The molar heat of fusion of benzene (C6H6) is 9.92 kJ/mol.

It is possible to balance a paper clip on the surface of water in a beaker. If you add a bit of soap to the water, however, the paper clip sinks. Explain how the paper clip can float and why it sinks when soap is added.

Consider a sealed container half-filled with water. Which statement best describes what occurs in the container? a. Water evaporates until the air is saturated with water vapor; at this point, no more water evaporates. b. Water evaporates until the air is overly saturated (supersaturated) with water, and most of this water recondenses; this cycle continues until a certain amount of water vapor is present, and then the cycle ceases. c. Water does not evaporate because the container is sealed. d. Water evaporates, and then water evaporates and recondenses simultaneously and continuously.e. Water evaporates until it is eventually all in vapor form. Explain each choice. Justify your choice, and for choices you did not pick, explain what is wrong with them

Explain the following: You add 100 mL water to a 500-mL round-bottom flask and heat the water until it is boiling. You remove the heat and stopper the flask, and the boiling stops. You then run cool water over the neck of the flask, and the boiling begins again. It seems as though you are boiling water by cooling it.

Is it possible for the dispersion forces in a particular substance to be stronger than the hydrogen bonding forces in another substance? Explain your answer.

Does the nature of intermolecular forces change when a substance goes from a solid to a liquid, or from a liquid to a gas? What causes a substance to undergo a phase change?

Why do liquids have a vapor pressure? Do all liquids have vapor pressures? Explain. Do solids exhibit vapor pressure? Explain. How does vapor pressure change with changing temperature? Explain

Water in an open beaker evaporates over time. As the water is evaporating, is the vapor pressure increasing, decreasing, or staying the same? Why?

What is the vapor pressure of water at 100C? How do you know?

Refer to Fig. 10.44. Why doesnt temperature increase continuously over time? That is, why does the temperature stay constant for periods of time?

Which are stronger, intermolecular or intramolecular forces for a given molecule? What observation(s) have you made that support this? Explain.

Why does water evaporate?

Rationalize why chalk (calcium carbonate) has a higher melting point than motor oil (large compound made from carbon and hydrogen), which has a higher melting point than water and engages in relatively strong hydrogen bonding interactions.

Why are the dipoledipole interactions between polar molecules not important in the vapor phase?

Hydrogen bonding is a special case of very strong dipoledipole interactions possible among only certain atoms. What atoms in addition to hydrogen are necessary for hydrogen bonding? How does the small size of the hydrogen atom contribute to the unusual strength of the dipoledipole forces involved in hydrogen bonding?

Atoms are assumed to touch in closest packed structures, yet every closest packed unit cell contains a significant amount of empty space. Why?

Define critical temperature and critical pressure. In terms of the kinetic molecular theory, why is it impossible for a substance to exist as a liquid above its critical temperature?

Use the kinetic molecular theory to explain why a liquid gets cooler as it evaporates from an insulated container

Will a crystalline solid or an amorphous solid give a simpler X-ray diffraction pattern? Why?

What is an alloy? Explain the differences in structure between substitutional and interstitial alloys. Give an example of each type

Describe what is meant by a dynamic equilibrium in terms of the vapor pressure of a liquid

How does each of the following affect the rate of evaporation of a liquid in an open dish? a. intermolecular forces b. temperature c. surface area

Explain how the evaporation of water acts as a coolant for the earth

When wet laundry is hung on a clothesline on a cold winter day, it will freeze but eventually dry. Explain

Cake mixes and other packaged foods that require cooking often contain special directions for use at high elevations. Typically these directions indicate that the food should be cooked longer above 5000 ft. Explain why it takes longer to cook something at higher elevations.

You have three covalent compounds with three very different boiling points. All of the compounds have similar molar mass and relative shape. Explain how these three compounds could have very different boiling points

Compare and contrast the structures of the following solids. a. diamond versus graphite b. silica versus silicates versus glass

Compare and contrast the structures of the following solids. a. CO2(s) versus H2O(s) b. NaCl(s) versus CsCl(s); see Exercise 67 for the structures.

Silicon carbide (SiC) is an extremely hard substance that acts as an electrical insulator. Propose a structure for SiC.

How could you tell experimentally if TiO2 is an ionic solid or a network solid?

