Chapter 12

Explain why water drops are spherical in the absence of gravity.

What are the main properties of liquids (in contrast to gases and solids)?

What are the main properties of solids (in contrast to liquids and gases)?

What is the fundamental difference between an amorphous solid and a crystalline solid?

What factors cause transitions between the solid and liquid state? The liquid and gas state?

Describe the relationship between the state of a substance, its temperature, and the strength of its intermolecular forces.

From what kinds of interactions do intermolecular forces originate?

Why are intermolecular forces generally much weaker than bonding forces?

What is the dispersion force? What does the magnitude of the dispersion force depend on? How can you predict the magnitude of the dispersion force for closely related elements or compounds?

What is the dipole-dipole force? How can you predict the presence of dipole- dipole forces in a compound?

How is the polarity of a liquid generally related to its miscibility with water?

What is hydrogen bonding? How can you predict the presence of hydrogen bonding in a compound?

What is surface tension? How does surface tension result from intermolecular forces? How is it related to the strength of intermolecular forces?

What is viscosity? How does viscosity depend on intermolecular forces? What other factors affect viscosity?

What is capillary action? How does it depend on the relative strengths of adhesive and cohesive forces?

Explain what happens in the processes of vaporization and condensation. Why does the rate of vaporization increase with increasing temperature and surface area?

Why is vaporization endothermic? Why is condensation exothermic?

How is the volatility of a substance related to the intermolecular forces present within the substance?

Explain the process of dynamic equilibrium. How is dynamic equilibrium related to vapor pressure?

How is vapor pressure related to temperature? What happens to the vapor pressure of a substance when the temperature is increased? Decreased?

Define the terms boiling point and normal boiling point.

Explain what happens to a substance when it is heated in a closed container to its critical temperature.

What is sublimation? Give a common example of sublimation.

What is fusion? Is fusion exothermic or endothermic? Why?

Determine the kinds of intermolecular forces that are present in each element or compound. MISSED THIS? a. \(\mathrm{N}_{2}\) b. \(\mathrm{NH}_{3}\) c. CO d. \(\mathrm{CCl}_{4}\)

Determine the kinds of intermolecular forces that are present in each element or compound. a. \(\mathrm{Kr}\) b. \(\mathrm{NCl}_{3}\) c. \(\mathrm{SiH}_{4}\) d. HF

Determine the kinds of intermolecular forces that are present in each element or compound. MISSED THIS? a. HCl b. \(\mathrm{H}_{2} \mathrm{O}\) c. \(\mathrm{Br}_{2}\) d. He

Determine the kinds of intermolecular forces that are present in each element or compound. a. \(\mathrm{PH}_{3}\) b. HBr c. \(\mathrm{CH}_{3} \mathrm{OH}\) d. \(\mathrm{I}_{2}\)

Arrange these compounds in order of increasing boiling point. Explain your reasoning. MISSED THIS? a. \(\mathrm{CH}_{4}\) b. \(\mathrm{CH}_{3} \mathrm{CH}_{3}\) c. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Cl}\) d. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\)

Arrange these compounds in order of increasing boiling point. Explain your reasoning. a. \(\mathrm{H}_{2} \mathrm{~S}\) b. \(\mathrm{H}_{2} \mathrm{Se}\) c. \(\mathrm{H}_{2} \mathrm{O}\)

In each pair of compounds, pick the one with the higher boiling point. Explain your reasoning. MISSED THIS? Read Section 12.3; Watch \(\mathrm{KCV} 12.3,\) IWE 12.2 a. \(\mathrm{CH}_{3} \mathrm{OH}\) or \(\mathrm{CH}_{3} \mathrm{SH}\) b. \(\mathrm{CH}_{3} \mathrm{OCH}_{3}\) or \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) c. \(\mathrm{CH}_{4}\) or \(\mathrm{CH}_{3} \mathrm{CH}_{3}\)

