MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.

Transcription

1 MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) Models of planet formation suggest that Earth was molten during the early stages of its formation. Why? A) The entire Solar System was extremely hot at the time. B) The heat generated by large impacts from extraterrestrial sources would melt any solid rocks. C) It was closer to the Sun at that time. D) Many volcanoes were active. 1) 2) Which of the following is not needed to calculate the age of a rock using radiometric dating? 2) A) the ratio of parent to daughter isotope when the rock formed B) the half-life of the parent isotope C) the current ratio of parent to daughter isotope D) the types of fossils found near the rock in question 3) If the Earth was molten at the time that it formed, no solid rocks date from that period. How do scientists determine when Earth formed? A) They assume meteorites and other space rocks formed at the same time, and they date those. B) They estimate how long it would have taken for particles from the Big Bang to reach this part of the solar system. C) Radiometric dating is most easily performed on molten rocks. D) They can estimate how long the molten Earth took to cool and form the thickness of crust observed today, with the center remaining molten. 4) Potassium-40 decays to argon-40 with a half-life of 1.3 billion years. When a volcano erupts and the molten rock cools, it contains 100% 40K and 0% 40Ar (because argon is a gas). A researcher found a fossil in volcanic rocks that contains 25% 40K and 75% 40Ar. How long ago did the fossilized organism live? A) 5.2 billion years ago B) 1.3 billion years ago C) 3.9 billion years ago D) 2.6 billion years ago 5) Carbon-14 decays to nitrogen-14 with a half-life of 5730 years. When wood burns, the charcoal that remains contains 100% 14C and 0% 14N. A researcher found some stone tools next to charcoal containing 12.5% 14C and 87.5% 14N. How long ago did the presumed campfire take place? A) 17,190 years ago B) 11,460 years ago C) 5730 years ago D) 22,290 years ago 3) 4) 5) 6) Which of the following is an important assumption used in radiometric dating? 6) A) The rate of radioactive decay is a function of the amount of parent isotope. B) The rate of radioactive decay is a function of the age of the rock. C) The rate of radioactive decay has been constant through time. D) The rate of radioactive decay is a function of the amount of daughter isotope. 1

2 7) Suppose a researcher announced the discovery of a fossil that is 4.5 billion years old. Why would you be skeptical of this claim? A) Chemical evolution was completed by that time. B) The fossil record is incomplete. C) Radiometric dating methods are not reliable for rocks that ancient. D) According to current models and data, the planet was probably molten at the time. 7) The following paragraph relates to the questions below: According to Laura F. Robinson, scientists can learn about past weather conditions by studying the ratio of two isotopes of the element uranium found in rivers and seas. In this study, Robinson suggests that movement of New Zealand glaciers during the most recent ice age was affected more by increased rainfall rather than, as an earlier report suggested, that glacier movement was due primarily to a cooling effect. The amounts of the two uranium isotopes are related because the higher-mass isotope (with a mass number of 238) undergoes three nuclear reactions (radioactive decay) and turns into the lower-mass isotope. Thus, as the amount of the heavier isotope in rivers drops, the amount of the lighter isotope rises. The heavier isotope undergoes three nuclear reactions, resulting in a total loss of four neutrons. [Source: L. F. Robinson et al., Science 305 (851): 2004.] 8) What is the mass number of the lighter isotope of uranium used by Robinson in this study? 8) A) 238 B) 234 C) 235 D) 242 9) The U-238 isotope has 92 protons. After it undergoes its three nuclear reactions and turns into the lighter uranium isotope, how many protons are left? A) 92 B) 90 C) 88 D) 89 9) 10) How many neutrons are in the lighter isotope? 10) A) 88 B) 92 C) 234 D) ) How many electrons are involved in a single covalent bond? 11) A) one B) two C) four D) three 12) How many electrons are involved in a double covalent bond? 12) A) four B) three C) two D) one 13) How many electrons are involved in a triple covalent bond? 13) A) two B) three C) nine D) six 14) If an atom has a charge of +1, which of the following is true? 14) A) It has the same number of protons as neutrons. B) It has one more electron than it does protons. C) It has the same number of protons as electrons. D) It has one more proton than it does electrons. 2

