Chapter 13

What intermolecular force(s) must be overcome to (a) Melt ice? (b) Sublime solid \(I_{2} ?\) (c) Convert liquid \(\mathrm{NH}_{3}\) to \(\mathrm{NH}_{3}\) vapor?

What type of forces must be overcome within the solid \(\mathrm{I}_{2}\) when \(I_{2}\) dissolves in methanol, \(\mathrm{CH}_{3} \mathrm{OH}\) ? What type of forces must be disrupted between \(\mathrm{CH}_{3} \mathrm{OH}\) molecules when I \(_{2}\) dissolves? What type of forces exist between \(I_{2}\) and CH \(_{3}\) OH molecules in solution?

What type of intermolecular force must be overcome in converting each of the following from a liquid to a gas? (a) liquid \(\mathrm{O}_{2}\) (b) mercury (c) \(\mathrm{CH}_{3} \mathrm{I}\) (methyl iodide) (d) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) (ethanol)

What type of intermolecular forces must be overcome in converting each of the following from a liquid to a gas? (a) \(\mathrm{CO}_{2}\) (b) \(\mathrm{NH}_{3}\) (c) \(\mathrm{CHCl}_{3}\) (d) \(\mathrm{CCl}_{4}\)

Rank the following atoms or molecules in order of increasing strength of intermolecular forces in the pure substance. Which exist as gases at \(25^{\circ} \mathrm{C}\) and 1 atm? (a) Ne (b) \(\mathrm{CH}_{4}\) (c) CO (d) \(\mathrm{CCl}_{4}\)

Rank the following in order of increasing strength of intermolecular forces in the pure substances. Which exist as gases at \(25^{\circ} \mathrm{C}\) and 1 atm? (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\) (butane) (b) \(\mathrm{CH}_{3} \mathrm{OH}\) (methanol) (c) He

Which of the following compounds would be expected to form intermolecular hydrogen bonds in the liquid state? (a) \(\mathrm{CH}_{3} \mathrm{OCH}_{3}\) (dimethyl ether) (b) \(\mathrm{CH}_{4}\) (c) HF (d) \(\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}\) (acetic acid) (e) \(\mathrm{Br}_{2}\) (f) \(\mathrm{CH}_{3} \mathrm{OH}\) (methanol)

Which of the following compounds would be expected to form intermolecular hydrogen bonds in the liquid state? (a) \(\mathrm{H}_{2} \mathrm{Se}\) (b) \(\mathrm{HCO}_{2} \mathrm{H}\) (formic acid) (c) HI (d) acetone

In each pair of ionic compounds, which is more likely to have the greater heat of hydration? Briefly explain your reasoning in each case. (a) LiCl or CsCl (b) \(\mathrm{NaNO}_{3}\) or \(\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}\) (c) RbCl or \(\mathrm{NiCl}_{2}\)

When salts of \(\mathrm{Mg}^{2+}, \mathrm{Na}^{+},\) and \(\mathrm{Cs}^{+}\) are placed in water, the positive ion is hydrated (as is the negative ion). Which of these three cations is most strongly hydrated? Which one is least strongly hydrated?

Ethanol, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH},\) has a vapor pressure of \(59 \mathrm{mm} \mathrm{Hg}\) at \(25^{\circ} \mathrm{C} .\) What quantity of heat energy is required to evaporate \(125 \mathrm{mL}\) of the alcohol at \(25^{\circ} \mathrm{C}\) ? The enthalpy of vaporization of the alcohol at \(25^{\circ} \mathrm{C}\) is \(42.32 \mathrm{kJ} / \mathrm{mol} .\) The density of the liquid is \(0.7849 \mathrm{g} / \mathrm{mL}\).