A common prank on college campuses is to switch the salt and sugar on dining hall tables, which is usually easy because the substances look so much alike. Yet, despite the similarity in their appearance, these two substances differ greatly in their properties, since one is a molecular solid and the other is an ionic solid. How do the properties differ and why?

A plot of ln (Pvap) versus 1/T (K) is linear with a negative slope. Why is this the case?

Iodine, like most substances, exhibits only three phases: solid, liquid, and vapor. The triple point of iodine is at 90 torr and 115C. Which of the following statements concerning liquid I2 must be true? Explain your answer. a. I2(l) is more dense than I2(g). b. I2(l) cannot exist above 115C. c. I2(l) cannot exist at 1 atmosphere pressure. d. I2(l) cannot have a vapor pressure greater than 90 torr. e. I2(l) cannot exist at a pressure of 10 torr.

Identify the most important types of interparticle forces present in the solids of each of the following substances. a. Ar e. CH4 b. HCl f. CO c. HF g. NaNO3 d. CaCl2

Identify the most important types of interparticle forces present in the solids of each of the following substances. a. BaSO4 e. CsI b. H2S f. P4 c. Xe g. NH3 d. C2H6

Predict which substance in each of the following pairs would have the greater intermolecular forces. a. CO2 or OCS b. SeO2 or SO2 c. CH3CH2CH2NH2 or H2NCH2CH2NH2 d. CH3CH3 or H2CO e. CH3OH or H2CO

Consider the compounds Cl2, HCl, F2, NaF, and HF. Which compound has a boiling point closest to that of argon? Explain.

Rationalize the difference in boiling points for each of the following pairs of substances: a. n-pentane CH3CH2CH2CH2CH3 36.2C b. HF 20C HCl 85C c. HCl 85C LiCl 1360C d. n-pentane CH3CH2CH2CH2CH3 36.2C n-hexane CH3CH2CH2CH2CH2CH3 69C 38. C

Consider the following compounds and formulas. (Note: The formulas are written in such a way as to give you an idea of the structure.) ethanol: CH3CH2OH dimethyl ether: CH3OCH3 propane: CH3CH2CH3 The boiling points of these compounds are (in no particular order) 42.1C, 23C, and 78.5C. Match the boiling points to the correct compounds.

In each of the following groups of substances, pick the one that has the given property. Justify your answer. a. highest boiling point: HBr, Kr, or Cl2 b. highest freezing point: H2O, NaCl, or HF c. lowest vapor pressure at 25C: Cl2, Br2, or I2 d. lowest freezing point: N2, CO, or CO2e. lowest boiling point: CH4, CH3CH3, or CH3CH2CH3f. highest boiling point: HF, HCl, or HBrO B g. lowest vapor pressure at 25C: CH3CH2CH3, CH3CCH3, or CH3CH2CH2OH

In each of the following groups of substances, pick the one that has the given property. Justify each answer. a. highest boiling point: CCl4, CF4, CBr4 b. lowest freezing point: LiF, F2, HCl c. smallest vapor pressure at 25C: CH3OCH3, CH3CH2OH, CH3CH2CH3 d. greatest viscosity: H2S, HF, H2O2 e. greatest heat of vaporization: H2CO, CH3CH3, CH4 f. smallest enthalpy of fusion: I2, CsBr, CaO

The shape of the meniscus of water in a glass tube is different from that of mercury in a glass tube. Why?

Explain why water forms into beads on a waxed car finish

Hydrogen peroxide (H2O2) is a syrupy liquid with a relatively low vapor pressure and a normal boiling point of 152.2C. Rationalize the differences of these physical properties from those of water.

Carbon diselenide (CSe2) is a liquid at room temperature. The normal boiling point is 125C, and the melting point is 45.5C. Carbon disulfide (CS2) is also a liquid at room temperature with normal boiling and melting points of 46.5C and 111.6C, respectively. How do the strengths of the intermolecular forces vary from CO2 to CS2 to CSe2? Explain. St

X rays from a copper X-ray tube (  154 pm) were diffracted at an angle of 14.22 degrees by a crystal of silicon. Assuming first-order diffraction (n  1 in the Bragg equation), what is the interplanar spacing in silicon?

The second-order diffraction (n  2) for a gold crystal is at an angle of 22.20 for X rays of 154 pm. What is the spacing between these crystal planes?

A topaz crystal has an interplanar spacing (d ) of 1.36 (1  1 1010 m). Calculate the wavelength of the X ray that should be used if  15.0 (assume n  1).