3 15) If an atom has a charge of -2, which of the following is true? 15) A) It has two more neutrons than electrons. B) It has two more electrons than protons. C) It has two more protons than electrons. D) It has two more protons than neutrons. 16) If an atom is electrically neutral, which of the following is true? 16) A) It has at least one more electron than it does protons. B) It has the same number of protons as electrons. C) It has the same number of protons as neutrons. D) It has the same number of neutrons as electrons. 17) An atom has six electrons in its valence shell. How many bonds would you expect it to form in most circumstances? A) three B) two C) six D) one 18) An atom has four electrons in its valence shell. What types of covalent bonds is it capable of forming? A) four single bonds only B) two double bonds only C) single and double only D) single, double, or triple 17) 18) 19) When are atoms most stable? 19) A) when they have the fewest possible valence electrons B) when all electrons are paired C) when all of the electron orbitals in the valence shell are filled D) when they have the maximum number of unpaired electrons 20) What holds electrons in a covalent bond? 20) A) An increase in potential energy, caused by electrical repulsion of the electrons in the bond, holds the electrons. B) It is the fact that two electrons are paired in the same orbital. C) The electron sharing that occurs makes the atoms involved smaller and more compact. D) The negative charges on the electrons are attracted by the positive charges on both nuclei. 21) How can you determine the approximate mass of an atom, in atomic mass units? 21) A) Add up the number of protons and neutrons. B) Add up the number of protons and electrons. C) Add up the number of protons, electrons, and neutrons. D) Take the number of protons minus the number of electrons. 22) When one of the atoms involved in a covalent bond has a much higher electronegativity than the other atom, what type of bond results? A) a double bond B) a polar covalent bond C) a nonpolar covalent bond D) a hydrogen bond 22) 3

4 23) When the atoms involved in a covalent bond have the same electronegativity, what type of bond results? A) a polar covalent bond B) a nonpolar covalent bond C) a double bond D) a hydrogen bond 24) The difference between a polar covalent bond and an ionic bond is that electrons are shared unequally in a polar covalent bond but completely transferred (i.e., not shared) in an ionic bond. A) True B) False 25) Nitrogen normally forms only three bonds because it has a valence of 5. However, in a certain nitrogen molecule, it has four bonds to four hydrogens (hydrogen has a valence of 1). Make a sketch of this molecule. Count the number of electrons in your sketch. Compare this number to the number of valence electrons in 1 N and 4 H's. What do you predict to be the charge on this molecule? A) +1 B) -2 C) -1 D) +2 26) The structural formula for a certain molecule includes a group symbolized -O. The dash next to the oxygen atom means that a single bond exists to another atom, such as a carbon. Based on the valence of oxygen and the number of bonds it normally forms, what is the charge on the oxygen atom in this case? A) -2 B) -1 C) +2 D) +1 27) You need to write down information about a molecule, but need to indicate only which atoms it contains and how many of each. Which representation would work best? A) structural formula B) space-filling model C) ball-and-stick model D) molecular formula 28) You need to write down information about a molecule that gives the most accurate picture of the relative sizes of the atoms involved and their relationship in space. Which representation would work best? A) molecular formula B) ball-and-stick model C) space-filling model D) structural formula 29) Consider the following reaction at equilibrium: CO2 + H2O? H2CO3. What would be the effect of adding additional H2CO3? A) The amounts of CO2 and H2O would decrease. B) It would drive the equilibrium dynamics to the left. C) Nothing would happen, because the reactants and products are in equilibrium. D) It would drive the equilibrium dynamics to the right. 23) 24) 25) 26) 27) 28) 29) 4