The enthalpy of vaporization of liquid mercury is \(59.11 \mathrm{kJ} / \mathrm{mol} .\) What quantity of heat is required to vaporize \(0.500 \mathrm{mL}\) of mercury at \(357^{\circ} \mathrm{C},\) its normal boiling point? The density of mercury is \(13.6 \mathrm{g} / \mathrm{mL}\)

Which member of each of the following pairs of compounds has the higher boiling point? (a) \(\mathrm{O}_{2}\) or \(\mathrm{N}_{2}\) (b) \(\mathrm{SO}_{2}\) or \(\mathrm{CO}_{2}\) (c) HF or HI (d) \(\mathrm{SiH}_{4}\) or \(\mathrm{GeH}_{4}\)

Place the following four compounds in order of increasing boiling point. (a) \(\mathrm{SCl}_{2}\) (b) \(\mathrm{NH}_{3}\) (c) \(\mathrm{CH}_{4}\) (d) CO

Answer each of the following questions with increases, decreases, or does not change. (a) If the intermolecular forces in a liquid increase, the normal boiling point of the liquid ____. (b) If the intermolecular forces in a liquid decrease, the vapor pressure of the liquid ____. (c) If the surface area of a liquid decreases, the vapor pressure ____. (d) If the temperature of a liquid increases, the equilibrium vapor pressure ____.

Benzene, \(\mathrm{C}_{6} \mathrm{H}_{6}\), is an organic liquid that freezes at \(5.5^{\circ} \mathrm{C}\) (see Figure \(13.1)\) to form beautiful, feather-like crystals. How much heat is evolved when 15.5 g of benzene freezes at \(5.5^{\circ} \mathrm{C} ?\) (The heat of fusion of benzene is \(9.95 \mathrm{kJ} / \mathrm{mol}\).) If the 15.5 -g sample is remelted, again at \(5.5^{\circ} \mathrm{C},\) what quantity of heat is required to convert it to a liquid?

The specific heat capacity of silver is \(0.235 \mathrm{J} / \mathrm{g} \cdot \mathrm{K}\). Its melting point is \(962^{\circ} \mathrm{C},\) and its heat of fusion is \(11.3 \mathrm{kJ} / \mathrm{mol}\) What quantity of heat, in joules, is required to change \(5.00 \mathrm{g}\) of silver from a solid at \(25^{\circ} \mathrm{C}\) to a liquid at \(962^{\circ} \mathrm{C} ?\)

Liquid ammonia, \(\mathrm{NH}_{3}(\ell),\) was once used in home refrigerators as the heat transfer fluid. The specific heat of the liquid is \(4.7 \mathrm{J} / \mathrm{g} \cdot \mathrm{K}\) and that of the vapor is \(2.2 \mathrm{J} / \mathrm{g} \cdot \mathrm{K}\). The enthalpy of vaporization is \(23.33 \mathrm{kJ} / \mathrm{mol}\) at the boiling point. If you heat \(12 \mathrm{kg}\) of liquid ammonia from \(-50.0^{\circ} \mathrm{C}\) to its boiling point of \(-33.3^{\circ} \mathrm{C},\) allow it to evaporate, and then continue warming to \(0.0^{\circ} \mathrm{C}\), how much heat energy must you supply?

If your air conditioner is more than several years old, it may use the chlorofluorocarbon \(\mathrm{CCl}_{2} \mathrm{F}_{2}\) as the heat transfer fluid. The normal boiling point of \(\mathrm{CCl}_{2} \mathrm{F}_{2}\) is \(-29.8^{\circ} \mathrm{C}\) and the enthalpy of vaporization is \(20.11 \mathrm{kJ} / \mathrm{mol}\). The gas and the liquid have specific heats of \(117.2 \mathrm{J} / \mathrm{mol} \cdot \mathrm{K}\) and \(72.3 \mathrm{J} / \mathrm{mol} \cdot \mathrm{K},\) respectively. How much heat is evolved when \(20.0 \mathrm{g}\) of \(\mathrm{CCl}_{2} \mathrm{F}_{2}\) is cooled from \(+40^{\circ} \mathrm{C}\) to \(-40^{\circ} \mathrm{C} ?\)

The critical temperature and pressure of chloromethane are \(416 \mathrm{K}\) and 66.1 atm, respectively. (Chloromethane's triple point is at \(175.4 \mathrm{K} \text { and } 0.0086 \text { atm. })\) Can \(\mathrm{CH}_{3} \mathrm{Cl}\) be liquefied at or above room temperature? Explain briefly.