X rays of wavelength 2.63 were used to analyze a crystal. The angle of first-order diffraction (n  1 in the Bragg equation) was 15.55 degrees. What is the spacing between crystal planes, and what would be the angle for second-order diffraction (n  2)?

Calcium has a cubic closest packed structure as a solid. Assuming that calcium has an atomic radius of 197 pm, calculate the density of solid calcium.

Nickel has a face-centered cubic unit cell. The density of nickel is 6.84 g/cm3 . Calculate a value for the atomic radius of nickel.

A certain form of lead has a cubic closest packed structure with an edge length of 492 pm. Calculate the value of the atomic radius and the density of lead

Iridium (Ir) has a face-centered cubic unit cell with an edge length of 383.3 pm. Calculate the density of solid iridium.

You are given a small bar of an unknown metal X. You find the density of the metal to be 10.5 g/cm3 . An X-ray diffraction experiment measures the edge of the face-centered cubic unit cell as 4.09 (1  1010 m). Identify X.

A metallic solid with atoms in a face-centered cubic unit cell with an edge length of 392 pm has a density of 21.45 g/cm3 . Calculate the atomic mass and the atomic radius of the metal. Identify the metal.

Titanium metal has a body-centered cubic unit cell. The density of titanium is 4.50 g/cm3 . Calculate the edge length of the unit cell and a value for the atomic radius of titanium. (Hint: In a body-centered arrangement of spheres, the spheres touch across the body diagonal.)

Barium has a body-centered cubic structure. If the atomic radius of barium is 222 pm, calculate the density of solid barium.

The radius of gold is 144 pm, and the density is 19.32 g/cm3 . Does elemental gold have a face-centered cubic structure or a body-centered cubic structure?

The radius of tungsten is 137 pm and the density is 19.3 g/cm3 . Does elemental tungsten have a face-centered cubic structure or a body-centered cubic structure?

What fraction of the total volume of a cubic closest packed structure is occupied by atoms? (Hint: .) What fraction of the total volume of a simple cubic structure is occupied by atoms? Compare the answers

Iron has a density of 7.86 g/cm3 and crystallizes in a bodycentered cubic lattice. Show that only 68% of a body-centered lattice is actually occupied by atoms, and determine the atomic radius of iron.

Explain how doping silicon with either phosphorus or gallium increases the electrical conductivity over that of pure silicon.

Explain how a pn junction makes an excellent rectifier

Selenium is a semiconductor used in photocopying machines. What type of semiconductor would be formed if a small amount of indium impurity is added to pure selenium?

The Group 3A/Group 5A semiconductors are composed of equal amounts of atoms from Group 3A and Group 5Afor example, InP and GaAs. These types of semiconductors are used in lightemitting diodes and solid-state lasers. What would you add to make a p-type semiconductor from pure GaAs? How would you dope pure GaAs to make an n-type semiconductor?

The band gap in aluminum phosphide (AlP) is 2.5 electron-volts (1 eV  1.6 1019 J). What wavelength of light is emitted by an AlP diode?

An aluminum antimonide solid-state laser emits light with a wavelength of 730. nm. Calculate the band gap in joules.

The structures of some common crystalline substances are shown below. Show that the net composition of each unit cell corresponds to the correct formula of each substance.

The unit cell for nickel arsenide is shown below. What is the formula of this compound?

Cobalt fluoride crystallizes in a closest packed array of fluoride ions with the cobalt ions filling one-half of the octahedral holes. What is the formula of this compound?

The compounds Na2O, CdS, and ZrI4 all can be described as cubic closest packed anions with the cations in tetrahedral holes. What fraction of the tetrahedral holes is occupied for each case?

What is the formula for the compound that crystallizes with a cubic closest packed array of sulfur ions, and that contains zinc ions in of the tetrahedral holes and aluminum ions in of the octahedral holes?

Assume the two-dimensional structure of an ionic compound, MxAy, is What is the empirical formula of this ionic compound?

A certain metal fluoride crystallizes in such a way that the fluoride ions occupy simple cubic lattice sites, while the metal ions occupy the body centers of half the cubes. What is the formula of the metal fluoride?

The structure of manganese fluoride can be described as a simple cubic array of manganese ions with fluoride ions at the center of each edge of the cubic unit cell. What is the charge of the manganese ions in this compound?