5 30) Which of the following is a violation of the first law of thermodynamics? 30) A) All of the energy in the universe today was present when the Big Bang occurred. B) The universe will eventually die, and will have no energy left in it. C) The amount of energy stored in a plant's cell as sugars after undergoing photosynthesis is less than the amount of sunlight it absorbed. D) A hydrogen bomb can destroy a large city with only a few pounds of explosive material. 31) Which reaction is most spontaneous? 31) A) a reaction that is slightly endothermic and leads to a huge decrease in entropy B) a reaction that is slightly exothermic and leads to a huge increase in entropy C) a reaction that is slightly exothermic and leads to a slight increase in entropy D) a reaction that is highly exothermic and leads to a huge decrease in entropy 32) Why are some reactions exothermic? 32) A) The products have lower potential energy than the reactants. B) They are spontaneous. C) The products have higher entropy (are more disordered) than the reactants. D) They are non-spontaneous. 33) Ice melts spontaneously at room temperature, even though the process is endothermic. How is this possible? A) H is small, so melting still obeys the second law of thermodynamics. B) The Gibbs free-energy relationship does not apply to phase changes such as melting. C) There is a large increase in entropy. D) Water has a very high specific heat. 33) 34) What does it mean to say a system has a G equal to zero? 34) A) The system does not release or absorb heat. B) The total amount of potential energy in the system is zero. C) The system is at equilibrium. D) The system is perfectly ordered (no entropy). 35) In the Gibbs free-energy relationship, why is the T term necessary? 35) A) The change in potential energy is a function of temperature. B) The change in entropy is a function of temperature. C) The change in kinetic energy is a function of temperature. 36) Which statement best summarizes the essence of chemical evolution? 36) A) Entropy increased. B) Instead of being radiated back to space, energy in the form of sunlight or heat was retained in the oceans and atmosphere because of water's high specific heat. C) Energy in the form of sunlight or heat was transformed into chemical energy. D) An increasing number of exothermic reactions occurred. 5

6 37) Why do chemical reactions tend to speed up when the reactants are heated? 37) A) The reactants collide more often. B) The reactants move faster. C) The reactants have greater energy. D) All of the above apply. 38) Why do chemical reactions tend to speed up when the concentration of the reactants is increased? 38) A) The reactants move faster. B) The reactants have greater energy. C) The reactants collide more often. D) All of the above apply. 39) During chemical evolution, which of the following occurred in the molecules involved? 39) A) Entropy stayed constant while potential energy increased. B) Entropy increased while potential energy increased. C) Entropy decreased while potential energy increased. 40) Chemical evolution refers to which of the following? 40) A) Water condensed to form the first oceans. B) Large molecules tended to break apart because of the intense sunlight and heat from volcanoes. C) Earth's crust solidified, even as massive bombardment from outer space continued. D) Small molecules reacted to form larger, more complex molecules. 41) You've been asked to analyze a reaction that took place at 300 K. H was -150 and S was Is the reaction endothermic or exothermic? A) You cannot tell unless you know the amount of disorder in the reactants and products. B) exothermic C) endothermic D) You cannot tell unless you know the potential energy of the reactants and products. 41) 42) What does it mean to say that a molecule such as H2 or CH4 is reduced? 42) A) It is likely to act as an electron acceptor in redox reactions. B) It is small in size. C) It has relatively high potential energy. D) It is likely to form free radicals when struck by sunlight. 43) Reduction refers to which of the following? 43) A) electrons moving away from an atom's nucleus B) electrons being transferred to another atom C) electrons moving closer to an atom's nucleus D) all of the above 6

7 44) Oxidation refers to which of the following? 44) A) electrons moving away from an atom's nucleus B) electrons being gained from another atom C) electrons moving closer to an atom's nucleus D) all of the above 45) Which of the following is true of redox reactions? 45) A) Oxidation can occur alone in some cases. B) Oxidation and reduction must always occur together. C) Reduction can occur alone in some cases. 46) Which of the following tends to make chemical reactions spontaneous? 46) A) The reactants have lower potential energy than the products. B) The reactants are more ordered than the products. C) The pressure is low. D) The temperature is low. 47) Why were reduced compounds such as H2, CH4, and NH3 required for chemical evolution to get started? A) They could act as electron acceptors in redox reactions. B) They could act as electron donors in redox reactions. C) They contain the atoms most likely to be found in living organisms. D) They all have polar covalent bonds. 47) The following paragraph relates to the questions below: Eric A. Davidson et al. have reported on a model that helps atmospheric scientists relate chemical and biological activity within soils to the release of nitrogen oxides into the atmosphere. A significant attempt of this model is to understand the forces that give rise to atmospheric nitrous oxide (N 2 O) and nitric oxide (NO). The first compound is important because it is known to destroy ozone in the stratosphere; the second one is important because it produces ozone in the troposphere. The significance of ozone in the troposphere includes the fact that it acts as a respiratory irritant to humans and, according to Davidson, reduces crop yields. Both of these compounds, along with atmospheric nitrogen (N2), are tied together in a series of biological and chemical processes occurring within soil and the atmosphere. Furthermore, the fact that nitrogen has a lower electronegativity than oxygen suggests many interesting things about its chemistry. [Source: E. A. Davidson et al., BioScience 50 (667): 2000.] 48) Based on what you know about oxidation-reduction processes in carbon compounds, which of the three compounds discussed here (N2, N2O, and NO) has the most reduced nitrogens? A) N2O B) N2 C) NO 48) 7