Methane (CH \(_{4}\) ) cannot be liquefied at room temperature, no matter how high the pressure. Propane \(\left(\mathrm{C}_{3} \mathrm{H}_{8}\right),\) another alkane, has a critical pressure of 41.8 atm and a critical temperature of \(369.9 \mathrm{K}\). (The triple point for propane is at \(85 \mathrm{K}\) and \(1.7 \times 10^{-9}\) atm.) Can propane be liquefied at room temperature?

Rank the following substances in order of increasing strength of intermolecular forces: Ar, \(\mathrm{CH}_{3} \mathrm{OH}, \mathrm{CO}_{2}\)

What types of intermolecular forces are important in the liquid phase of (a) \(\mathrm{C}_{2} \mathrm{H}_{6}\) and (b) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHOH} ?\)

Construct a phase diagram for \(\mathrm{O}_{2}\) from the following information: normal boiling point, \(90.18 \mathrm{K} ;\) normal melting point, \(54.8 \mathrm{K} ;\) and triple point, \(54.34 \mathrm{K}\) at a pressure of 2 mm Hg. Very roughly estimate the vapor pressure of liquid \(\mathrm{O}_{2}\) at \(-196^{\circ} \mathrm{C}\), the lowest temperature easily reached in the laboratory. Is the density of liquid \(\mathbf{O}_{2}\) greater or less than that of solid \(\mathrm{O}_{2} ?\)

If you place \(1.0 \mathrm{L}\) of ethanol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)\) in a room that is \(3.0 \mathrm{m}\) long, \(2.5 \mathrm{m}\) wide, and \(2.5 \mathrm{m}\) high, will all of the alcohol evaporate? If some liquid remains, how much will there be? The vapor pressure of ethanol at \(25^{\circ} \mathrm{C}\) is \(59 \mathrm{mm} \mathrm{Hg},\) and the density of the liquid at this temperature is \(0.785 \mathrm{g} / \mathrm{cm}^{3}\)

Select the substance in each of the following pairs that should have the higher boiling point. (a) \(\mathrm{Br}_{2}\) or \(\mathrm{ICl}\) (b) neon or krypton (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) (ethanol) or \(\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O}\) (ethylene oxide, structure below)

Which salt, \(\mathrm{Li}_{2} \mathrm{SO}_{4}\) or \(\mathrm{Cs}_{2} \mathrm{SO}_{4}\), is expected to have the more exothermic enthalpy of hydration?

In which salts does the cation bind most strongly to water molecules? In which is the binding less strong in comparison? Explain your reasoning. (a) \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{3}\) (b) \(\mathrm{CoCl}_{2}\) (c) \(\mathrm{NaCl}\) (d) \(\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}\)

Silver crystallizes in a face-centered cubic unit cell. Each side of the unit cell has a length of 409 pm. What is the radius of a silver atom? (Hint: Assume the atoms just touch each other on the diagonal across the face of the unit cell. That is, each face atom is touching the four corner atoms.)

Rank the following molecules in order of increasing intermolecular forces: \(\mathrm{CH}_{3} \mathrm{Cl}, \mathrm{HCO}_{2} \mathrm{H}\) (formic acid), and \(\mathrm{CO}_{2}\)

Rank the following compounds in order of increasing molar enthalpy of vaporization: \(\mathrm{CH}_{3} \mathrm{OH}, \mathrm{C}_{2} \mathrm{H}_{6}, \mathrm{HCl}\)

Calcium metal crystallizes in a face-centered cubic unit cell. The density of the solid is \(1.54 \mathrm{g} / \mathrm{cm}^{3} .\) What is the radius of a calcium atom? (IMAGE NOT COPY)

The very dense metal iridium has a face-centered cubic unit cell and a density of \(22.56 \mathrm{g} / \mathrm{cm}^{3} .\) Use this information to calculate the radius of an atom of the element.

The density of copper metal is \(8.95 \mathrm{g} / \mathrm{cm}^{3} .\) If the radius of a copper atom is \(127.8 \mathrm{pm},\) is the copper unit cell simple cubic, body-centered cubic, or face-centered cubic?

The density of copper metal is \(8.95 \mathrm{g} / \mathrm{cm}^{3} .\) If the radius of a copper atom is \(127.8 \mathrm{pm},\) is the copper unit cell simple cubic, body-centered cubic, or face-centered cubic?