The unit cell of MgO is shown below. Does MgO have a structure like that of NaCl or ZnS? If the density of MgO is 3.58 g/cm3 , estimate the radius (in centimeters) of the O2 anions and the Mg2 cations

In solid KCl the smallest distance between the centers of a potassium ion and a chloride ion is 314 pm. Calculate the length of the edge of the unit cell and the density of KCl, assuming it has the same structure as sodium chloride

The CsCl structure is a simple cubic array of chloride ions with a cesium ion at the center of each cubic array (see Exercise 67). Given that the density of cesium chloride is 3.97 g/cm3 , and assuming that the chloride and cesium ions touch along the body diagonal of the cubic unit cell, calculate the distance between the centers of adjacent Cs and Cl ions in the solid. Compare this value with the expected distance based on the sizes of the ions. The ionic radius of Cs is 169 pm, and the ionic radius of Cl is 181 pm.

MnO has either the NaCl type structure or the CsCl type structure (see Exercise 67). The edge length of the MnO unit cell is 4.47 108 cm and the density of MnO is 5.28 g/cm3 . a. Does MnO crystallize in the NaCl or the CsCl type structure? b. Assuming that the ionic radius of oxygen is 140. pm, estimate the ionic radius of manganese.

What type of solid will each of the following substances form? a. CO2 e. Ru i. NaOH b. SiO2 f. I2 j. U c. Si g. KBr k. CaCO3 d. CH4 h. H2O l. PH3

What type of solid will each of the following substances form? a. diamond e. KCl i. Ar b. PH3 f. quartz j. Cu c. H2 g. NH4NO3 k. C6H12O6 d. Mg h. SF2

The memory metal, nitinol, is an alloy of nickel and titanium. It is called a memory metal because after being deformed, a piece of nitinol wire will return to its original shape. The structure of nitinol consists of a simple cubic array of Ni atoms and an inner penetrating simple cubic array of Ti atoms. In the extended lattice, a Ti atom is found at the center of a cube of Ni atoms; the reverse is also true. a. Describe the unit cell for nitinol. b. What is the empirical formula of nitinol? c. What are the coordination numbers (number of nearest neighbors) of Ni and Ti in nitinol?

Superalloys have been made of nickel and aluminum. The alloy owes its strength to the formation of an ordered phase, called the gamma-prime phase, in which Al atoms are at the corners of a cubic unit cell and Ni atoms are at the face centers. What is the composition (relative numbers of atoms) for this phase of the nickelaluminum superalloy?

Perovskite is a mineral containing calcium, titanium, and oxygen. Two different representations of the unit cell are shown below. Show that both these representations give the same formula and the same number of oxygen atoms around each titanium atom.

A mineral crystallizes in a cubic closest packed array of oxygen ions with aluminum ions in some of the octahedral holes and magnesium ions in some of the tetrahedral holes. Deduce the formula of this mineral and predict the fraction of octahedral holes and tetrahedral holes that are filled by the various cations.

Materials containing the elements Y, Ba, Cu, and O that are superconductors (electrical resistance equals zero) at temperatures above that of liquid nitrogen were recently discovered. The structures of these materials are based on the perovskite structure. Were they to have the ideal perovskite structure, the superconductor would have the structure shown in part (a) of the figure below. a. What is the formula of this ideal perovskite material? b. How is this structure related to the perovskite structure shown in Exercise 83? These materials, however, do not act as superconductors unless they are deficient in oxygen. The structure of the actual superconducting phase appears to be that shown in part (b) of the figure. c. What is the formula of this material?

The structures of another class of ceramic, high-temperature superconductors are shown in the following figure. a. Determine the formula of each of these four superconductors. b. One of the structural features that appears to be essential for high-temperature superconductivity is the presence of planar sheets of copper and oxygen atoms. As the number of sheets in each unit cell increases, the temperature for the onset of superconductivity increases. Order the four structures from lowest to the highest superconducting temperature. c. Assign oxidation states to Cu in each structure assuming Tl exists as Tl3. The oxidation states of Ca, Ba, and O are assumed to be 2, 2, and 2, respectively. d. It also appears that copper must display a mixture of oxidation states for a material to exhibit superconductivity. Explain how this occurs in these materials as well as in the superconductor in Exercise 85.

Plot the following data and determine Hvap for magnesium and lithium. In which metal is the bonding stronger?