8 49) Davidson states that NO is the most oxidized of the three nitrogen gases discussed. What does this tell us about the relationship between N2O and NO? A) NO has more energy stored in its electrons than N2O. B) The potential energy of electrons in NO is lower than in N2O. C) Based on energetics alone, NO can be converted into N2 more easily than N2O can be converted into N2. D) The electrons in NO are located closer to the nitrogen than are those in N2O. 49) 50) Why is water capable of forming hydrogen bonds? 50) A) It is highly polar. B) The hydrogen atoms carry partial positive charges. C) The oxygen atom carries a partial negative charge. D) All of the above apply. 51) Why is water such a good solvent? 51) A) It can participate in hydrogen bonds. B) It is highly polar. C) Most polar and charged substances dissolve in it. D) All of the above apply. 52) Which of the following is not a property of liquid water? 52) A) Its density is greater than ice. B) Its heat of vaporization is lower than that for most other substances. C) Its specific heat is higher than that for most other substances. D) It is polar. 53) Which of the following true statements can be attributed to water's high specific heat? 53) A) Our bodies feel cooler when the sweat on our skin evaporates. B) Ice floats on water. C) Our body temperature takes a long time to change because it is composed mostly of water. D) Sugar dissolves in hot tea faster than in iced tea. 54) The ability to sweat or pant is considered an adaptation. Why? 54) A) It allows a body to release excess water. B) It cools a body off, due to water's high heat of vaporization. C) It is an important signal to others that an individual is too hot. D) It allows a body to absorb heat, due to water's high specific heat. 8

9 55) The cities of Portland, Oregon, and Minneapolis, Minnesota, are at about the same latitude, but Minneapolis has much hotter summers and much colder winters than Portland does. Why? (Portland is near the Pacific Ocean; Minneapolis is near a number of large lakes.) A) The ocean is so large that it has a highly moderating influence on temperature. B) Freshwater is more likely to freeze than saltwater. C) They are not at exactly the same latitude. D) Minneapolis is much windier, due to its location in the middle of a continent. 56) To act as an effective coolant in a car's radiator, a substance has to be a liquid at the temperatures found in your car's engine and have the capacity to absorb a great deal of heat. You have a reference book with tables listing the physical properties of many liquids. In choosing a coolant for your car, which table would you check first? A) density at room temperature B) heat of vaporization C) specific heat D) ph 57) Doctors used to recommend that parents sponge feverish children with rubbing alcohol to lower their body temperature. Rubbing alcohol has a lower heat of vaporization than water does. Which of the following is true? A) Rubbing alcohol will evaporate more slowly than water. B) Rubbing alcohol will evaporate at the same rate as water. C) Rubbing alcohol will evaporate faster than water. 55) 56) 57) 58) Which of the following has the most potential energy? (Choose all that apply.) 58) A) an electron that is part of a nonpolar covalent bond B) an electron that is part of a polar covalent bond C) an electron in the first shell D) an electron in the fourth shell, D 59) Which of the following occurs when a covalent bond forms? 59) A) Electrons in valence shells are shared between nuclei. B) Ions of opposite charge interact. C) Polar molecules interact. D) The potential energy of electrons drops. 60) If a reaction is exothermic, then which of the following statements is true? 60) A) Energy must be added for the reaction to proceed. B) The products have higher entropy (are more disordered) than the reactants. C) It occurs extremely quickly. D) The products have lower potential energy than the reactants. 9