In each pair of compounds, pick the one with the higher boiling point. Explain your reasoning. a. \(\mathrm{NH}_{3}\) or \(\mathrm{CH}_{4}\) b. \(\mathrm{CS}_{2}\) or \(\mathrm{CO}_{2}\) c. \(\mathrm{CO}_{2}\) or \(\mathrm{NO}_{2}\)

In each pair of compounds, pick the one with the higher vapor pressure at a given temperature. Explain your reasoning. a. \(\mathrm{CH}_{4}\) or \(\mathrm{CH}_{3} \mathrm{Cl}\) b. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) or \(\mathrm{CH}_{3} \mathrm{OH}\) c. \(\mathrm{CH}_{3} \mathrm{OH}\) or \(\mathrm{H}_{2} \mathrm{CO}\)

Determine whether each pair of compounds forms a homogeneous solution when combined. For those that form homogeneous solutions, indicate the type of forces that are involved. MISSED THIS? a. \(\mathrm{CCl}_{4}\) and \(\mathrm{H}_{2} \mathrm{O}\) b. \(\mathrm{KCl}\) and \(\mathrm{H}_{2} \mathrm{O}\) c. \(\mathrm{Br}_{2}\) and \(\mathrm{CCl}_{4}\) d. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) and \(\mathrm{H}_{2} \mathrm{O}\)

Determine whether each pair of compounds forms a homogeneous solution when combined. For those that form homogeneous solutions, indicate the type of forces that are involved. a. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\) and \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\) b. \(\mathrm{CBr}_{4}\) and \(\mathrm{H}_{2} \mathrm{O}\) c. \(\mathrm{LiNO}_{3}\) and \(\mathrm{H}_{2} \mathrm{O}\) d. \(\mathrm{CH}_{3} \mathrm{OH}\) and \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\)

Which compound would you expect to have greater surface tension: acetone \(\left[\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CO}\right]\) or water \(\left(\mathrm{H}_{2} \mathrm{O}\right)\) ? Explain.

Explain why the viscosity of multigrade motor oils is less temperature- dependent than that of single-grade motor oils.

Which evaporates more quickly: \(55 \mathrm{~mL}\) of water \(\left(\mathrm{H}_{2} \mathrm{O}\right)\) in a beaker or \(55 \mathrm{~mL}\) of acetone \(\left[\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CO}\right]\) in an identical beaker under identical conditions? Is the vapor pressure of the two substances different? Explain.

Calculate the amount of heat required to completely sublime \(50.0 \mathrm{~g}\) of solid dry ice \(\left(\mathrm{CO}_{2}\right)\) at its sublimation temperature. The heat of sublimation for carbon dioxide is \(32.3 \mathrm{~kJ} / \mathrm{mol}\).

Nitrogen has a normal boiling point of \(77.3 \mathrm{~K}\) and a melting point (at 1 atm) of 63.1 K. Its critical temperature is \(126.2 \mathrm{~K}\), and its critical pressure is \(2.55 \times 10^{4}\) torr. It has a triple point at \(63.1 \mathrm{~K}\) and 94.0 torr. Sketch the phase diagram for nitrogen. Does nitrogen have a stable liquid state at 1 atm?

Water has a high boiling point given its relatively low molar mass. Why?

Water is a good solvent for many substances. What is the molecular basis for this property, and why is it significant?

Explain the role of water in moderating Earth's climate.

How is the density of solid water compared to that of liquid water atypical among substances? Why is this significant?

Explain the observed trend in the melting points of the hydrogen halides. $$ \begin{array}{ll} \text { HI } & -50.8^{\circ} \mathrm{C} \\ \mathrm{HBr} & -88.5^{\circ} \mathrm{C} \\ \mathrm{HCl} & -114.8^{\circ} \mathrm{C} \\ \mathrm{HF} & -83.1^{\circ} \mathrm{C} \end{array} $$