From the following data for liquid nitric acid, determine its heat of vaporization and normal boiling point. Temperature (C) Vapor Pressure (mm Hg) 0. 14.4 10. 26.6 20. 47.9 30. 81.3 40. 133 50. 208 80. 670.

In Breckenridge, Colorado, the typical atmospheric pressure is 520. torr. What is the boiling point of water (Hvap  40.7 kJ/mol) in Breckenridge?

The temperature inside a pressure cooker is 115C. Calculate the vapor pressure of water inside the pressure cooker. What would be the temperature inside the pressure cooker if the vapor pressure of water was 3.50 atm?

Carbon tetrachloride, CCl4, has a vapor pressure of 213 torr at 40.C and 836 torr at 80.C. What is the normal boiling point of CCl4?

The normal boiling point for acetone is 56.5C. At an elevation of 5300 ft the atmospheric pressure is 630. torr. What would be the boiling point of acetone (Hvap  32.0 kJ/mol) at this elevation? What would be the vapor pressure of acetone at 25.0C at this elevation?

A substance, X, has the following properties: Sketch a heating curve for substance X starting at 50.C.

Given the data in Exercise 93 on substance X, calculate the energy that must be removed to convert 250. g of substance X from a gas at 100.C to a solid at 50.C. Assume X has a molar mass of 75.0 g/mol.

The molar heat of fusion of sodium metal is 2.60 kJ/mol, whereas its heat of vaporization is 97.0 kJ/mol. a. Why is the heat of vaporization so much larger than the heat of fusion? b. What quantity of heat would be needed to melt 1.00 g sodium at its normal melting point? c. What quantity of heat would be needed to vaporize 1.00 g sodium at its normal boiling point? d. What quantity of heat would be evolved if 1.00 g sodium vapor condensed at its normal boiling point?

The molar heat of fusion of benzene (C6H6) is 9.92 kJ/mol. Its molar heat of vaporization is 30.7 kJ/mol. Calculate the heat required to melt 8.25 g benzene at its normal melting point. Calculate the heat required to vaporize 8.25 g benzene at its normal boiling point. Why is the heat of vaporization more than three times the heat of fusion?

What quantity of energy does it take to convert 0.500 kg ice at 20.C to steam at 250.C? Specific heat capacities: ice, 2.03 J/g  C; liquid, 4.2 J/g  C; steam, 2.0 J/g  C; Hvap  40.7 kJ/mol; Hfus  6.02 kJ/mol. 98.

Consider a 75.0-g sample of H2O(g) at 125C. What phase or phases are present when 215 kJ of energy is removed from this sample? (See Exercise 97.)

An ice cube tray contains enough water at 22.0C to make 18 ice cubes that each have a mass of 30.0 g. The tray is placed in a freezer that uses CF2Cl2 as a refrigerant. The heat of vaporization of CF2Cl2 is 158 J/g. What mass of CF2Cl2 must be vaporized in the refrigeration cycle to convert all the water at 22.0C to ice at 5.0C? The heat capacities for H2O(s) and H2O(l) are 2.03 J/g  C and 4.18 J/g  C, respectively, and the enthalpy of fusion for ice is 6.02 kJ/mol. 100

A 0.250-g chunk of sodium metal is cautiously dropped into a mixture of 50.0 g water and 50.0 g ice, both at 0C. The reaction is Will the ice melt? Assuming the final mixture has a specific heat capacity of 4.18 J/g  C, calculate the final temperature. The enthalpy of fusion for ice is 6.02 kJ/mol.

Consider the phase diagram given below. What phases are present at points A through H? Identify the triple point, normal boiling point, normal freezing point, and critical point. Which phase is denser, solid or liquid?

Sulfur exhibits two solid phases, rhombic and monoclinic. Use the accompanying phase diagram for sulfur to answer the following questions. (The phase diagram is not to scale.) a. How many triple points are in the phase diagram? b. What phases are in equilibrium at each of the triple points? c. What is the stable phase at 1 atm and 100.C? d. What are the normal melting point and the normal boiling point of sulfur? e. Which is the densest phase f. At a pressure of 1.0 105 atm, can rhombic sulfur sublime? g. What phase changes occur when the pressure on a sample of sulfur at 100.C is increased from 1.0 108 atm to 1500 atm? 1

Use the accompanying phase diagram for carbon to answer the following questions. a. How many triple points are in the phase diagram? b. What phases can coexist at each triple point? c. What happens if graphite is subjected to very high pressures at room temperature? d. If we assume that the density increases with an increase in pressure, which is more dense, graphite or diamond?