10 61) What is thermal energy? 61) A) the temperature increase that occurs when any form of energy is added to a system B) a form of potential energy C) mechanical energy D) the kinetic energy of molecular motion, measured as heat 62) What determines whether a chemical reaction is spontaneous? 62) A) if it increases the disorder, or entropy, of the substances involved B) the temperature only; reactions are spontaneous at high temperatures and nonspontaneous at low temperatures C) the combined effect of changes in potential energy and entropy D) if it decreases the potential energy of the substances involved 63) Which of the following is not an example of an energy transformation? 63) A) The electrical energy flowing through a light bulb's filament is converted into light and heat. B) A chemical reaction converts the energy in sunlight into the chemical energy in formaldehyde. C) Sunlight strikes a prism and separates into many distinct wavelengths. D) A shoe drops, converting potential energy to kinetic energy. 64) When an atom is reduced, it 64) A) gains an electron B) loses entropy C) loses an electron D) gains entropy 10

11 SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 65) Section 2.2 describes the reaction between carbon dioxide and water, which forms carbonic acid: 65) CO 2 (g) + H 2 O (l) H 2 CO (aq) In aqueous solution, carbonic acid immediately dissociates to form a proton and the bicarbonate ion, as follows: H2 CO3 (aq) H+ (aq) + HCO3 - (aq) Does this reaction raise or lower the ph of the solution? Does the bicarbonate ion act as an acid or a base? If an underwater volcano bubbled additional CO2 into the ocean, would this sequence of reactions be driven to the left or the right? How would this affect the ph of the ocean? Answer: The reaction between carbon dioxide and water lowers the ph of the solution, as long as CO2 is readily available and the reaction continues in the forward direction. The bicarbonate ion acts as a base. If additional CO2 is added, the sequence of reactions would be driven to the right, which would make the ocean more acidic. (This same reaction occurs in the bloodstream, when CO2 enters the blood from active muscles. The H + that is generated inside red blood cells acidifies the cell, which causes hemoglobin to change shape slightly and release more oxygen. The bicarbonate ion diffuses into the blood plasma and is a major buffer component in the blood). 66) When chemistry texts introduce the concept of electron shells, they emphasize that shells represent distinct potential energy levels. In introducing electron shells, this chapter also emphasized that they represent distinct distances from the positive charges in the nucleus. Are these two points of view in conflict? Why or why not? Answer: The view that electron shells represent distinct potential energy levels is not in conflict with the view that electron shells represent distinct distances from the positive charges in the nucleus. The reasoning is that shells that are farther from the protons in the nucleus will house electrons that have greater potential energy than shells closer to the nucleus, because electrons in outer shells will fall into inner shells if an opportunity arises. 66) 11

12 67) In using radiometric dating to estimate when a rock formed, geologists must know three quantities. What are they? How are they used to estimate the age of a rock sample? What sources of uncertainty are involved in measuring these three quantities? Answer: The three quantities that geologists must know to estimate the age of a rock are a. ratio of parent isotope to daughter isotope in the rock b. an assumption or estimate of the ratio of parent isotope to daughter isotope under the conditions that prevailed at the time the rock formed c. the half-life of the parent isotope 67) By knowing these three quantities, geologists can determine the number of elapsed half-lives that have taken place to give the current ratio of parent-to-daughter isotope. From that number, they can calculate the number of years since the rock formed. There is uncertainty in determining what the original ratio of parent-to-daughter isotope was at the time the rock formed. Geologists must guess at or estimate this ratio from any data available regarding the abundance of the parent and daughter isotopes at that time. Also, if the daughter isotope is itself unstable, then the half-life of its decay must also be taken into account. Ratios of parent isotope to daughter isotope, as well as half-life values, can be measured accurately with a great deal of certainty. 68) Why does ice float? 68) Answer: Ice floats because, as it freezes, the more disorganized and densely packed H2O molecules form a highly regular and less dense crystal structure with fewer H2O molecules per volume than are found in liquid water. 69) Hydrogen bonds form because the opposite, partial electric charges on polar molecules attract. Covalent bonds form as a result of the electrical attraction between electrons and protons. Covalent bonds are much stronger than hydrogen bonds. Explain why, in terms of the electrical attractions involved. covalent bond is a much stronger bond than a hydrogen bond because, in a covalent bond, the electrical attractions between (+) and (-) are shared over both atoms participating in the covalent bond. This is because each electron participating in the covalent bond is attracted to both nuclei of the atoms linked by the bond. In a hydrogen bond, the (+) and (-) charges are only partial, and the attraction between them does not involve sharing of electrons. Instead, the bond is simply the result of attraction between opposite charges. Hydrogen bonds between any two polar molecules can, therefore, be easily broken by the presence of another polar molecule. 69) 12