Explain the observed trend in the boiling points of these compounds. $$ \begin{array}{ll} \mathrm{H}_{2} \mathrm{Te} & -2{ }^{\circ} \mathrm{C} \\ \mathrm{H}_{2} \mathrm{Se} & -41.5{ }^{\circ} \mathrm{C} \\ \mathrm{H}_{2} \mathrm{~S} & -60.7{ }^{\circ} \mathrm{C} \\ \mathrm{H}_{2} \mathrm{O} & 100^{\circ} \mathrm{C} \end{array} $$

Draw a heating curve (such as the one in Figure 12.36 ) for 1 mole of methanol beginning at \(170 \mathrm{~K}\) and ending at \(350 \mathrm{~K}\). Assume that the values given here are constant over the relevant temperature ranges. $$ \begin{array}{ll} \hline \text { Melting point } & 176 \mathrm{~K} \\ \text { Boiling point } & 338 \mathrm{~K} \\ \Delta \mathrm{H}_{\text {fus }} & 2.2 \mathrm{~kJ} / \mathrm{mol} \\ \Delta \mathrm{H}_{\text {vap }} & 35.2 \mathrm{~kJ} / \mathrm{mol} \\ \mathrm{C}_{\mathrm{s}, \text { solid }} & 105 \mathrm{~J} / \mathrm{K} \\ \mathrm{C}_{\mathrm{s}} \text { , liquid } & 81.3 \mathrm{~J} / \mathrm{mol} \cdot \mathrm{K} \\ \mathrm{C}_{\mathrm{s}, \text { gas }} & 48 \mathrm{~J} / \mathrm{mol} \cdot \mathrm{K} \\ \hline \end{array} $$

Draw a heating curve (such as the one in Figure 12.36 ) for \(1 \mathrm{~mol}\) of benzene beginning at \(0^{\circ} \mathrm{C}\) and ending at \(100^{\circ} \mathrm{C}\). Assume that the values given here are constant over the relevant tempera- ture ranges. $$ \begin{array}{ll} \hline \text { Melting point } & 5.4^{\circ} \mathrm{C} \\ \text { Boiling point } & 80.1^{\circ} \mathrm{C} \\ \Delta \mathrm{H}_{\text {fus }} & 9.9 \mathrm{~kJ} / \mathrm{mol} \\ \Delta H_{\text {vap }} & 30.7 \mathrm{~kJ} / \mathrm{mol} \\ C_{\text {s, solid }} & 118 \mathrm{~J} / \mathrm{mol} \cdot \mathrm{K} \\ \mathrm{C}_{\text {s, liquid }} & 135 \mathrm{~J} / \mathrm{mol} \cdot \mathrm{K} \\ \mathrm{C}_{\mathrm{s}, \text { gas }} & 104 \mathrm{~J} / \mathrm{mol} \cdot \mathrm{K} \\ \hline \end{array} $$

Three \(1.0-\mathrm{L}\) flasks, maintained at \(308 \mathrm{~K},\) are connected to each other with stopcocks. Initially, the stopcocks are closed. One of the flasks contains \(1.0 \mathrm{~atm}\) of \(\mathrm{N}_{2} ;\) the second, \(2.0 \mathrm{~g}\) of \(\mathrm{H}_{2} \mathrm{O} ;\) and the third, \(0.50 \mathrm{~g}\) of ethanol, \(\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}\). The vapor pressure of \(\mathrm{H}_{2} \mathrm{O}\) at \(308 \mathrm{~K}\) is \(42 \mathrm{mmHg},\) and that of ethanol is \(102 \mathrm{mmHg} .\) The stopcocks are then opened and the contents mix freely. What is the pressure?

One prediction of global warming is the melting of global ice, which may result in coastal flooding. A criticism of this prediction is that the melting of icebergs does not increase ocean levels any more than the melting of ice in a glass of water increases the level of liquid in the glass. Is this a valid criticism? Does the melting of an ice cube in a cup of water raise the level of the liquid in the cup? Why or why not? In response to this criticism, scientists have asserted that they are not worried about melting icebergs, but rather the melting of ice sheets that sit on the continent of Antarctica. Would the melting of this ice increase ocean levels? Why or why not?