Like most substances, bromine exists in one of the three typical phases. Br2 has a normal melting point of 7.2C and a normal boiling point of 59C. The triple point for Br2 is 7.3C and 40 torr, and the critical point is 320C and 100 atm. Using this information, sketch a phase diagram for bromine indicating the points described above. Based on your phase diagram, order the three phases from least dense to most dense. What is the stable phase of Br2 at room temperature and 1 atm? Under what temperature conditions can liquid bromine never exist? What phase changes occur as the temperature of a sample of bromine at 0.10 atm is increased from 50C to 200C? 105.

The melting point of a fictional substance X is 225C at 10.0 atm. If the density of the solid phase of X is 2.67 g/cm3 and the density of the liquid phase is 2.78 g/cm3 at 10.0 atm, predict whether the normal melting point of X will be less than, equal to, or greater than 225C. Explain.

Consider the following data for xenon: Triple point: 121C, 280 torr Normal melting point: 112C Normal boiling point: 107C Which is more dense, Xe(s) or Xe(l)? How do the melting point and boiling point of xenon depend on pressure?

Consider two different organic compounds, each with the formula C2H6O. One of these compounds is a liquid at room conditions and the other is a gas. Write Lewis structures consistent with this observation, and explain your answer. (Hint: The oxygen atom in both structures satisfies the octet rule with two bonds and two lone pairs.)

Rationalize the differences in physical properties in terms of intermolecular forces for the following organic compounds. Compare the first three substances with each other, compare the last three with each other, and then compare all six. Can you account for any anomalies? bp (C) mp (C) Hvap (kJ/mol) Benzene, C6H6 80 6 33.9 Naphthalene, C10H8 218 80 51.5 Carbon tetrachloride 76 23 31.8 Acetone, CH3COCH3 56 95 31.8 Acetic acid, CH3CO2H 118 17 39.7 Benzoic acid, C6H5CO2H 249 122 68.2

Oil of wintergreen, or methyl salicylate, has the following structure: Methyl 4-hydroxybenzoate is another molecule with exactly the same molecular formula; it has the following structure: Account for the large difference in the melting points of the two substances.

Amino acids are the building blocks of the bodys worker molecules called proteins. When two amino acids bond together, they do so through the formation of a peptide linkage, and a dipeptide is formed. Consider the following tripeptide formed when three alanine amino acids bond together: What types of interparticle forces could be present in a sample of this tripeptide?

When a person has a severe fever, one therapy used to reduce the fever is an alcohol rub. Explain how the evaporation of alcohol from a persons skin removes heat energy from the body

A common response to hearing that the temperature in New Mexico is 105F is, Its not that bad; its a dry heat, whereas at the same time the summers in Atlanta, Georgia, are characterized as dreadful, even though the air temperature is typically lower. What role does humidity play in how our bodies regulate temperature?

Why is a burn from steam typically much more severe than a burn from boiling water?

Diethyl ether (CH3CH2OCH2CH3) was one of the first chemicals used as an anesthetic. At 34.6C, diethyl ether has a vapor pressure of 760. torr, and at 17.9C, it has a vapor pressure of 400. torr. What is the H of vaporization for diethyl ether?

Some of the physical properties of H2O and D2O are as follows: 118. Consider the following enthalpy changes: How do the strengths of hydrogen bonds vary with the electronegativity of the element to which hydrogen is bonded? Where in the preceding series would you expect hydrogen bonds of the following type to fall? 119. The unit cell for a pure xenon fluoride compound is shown below. What is the formula of the compound? 120. Boron nitride (BN) exists in two forms. The first is a slippery solid formed from the reaction of BCl3 with NH3, followed by heating in an ammonia atmosphere at 750C. Subjecting the first form of BN to a pressure of 85,000 atm at 1800C produces a second form that is the second hardest substance known. Both forms of BN remain solids to 3000C. Suggest structures for the two forms of BN. 121. Consider the following data concerning four different substances. Xenon Fluorine H  21 kJ/mol H2O1g2  HOH1g2 H2O---HOH 1in ice2 H  46 kJ/mol 1CH322CO  HF 1CH322CO---HF F  HF FHF H  155 kJ/mol Property H2O D2O Density at 20C (g/mL) 0.997 1.108 Boiling point (C) 100.00 101.41 Melting point (C) 0.00 3.79 Hvap (kJ/mol) 40.7 41.61 Hfus (kJ/mol) 6.01 6.3 Account for the differences. (Note: D is a symbol often used for 2 H, the deuterium isotope of hydrogen.) 116. R