13 70) Draw a ball-and-stick model of the water molecule, and explain why this molecule is bent. Indicate the location of the partial electric charges on it. Why do these partial charges exist? Answer: Water molecules are bent due to the geometry of the covalent bonds that join the hydrogen atoms to the oxygen atom. The electron orbitals surrounding oxygen are in a tetrahedron conformation. Two of these orbitals are shared with hydrogen atoms, so the resulting water molecule has a bent shape. The partial charges exist on these molecules because the electrons are not shared equally between oxygen and hydrogen. Since oxygen's nucleus has more protons than hydrogen has, the shared electrons in the covalent bond are pulled closer to oxygen. For this reason, oxygen has a small negative charge and the hydrogen atoms have a small positive charge. 70) 71) Suppose you wanted to use radiometric dating to estimate the age of an archaeological site that was thought to be about 1500 years old. Would you use the uranium-lead system described in Section 2.1, or would you evaluate a radioisotope that had a shorter half-life? Explain your answer. Answer: The uranium-lead isotope system would not be useful in estimating an archaeological site using radiometric dating, because its half-life of 713 million years is vastly greater than the age of archaeological sites. An isotope that has a much shorter half-life would be needed to be able to see the "ticking clock." 71) Figure ) Oxygen is extremely electronegative, meaning that its nucleus pulls in electrons shared in covalent bonds. Because these electrons are close to the oxygen nucleus, they have lower potential energy. Explain the changes in electron position that are illustrated in Figure 2.20 in terms of oxygen's electronegativity. Answer: The changes in electron position (orange dots) that are illustrated in Figure 2.20 can be explained by oxygen's electronegativity oxygen is much more electronegative than either carbon or hydrogen. When oxygen is present in a molecule, the electrons of a covalent bond will spend more time near the oxygen atom. Carbon and hydrogen have roughly similar electronegativities, and they tend to share the electrons of a covalent bond more equally. 72) 13

14 73) When nuclear reactions take place, some of the mass in the atoms involved is converted to energy. The energy in sunlight is created during nuclear fusion reactions on the Sun. Explain what astronomers mean when they say that the Sun is burning down and that it will eventually burn out. Answer: The mass of the atoms in the Sun is converted to radiant energy during nuclear fusion reactions, and this energy is released in the form of sunlight, so the Sun will burn out when the mass of its component atoms is finally depleted. 74) Why do coastal regions tend to have climates with moderate temperatures and lower annual variation in temperature than do inland areas at the same latitude? oastal regions tend to have climates with moderate temperatures because they are close to large bodies of water. Since water has a high heat of vaporization, it tends to absorb heat, thus moderating temperature. The hydrogen bonds between water molecules give water a moderating influence on temperature. 73) 74) MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 75) Two isotopes of an element vary in the number of. 75) A) protons B) electrons C) neutrons 76) The number of within an atom never varies among atoms of a specific element. 76) A) electrons B) protons C) neutrons 77) The most ancient fossils are in rocks that formed. 77) A) 3.8 Ga B) 4.4 Ga C) 4.4 billion years ago D) 65 million years ago 78) 3.5 Ga is about five times the half-life for uranium's decay to lead. What ratio of uranium to lead would researchers find in a fossil from 3.5 Ga? A) 1 part uranium to 32 parts lead B) 1 part uranium to 25 parts lead C) 1 part uranium to 1 part lead D) 1 part uranium to 5 parts lead 78) 79) An organic molecule always contains one or more atoms of: 79) A) carbon B) oxygen C) sulfur D) nitrogen 80) 96% of matter found in living organisms is composed of these four elements: 80) A) sulfur, hydrogen, oxygen, nitrogen B) hydrogen, carbon, oxygen, sulfur C) carbon, sulfur, nitrogen, iron D) hydrogen, carbon, oxygen, nitrogen 81) A large boulder is balanced on top of a hill. You give the boulder a push, and it rolls down the hill. This is an example of transferring energy into energy. A) kinetic; thermal B) kinetic; potential C) potential; kinetic 81) 14