Iron has a body-centered cubic unit cell with a cell dimension of \(286.65 \mathrm{pm} .\) The density of iron is \(7.874 \mathrm{g} / \mathrm{cm}^{3} .\) Use this information to calculate Avogadro's number.

Calcium fluoride is the well-known mineral fluorite. It is known that each unit cell contains four \(\mathrm{Ca}^{2+}\) ions and eight \(F^{-}\) ions and that the \(C a^{2+}\) ions are arranged in a fcc lattice. The \(\mathrm{F}^{-}\) ions fill all the tetrahedral holes in a facecentered cubic lattice of \(\mathrm{Ca}^{2+}\) ions. The edge of the \(\mathrm{CaF}_{2}\) unit cell is \(5.46295 \times 10^{-8} \mathrm{cm}\) in length. The density of the solid is \(3.1805 \mathrm{g} / \mathrm{cm}^{3} .\) Use this information to calculate Avogadro's number.

Assuming that in a simple cubic unit cell the spherical atoms or ions just touch along the cube's edges, calculate the percentage of empty space within the unit cell. (Recall that the volume of a sphere is \((4 / 3) \pi r^{3},\) where \(r\) is the radius of the sphere.) (IMAGE NOT COPY)

Acetone, \(\mathrm{CH}_{3} \mathrm{COCH}_{3},\) is a common laboratory solvent. It is usually contaminated with water, however. Why does acetone absorb water so readily? Draw molecular structures showing how water and acetone can interact. What intermolecular force(s) is (are) involved in the interaction?

Cooking oil is not miscible with water. From this observation, what conclusions can you draw regarding the polarity or hydrogen-bonding ability of molecules found in cooking oil?

Liquid ethylene glycol, HOCH \(_{2} \mathrm{CH}_{2} \mathrm{OH}\), is one of the main ingredients in commercial antifreeze. Do you predict its viscosity to be greater or less than that of ethanol, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH} ?\)

Liquid methanol, \(\mathrm{CH}_{3} \mathrm{OH}\), is placed in a glass tube. Predict whether the meniscus of the liquid is concave or convex.

Account for these facts: (a) Although ethanol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)\left(\mathrm{bp}, 80^{\circ} \mathrm{C}\right)\) has a higher molar mass than water \(\left(\mathrm{bp}, 100^{\circ} \mathrm{C}\right),\) the alcohol has a lower boiling point. (b) Mixing 50 mL of ethanol with 50 mL of water produces a solution with a volume slightly less than \(100 \mathrm{mL}\)

Rationalize the observation that \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) 1-propanol, has a boiling point of \(97.2^{\circ} \mathrm{C},\) whereas a compound with the same empirical formula, methyl ethyl ether \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OCH}_{3}\right)\) boils at \(7.4^{\circ} \mathrm{C}\).

During thunderstorms in the Midwest, very large hailstones can fall from the sky. (Some are the size of golf balls!) To preserve some of these stones, we put them in the freezer compartment of a frost-free refrigerator. Our friend, who is a chemistry student, tells us to use an older model that is not frost- free. Why?

A "hand boiler" can be purchased in toy stores or at science supply companies. If you cup your hand around the bottom bulb, the volatile liquid in the boiler boils and the liquid moves to the upper chamber. Using your knowledge of kinetic-molecular theory and intermolecular forces, explain how the hand boiler works. (IMAGE NOT COPY)

A fluorocarbon, \(\mathrm{CF}_{4},\) has a critical temperature of \(-45.7^{\circ} \mathrm{C},\) a critical pressure of \(37 \mathrm{atm},\) and a normal boiling point of \(-128^{\circ} \mathrm{C}\). Are there any conditions under which this compound can be a liquid at room temperature? Explain briefly.

Two identical swimming pools are filled with uniform spheres of ice packed as closely as possible. The spheres in the first pool are the size of grains of sand; those in the second pool are the size of oranges. The ice in both pools melts. In which pool, if either, will the water level be higher? (Ignore any differences in filling space at the planes next to the walls and bottom.)

Acetaminophen is used in analgesics. (A model is in Organic: Alcohols.) (a) Draw the structure of acetaminophen. (b) Is the molecule capable of hydrogen bonding? If so, what are the sites of hydrogen bonding?