Rationalize the following boiling points

Consider the following vapor pressure versus temperature plot for three different substances A, B, and C. If the three substances are CH4, SiH4, and NH3, match each curve to the correct substance

Consider the following enthalpy changes: How do the strengths of hydrogen bonds vary with the electronegativity of the element to which hydrogen is bonded? Where in the preceding series would you expect hydrogen bonds of the following type to fall?

The unit cell for a pure xenon fluoride compound is shown below. What is the formula of the compound?

Boron nitride (BN) exists in two forms. The first is a slippery solid formed from the reaction of BCl3 with NH3, followed by heating in an ammonia atmosphere at 750C. Subjecting the first form of BN to a pressure of 85,000 atm at 1800C produces a second form that is the second hardest substance known. Both forms of BN remain solids to 3000C. Suggest structures for the two forms of BN. 1

Consider the following data concerning four different substances

Argon has a cubic closest packed structure as a solid. Assuming that argon has a radius of 190. pm, calculate the density of solid argon

Dry nitrogen gas is bubbled through liquid benzene (C6H6) at 20.0C. From 100.0 L of the gaseous mixture of nitrogen and benzene, 24.7 g benzene is condensed by passing the mixture through a trap at a temperature where nitrogen is gaseous and the vapor pressure of benzene is negligible. What is the vapor pressure of benzene at 20.0C?

A 20.0-g sample of ice at 10.0C is mixed with 100.0 g water at 80.0C. Calculate the final temperature of the mixture assuming no heat loss to the surroundings. The heat capacities of H2O(s) and H2O(l) are 2.03 and 4.18 J/g  C, respectively, and the enthalpy of fusion for ice is 6.02 kJ/mol. 1

In regions with dry climates, evaporative coolers are used to cool air. A typical electric air conditioner is rated at 1.00 104 Btu/h (1 Btu, or British thermal unit  amount of energy to raise the temperature of 1 lb water by 1F). What quantity of water must be evaporated each hour to dissipate as much heat as a typical electric air conditioner?

The critical point of NH3 is 132C and 111 atm, and the critical point of N2 is 147C and 34 atm. Which of these substances cannot be liquefied at room temperature no matter how much pressure is applied? Explain.

When 1 mol benzene is vaporized at a constant pressure of 1.00 atm and at its boiling point of 353.0 K, 30.79 kJ of energy (heat) is absorbed and the volume change is 28.90 L. What are E and H for this process?

You and a friend each synthesize a compound with the formula XeCl2F2. Your compound is a liquid and your friends compound is a gas (at the same conditions of temperature and pressure). Explain how the two compounds with the same formulas can exist in different phases at the same conditions of pressure and temperature

Using the heats of fusion and vaporization for water given in Exercise 97, calculate the change in enthalpy for the sublimation of water: Using the H value given in Exercise 118 and the number of hydrogen bonds formed with each water molecule, estimate what portion of the intermolecular forces in ice can be accounted for by hydrogen bonding

Consider a perfectly insulated and sealed container. Determine the minimum volume of a container such that a gallon of water at 25C will evaporate completely. If the container is a cube, determine the dimensions in feet. Assume the density of water is 0.998 g/cm3

Consider the following melting point data:

Some ionic compounds contain a mixture of different charged cations. For example, wstite is an oxide that contains both Fe2 and Fe3 cations and has a formula of Fe0.950O1.00. Calculate the fraction of iron ions present as Fe3. What fraction of the sites normally occupied by Fe2 must be vacant in this solid?

Some ionic compounds contain a mixture of different charged cations. For example, some titanium oxides contain a mixture of Ti2 and Ti3 ions. Consider a certain oxide of titanium that is 28.31% oxygen by mass and contains a mixture of Ti2 and Ti3 ions. Determine the formula of the compound and the relative numbers of Ti2 and Ti3 ions

Spinel is a mineral that contains 37.9% aluminum, 17.1% magnesium, and 45.0% oxygen, by mass, and has a density of 3.57 g/cm3 . The edge of the cubic unit cell measures 809 pm. How many of each type of ion are present in the unit cell?