15 82) Which phase of matter has the highest entropy? 82) A) gas B) liquid C) solid 83) Substances that give up protons H+ during acid-base reactions are: 83) A) ions B) acids C) bases D) isotopes 84) How many protons are present in 1 liter of pure water? (Hint: See definition of molarity). 84) A) B) C) D) No protons are present. 85) A cation has a charge. 85) A) neutral B) negative C) positive 86) Which of the following were necessary to produce formaldehyde and cyanide, the first reduced-carbon products, on ancient Earth? A) atmospheric molecules: NH3, CO2, CO, N2, H2O B) energy from sunlight C) energy from heat D) Answers A and B are correct. E) Answers A and C are correct. 87) Following formation of reduced-carbon compounds, the addition of heat allowed bonds to form. A) carbon to carbon B) carbon to hydrogen C) carbon to oxygen D) hydrogen to oxygen 86) 87) SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 88) Computer models of chemical reactions in ancient Earth's atmosphere are discussed in this chapter. What assumptions about the environment on ancient Earth were made by the programmers? Did the results of the computer simulations support or reject the chemical evolution hypothesis? Answer: They assumed that Earth's early atmosphere contained CH4, NH3, H2O, CO2, H2, and N2 exposed to sunlight (this assumption is supported by the best current data about ancient Earth's environment). Their models supported the chemical evolution hypothesis because reduced carbon compounds were made that can combine to form organic molecules when heat is present. 89) H, C, N and O are the most prevalent atoms in organic compounds. Why do these atoms combine to form molecules like H2O, CO2, H2 and N2? Answer: These atoms combine to form these molecules because they have unpaired electrons in their outer orbitals and are not stable as lone atoms, but are stable when they fill their outer orbitals by sharing electrons in covalent bonds. 88) 89) 15

16 90) Look at the reaction: CO2(g) + 2 H2O(g) H2CO(g) + H2O(g). Is H positive or negative? Is S positive or negative? How about G? Will this reaction proceed spontaneously? Answer: H is positive because more bonds are created than broken; the products have more potential energy. S is negative because there are fewer molecules and therefore less entropy in the products than in the reactants. G must be positive, and this reaction will not proceed spontaneously an energy source (e.g., sunlight) must be present in order for it to occur. 90) 91) A nitrogen atom has 7 protons and 7 neutrons. What is its atomic number? What is its mass number? What is the molecular weight of molecular nitrogen (nitrogen gas, N 2 )? What type of bond holds N2 together (be specific)? How much would a mole of N2 weigh? Is the bond that holds N 2 together stronger or weaker than the bond holding NaCl (salt) together? Answer: The atomic number for nitrogen is 7, and its mass number is 14. The molecular weight of N2 is 28. A triple covalent bond holds N2 together, and a mole of N2 would weigh 28 g. Covalent bonds are stronger than ionic bonds. For example, ionic bonds easily dissolve in water. 91) 92) Draw N2 and CH4 showing the electrons and orbitals involved in the bonds. 92) Answer: 93) Recent evidence shows that ocean temperatures have increased by about one-tenth of a degree over the past fifty years. This doesn't sound like much... why is it considered to be strong evidence for global warming? rise in ocean temperatures is strong evidence for global warming because water has such a high specific heat. It takes a lot of energy to warm all the ocean water even just a tenth of a degree. 93) 16

17 94) Compare and contrast hydrogen bonds and ionic bonds. 94) oth hydrogen bonds and ionic bonds form due to the attraction of opposite charges for each other. However, only partial charges (from unequally shared electrons in covalent bonds) are involved in hydrogen bonds, whereas ions have gained or lost whole electrons. Hydrogen bonds are much weaker than ionic bonds. 17