. Benzene is a hydrocarbon with the molecular formula C6H6. Its has a planar structure with carbon atoms at each of the six corners of a hexagon and alternating carbon- carbon single and carbon-carbon double bonds. Benzene is called an aromatic compound because of its strong odor.</p><p>17. Currently, most of the benzene emissions come from cigarette smoke, automobile exhaust, and the evaporation of gasoline.</p><p>18. Carcinogenic substances are defined as compounds that are known to cause cancer.</p><p>19. Aromatic compounds all have ring structures with alternating carbon-carbon single and carbon-carbon double bonds.</p><p>20. Both carbon and nitrogen are non-metallic elements that form triple bonds. </p><p>21. Hydrocarbons are called fossil fuels because they burn in air to release heat and they are the residual by-products of organisms that existed hundreds of millions of years ago.</p><p>22. Proven reserves of fuel are those which are available and can definitely be exploited. </p><p>23. At the current rate of consumption of oil and natural gas, the total proven reserves represent about a 45-year supply. The reserves of coal are likely sufficient for several centuries.</p><p>24. Methane hydrates are molecules of methane held in weak combination with water.</p><p>25. Natural gas consists predominantly (60-90%) of methane gas with minor amounts of ethane, propane, n-butane, and isobutane. The exact ratio of these component gases varies depending upon the geographic origin of the deposit.</p><p>26. Methane gas is used to heat homes, fire gas stoves, and heat hot water heaters. Methane is also used for the production of commercial quantities of hydrogen gas.</p><p>37 Propane is also used for heating and cooking purposes. Because propane exists as a liquid at ambient temperatures when under pressure, propane has become popular as a fuel for motor vehicles.</p><p>27. When referring to a natural gas well, the term sour refers to those wells in which the concentration of hydrogen sulfide H2S is very high.</p><p>28. Crude oil, or petroleum, is a viscous liquid consisting of a complex mixture of alkane hydrocarbons. The exact composition varies with geographic location.</p><p>29. Crude oil is not useful as a fuel because it is a mixture of many different compounds. In order for it to be useful, it must be separated, or fractionated, into components.</p><p>30. Crude oil is separated into fractions by a process known as distillation. Using the distillation process, it is possible to separate the components of liquid mixtures into fractions by taking advantage of their different boiling points.</p><p>31. An octane number is a measure of the ability of a gasoline to generate power without engine knocking. This scale is defined at the high end by isooctane, which is assigned an arbitrary octane number of 100, and n-heptane, which is assigned an octane number of zero. The octane number of a substance is determined by matching its performance with blends of n-heptane and isooctane.</p><p>32. Lead compounds emitted from automobiles polluted the air, the vegetation, and the top level of soil in areas of high vehicle traffic, such as in cities and along interstate highways. Lead is associated with neuropsychological impairment in children, such as behavioral, intelligence, and attentiveness deficits.</p><p>33. Oil spills are a direct result of the need to transport oil long distances from its source to an area of consumption. The transportation of oil is typically done by the use of either a pipeline or an ocean tanker. Both discharge substantial amounts of oil into the environment during normal operation, and can produce significant oil spills as a result of a catastrophic failure.</p><p>34. Due to its density and composition, crude oil both floats on the surface of and is insoluble in water. The oil forms a foamy emulsion in which tiny droplets of oil become suspended in the top layer of water. Over time, the volatile components evaporate and the remaining components of the emulsion form tar balls. These tar balls persist for substantial lengths of time and either wash ashore or sink to cover shallow habitats such as coral reefs. Additionally, some of the more volatile components are absorbed by, and are toxic to, sea creatures. </p><p>35. The short-term effects of oil spills include harm to seabirds and shellfish. Long-term effects range from the destruction of mangrove trees, coral reefs, and marshes. Bottom-dwelling fish often experience disease, growth, and reproduction problems for several years following an oil spill.