Mn crystallizes in the same type of cubic unit cell as Cu. Assuming that the radius of Mn is 5.6% larger than the radius of Cu and the density of copper is 8.96 g/cm3 , calculate the density of Mn.

You are asked to help set up a historical display in the park by stacking some cannonballs next to a Revolutionary War cannon. You are told to stack them by starting with a triangle in which each side is composed of four touching cannonballs. You are to continue stacking them until you have a single ball on the top centered over the middle of the triangular base. a. How many cannonballs do you need? b. What type of closest packing is displayed by the cannonballs? c. The four corners of the pyramid of cannonballs form the corners of what type of regular geometric solid?

Some water is placed in a sealed glass container connected to a vacuum pump (a device used to pump gases from a container), and the pump is turned on. The water appears to boil and then freezes. Explain these changes using the phase diagram for water. What would happen to the ice if the vacuum pump was left on indefinitely?

The molar enthalpy of vaporization of water at 373 K and 1.00 atm is 40.7 kJ/mol. What fraction of this energy is used to change the internal energy of the water, and what fraction is used to do work against the atmosphere? (Hint: Assume that water vapor is an ideal gas.)

For a simple cubic array, solve for the volume of an interior sphere (cubic hole) in terms of the radius of a sphere in the array.

Rubidium chloride has the sodium chloride structure at normal pressures but assumes the cesium chloride structure at high pressures. (See Exercise 67.) What ratio of densities is expected for these two forms? Does this change in structure make sense on the basis of simple models? The ionic radius is 148 pm for Rb and 181 pm for Cl.

A 0.132-mol sample of an unknown semiconducting material with the formula XY has a mass of 19.0 g. The element X has an electron configuration of [Kr]5s 2 4d10. What is this semiconducting material? A small amount of the Y atoms in the semiconductor is replaced with an equivalent amount of atoms with an electron configuration of [Ar]4s 2 3d104p5 . Does this correspond to n-type or p-type doping?

A metal burns in air at 600C under high pressure to form an oxide with formula MO2. This compound is 23.72% oxygen by mass. The distance between touching atoms in a cubic closest packed crystal of this metal is 269.0 pm. What is this metal? What is its density?

One method of preparing elemental mercury involves roasting cinnabar (HgS) in quicklime (CaO) at 600.C followed by condensation of the mercury vapor. Given the heat of vaporization of mercury (296 J/g) and the vapor pressure of mercury at 25.0C (2.56 103 torr), what is the vapor pressure of the condensed mercury at 300.C? How many atoms of mercury are present in the mercury vapor at 300.C if the reaction is conducted in a closed 15.0-L container? Ma

General Zod has sold Lex Luthor what Zod claims to be a new copper-colored form of kryptonite, the only substance that can harm Superman. Lex, not believing in honor among thieves, decided to carry out some tests on the supposed kryptonite. From previous tests, Lex knew that kryptonite is a metal having a specific heat capacity of 0.082 J/g  C, and a density of 9.2 g/cm3 . Lex Luthors first experiment was an attempt to find the specific heat capacity of kryptonite. He dropped a 10 g 3 g sample of the metal into a boiling water bath at a temperature of 100.0C 0.2C. He waited until the metal had reached the bath temperature and then quickly transferred it to 100 g 3 g of water that was contained in a calorimeter at an initial temperature of 25.0C 0.2C. The final temperature of the metal and water was 25.2C. Based on these results, is it possible to distinguish between copper and kryptonite? Explain. When Lex found that his results from the first experiment were inconclusive, he decided to determine the density of the sample. He managed to steal a better balance and determined the mass of another portion of the purported kryptonite to be 4 g 1 g. He dropped this sample into water contained in a 25-mL graduated cylinder and found that it displaced a volume of 0.42 mL 0.02 mL. Is the metal copper or kryptonite? Explain. Lex was finally forced to determine the crystal structure of the metal General Zod had given him. He found that the cubic unit cell contained 4 atoms and had an edge length of 600. pm. Explain how this information enabled Lex to identify the metal as copper or kryptonite. Will Lex be going after Superman with the kryptonite or seeking revenge on General Zod? What improvements could he have made in his experimental techniques to avoid performing the crystal structure determination? 1047