</p><p>38 36. Coal is composed largely of carbon and other mineral materials. It was formed from ancient plant matter, called peat, that was partially decomposed before it was covered by either mud or water and could not be oxidized to CO2. Over several million years, the peat was geochemically changed into coal.</p><p>37. Peat is the partially decomposed remains of land-based woody plants produced from the action of microorganisms. Peat, when covered by water and minerals, cannot undergo further oxidation and is geochemically changed to coal. </p><p>38. Strip mining is a form of mining in which a large area of the surface soil, rock and vegetation are removed to expose the coal. In addition to being unsightly, the exposed soil is readily washed away by rain producing further environmental destruction.</p><p>39. Coal is called a “dirty fuel” because in addition to carbon, coal contains measurable quantities of most of the naturally occurring elements. As a result, the burning of coal produces or liberates substantial amounts of air pollutants, such as sulfur dioxide, nitric oxide, fluoride compounds, heavy metals, and even radioactive metals like uranium.</p><p>Understanding Concepts</p><p>40. Methane, ethane, propane, and butane are all small non-polar hydrocarbons molecules with very weak attractive forces between their molecules. As a result, they have very low boiling points and exist as gases at ambient temperatures.</p><p>41. a) CH3CH2CH2CH2CH2CH2CH2CH3</p><p> b) CH3CH2CH2CH2CH2CH2CH3 c) C5H10 or</p><p>CH2</p><p>H2C CH2</p><p>CH2 CH2</p><p> d) CH2CHCHCHCH2 or CH2=CH-CH=CH-CH2</p><p>42. The general formula for an alkane is CmH2m+2 and for an alkene is CmH2m.</p><p> a) alkane: C4H10; alkene: C4H8</p><p>39 b) alkane: C6H14; alkene: C6H12</p><p> c) alkane: C8H18; alkene: C8H16</p><p>43. a)</p><p> b) 0</p><p>44. C7H16</p><p> a) CH2 CH2 CH2 H3C CH2 CH2 CH3</p><p> b) CH3</p><p>HC CH2 CH3 H3C CH2 CH2 c)</p><p>CH3</p><p>CH CH2 H2C CH2 CH3</p><p>CH3 d) H3C CH2</p><p>CH CH3 H2C CH2</p><p>CH3</p><p> e)</p><p>40 CH H3C 3 HC</p><p>CH CH CH2 3</p><p>H3C f) CH3 H3C CH</p><p>CH2</p><p>HC CH3 H3C g)</p><p>H3C CH3 CH</p><p>H3C C CH3</p><p>CH3 h) CH3</p><p>CH2 CH2 H3C C</p><p>CH3 H3C i) </p><p>H3C CH2 C CH3 H2C CH3 CH3</p><p>C6H14</p><p>41 a) </p><p>CH2 CH2 CH3 H3C CH2 CH2</p><p> b) CH3</p><p>CH CH2 H3C CH2 CH3</p><p> c) </p><p>CH3</p><p>CH CH3</p><p>H3C CH</p><p>CH3</p><p> d)</p><p>CH3</p><p>H3C C CH2</p><p>CH3 CH3</p><p> e) CH2 CH2</p><p>H3C CH CH3</p><p>CH3</p><p>45. a) unique isomers (2-methylpentane and n-hexane)</p><p>42 b) duplicates (both are n-hexane)</p><p> c) duplicates (both are 2,3-dimethylpentane)</p><p>46. Ethane and ethene are both hydrocarbons with two carbon atoms and both exist as gases at ambient temperatures and pressures. Ethane has six hydrogen atoms while ethene has four hydrogen atoms. Further, ethene has a double bond between the carbon atoms resulting in a trigonal planar geometry for each carbon atom while ethane has a single bond between the carbon atoms resulting in a tetrahedral configuration around each of its carbon atoms. The C=C bond of ethane does not undergo free rotation while the C-C bond of ethane does.</p><p>47. Hydrocarbons make good solvents because they are non-polar in character. As a result, they are able to readily dissolve non-polar materials such as dirt and oils.</p><p>48. Hydrocarbons with more than six carbon atoms are liquids or solids at room temperature because they have stronger attractive forces between their molecules than those hydrocarbons with less than six carbon atoms.</p><p>49. As a result of the vast quantities of natural gas that exist as methane hydrates and/or buried in poorly accessible locations, oil is more easily extracted from the earth than natural gas.</p><p>50. Hydrocarbons are useful as fuels because they burn readily in oxygen to produce substantial amounts of heat. Because of the lack of oxygen in the parent hydrocarbon molecules, these materials generate more heat per gram than compounds of similar molecular weight and composition that contain oxygen. In addition, many hydrocarbons are easily transported and stored.</p><p>51. Alkanes of more than 12 carbons cannot be used in gasoline because they do not sufficiently evaporate in the engine to properly burn.</p><p>52. The octane number for gasoline is a measurement of the ability of a gasoline to generate power without knocking. Because highly branched alkanes are less likely to exhibit premature ignition, these materials have excellent burning characteristics for internal combustion engines. Thus, on the octane scale, isooctane is assigned an octane number of 100, and n-heptane, a straight chain alkane with seven carbon atoms, is assigned an octane number of 0. Intermediate blends containing various concentrations of branched and unbranched alkanes have intermediate octane numbers. Therefore, a gasoline with an octane number of 100 is equivalent to isooctane, while that with an octane number of 55 has a higher concentration of unbranched alkanes and a lower concentration of branched alkanes.</p><p>53. In a closed container containing hydrocarbons of fewer and more than five carbon atoms, the hydrocarbons with fewer than five carbon atoms will occupy the greatest percentage of space above the liquid. This results from the fact that hydrocarbons</p><p>43 with fewer than five carbon atoms will vaporize to the greatest extent, while those with five or more carbons will vaporize to a relatively lesser extent.</p><p>Synthesizing Ideas</p><p>54. H</p><p>H Si H</p><p>H</p><p>55. </p><p>H N H</p><p>H</p><p>56. H</p><p>H C H</p><p>H</p><p>H</p><p>H C H</p><p>H</p><p>The angles between the bonds in a tetrahedron are 109.5o, while those in the square planar arrangement are 90o. Since electrons are negatively charged and repel each other, the tetrahedral arrangement provides a greater distance between the electron pairs and is, therefore, the more stable structure.</p><p>57. No, such a molecule cannot exist. Carbon can only form four bonds. In the molecule proposed, one carbon would have five bonds (four to hydrogen and one to carbon) and the other carbon would have three bonds (two to hydrogen and one to carbon).</p><p>58. a) In this structure, there are two O-H bonds and one O-O bond. Both oxygen atoms and one hydrogen atom are in the plane of the paper, while one hydrogen atom extends out from the paper. </p><p> b) In this representation, there are two O-H bonds and one O-O bond. The three- dimensional orientation of the atoms is not indicated in this structure.</p><p>44 59. The general formula for alkanes is CmH2m+2. Therefore, 202 hydrogen atoms would be required in an n-alkane with 100 carbon atoms.</p><p>60. Simple cycloalkane molecules have equal numbers of carbon atoms, but two fewer hydrogen atoms than the corresponding non-cyclic alkane. Therefore, the general formula for cycloalkanes that have all of their “m” carbon atoms in a continuous ring is CmH2m.</p><p>61. Two possible conformations for butadiene are given below:</p><p>CH CH2</p><p>H2C CH</p><p>CH2 HC</p><p>HC</p><p>CH2</p><p>Due to free rotation around the C-C single bond, these two conformations cannot be isolated.</p><p>62. Step 1: Calculate the number of molecules of C30H62 in 0.775 grams of C30H62.</p><p>1.1 x 10 21 molecules = x molecules 1 gram 0.775 g</p><p> x = 8.5 x 1020 molecules </p><p>Since there are 8.5 x 1020 molecules in 0.775 grams and 0.775 grams occupies 1 cm3, then there must be 8.5 x 1020 molecules in 1cm3.</p><p>Step 2: Since cm3 is a volume unit, calculate the volume of one molecule.</p><p>8.5 x 10 20 molecules = 1 molecule 1 cm3 x cm3</p><p> x = 1.17 x 10-21 cm3</p><p>-21 3 Therefore, the volume of one molecule of C30H62 is 1.17 x 10 cm .</p><p>The dimension of the cube is 1.05 x 10-7 cm by 1.05 x 10-7 cm by 1.05 x 10-7 cm.</p><p>63. a) H2S + O2  SO2 + H2O</p><p>45 i) 2 H2S + 3 O2  2 SO2 + 2 H2O</p><p> b) H2S + SO2  S + H2O</p><p> i) 8 H2S + 4 SO2  12 S + 8 H2O which reduces to:</p><p>2 H2S + SO2  3 S + 2 H2O</p><p> ii) In order to consume all of the SO2 produced in a) you need to multiply the balanced reaction b) by 2. Thus,</p><p>4 H2S + 2 SO2  6 S + 4 H2O</p><p> iii) Adding both the reactions yields the following net equation:</p><p>2 H2S + 3 O2  2 SO2 + 2 H2O</p><p>+ 4 H2S + 2 SO2  6 S + 4 H2O</p><p>6 H2S + 3 O2  6 S + 6 H2O which reduces to:</p><p>2 H2S + O2  2 S + 2 H2O</p><p>64. Gasoline is volatile and is readily converted into the vapor state. This vapor can travel to a flame source distant from the liquid and ignite.</p><p>65. The four types of coal are young coal or peat with about 60% carbon, brown coal or lignite with about 70% carbon, soft coal or bituminous with about 85-90% carbon, and hard coal or anthracite with about 95% carbon. The type of coal with the highest oxygen content has the lowest carbon content. Thus, young coal or peat has the highest oxygen content. Materials with the lowest oxygen content have the highest fuel value. Hard coal or anthracite has the highest fuel value.</p><p>46</p>