Chapter 11

Why are the intermolecular attractive forces stronger in liquids and solids than they are in gases?

Compare the behavior of gases, liquids, and solids when they are transferred from one container to another.

For a given substance, how do the intermolecular attractive forces compare in its gaseous, liquid, and solid states?

Why do intermolecular attractions weaken as the distances between the molecules increase?

What are London forces? How are they affected by the sizes of the atoms in a molecule? How are they affected by the number of atoms in a molecule? How are they affected by the shape of a molecule?

Define polarizability. How does this property affect the strengths of London forces?

Describe dipole-dipole attractions.

How do the strengths of covalent bonds and dipoledipole attractions compare? How do the strengths of ordinary dipole-dipole attractions compare with the strengths of hydrogen bonds?

Which would give a stronger ion-dipole interaction with water molecules: \(\mathrm{Al}^{3+}\) or \(\mathrm{Na}^{+}\)

Which kinds of attractive forces, intermolecular or intramolecular, are responsible for chemical properties? Which kinds are responsible for physical properties?

Which is expected to have the higher boiling point, \(\mathrm{C}_{8} \mathrm{H}_{18}\) or \(\mathrm{C}_{4} \mathrm{H}_{10}\) ? Explain your choice.

Ethanol and dimethyl ether have the same molecular formula, \(\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}\). Ethanol boils at \(78.4^{\circ} \mathrm{C}\), whereas dimethyl ether boils at \(-23.7^{\circ} \mathrm{C}\). Their structural formulas are $$ \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH} \quad \mathrm{CH}_{3} \mathrm{OCH}_{3} $$ ethanol \(\quad\) dimethyl ether Explain why the boiling point of the ether is so much lower than the boiling point of ethanol.

What is compressibility? Which is the easiest to compress: solids, liquids, or gases? Why?

What is diffusion? Give an example of diffusion in everyday life.

Why does diffusion occur more slowly in liquids than in gases? Why does diffusion occur extremely slowly in solids?

On the basis of kinetic theory, would you expect the rate of diffusion in a liquid to increase or decrease as the temperature is increased? Explain your answer.

What is surface tension? Why do molecules at the surface of a liquid behave differently from those within the interior?

Which liquid is expected to have the larger surface tension at a given temperature, \(\mathrm{CCl}_{4}\) or \(\mathrm{H}_{2} \mathrm{O}\) ? Explain your answer.

What does wetting of a surface mean? What is a surfactant? What is its purpose and how does it function?

On the basis of what happens on the molecular level, why does evaporation lower the temperature of a liquid?

On the basis of the distribution of kinetic energies of the molecules of a liquid, explain why increasing the liquid's temperature increases the rate of evaporation.

How is the rate of evaporation of a liquid affected by increasing the surface area of the liquid? How is the rate of evaporation affected by the strengths of intermolecular attractive forces?

During the cold winter months, snow often disappears gradually without melting. How is this possible? What is the name of the process responsible for this phenomenon?

What terms do we use to describe the following changes of state? (a) solid \(\rightarrow\) gas, (b) gas \(\rightarrow\) solid, (c) liquid \(\rightarrow\) gas, (d) gas \(\rightarrow\) liquid, (e) solid \(\rightarrow\) liquid, (f) liquid \(\rightarrow\) solid

When a molecule escapes from the surface of a liquid by evaporation, it has a kinetic energy that's much larger than the average \(\mathrm{KE}\). Why is it likely that after being in the vapor for a while its kinetic energy will be much less? If this molecule collides with the surface of the liquid, is it likely to bounce out again?

Why does a molecule of a vapor that collides with the surface of a liquid tend to be captured by the liquid, even if the incoming molecule has a large kinetic energy?

When equilibrium is established in the evaporation of a liquid into a sealed container, we refer to it as a dynamic equilibrium. Why?

Viewed at the molecular level, what is happening when a dynamic equilibrium is established between the liquid and solid forms of a substance? What is the temperature called when a liquid and a solid are in equilibrium?

Is it possible to establish a state of equilibrium between a solid and its vapor? Explain.

Define equilibrium vapor pressure. Why do we call the equilibrium involved a dynamic equilibrium?

Why doesn't a change in the surface area of a liquid cause a change in the equilibrium vapor pressure?

What effect does increasing the temperature have on the equilibrium vapor pressure of a liquid? Why?

Why does moisture condense on the outside of a cool glass of water in the summertime?

Why does moisture condense on the outside of a cool glass of water in the summertime?

Define boiling point and normal boiling point.

Why does the boiling point vary with atmospheric pressure?

When liquid ethanol begins to boil, what is present inside the bubbles that form?

Would the "heat of condensation," \(\Delta H_{\text {condensation }}\), be exothermic or endothermic?

Ethanol (grain alcohol) has a molar heat of vaporiza tion of \(39.3 \mathrm{~kJ} / \mathrm{mol}\). Ethyl acetate, a common solvent. has a molar heat of vaporization of \(32.5 \mathrm{~kJ} / \mathrm{mol}\). Which of these substances has the stronger intermolecular attractions?

Arrange the following substances in order of their increasing values of \(\Delta H_{\text {vaporization }}: \mathrm{HF}, \mathrm{CH}_{4}, \mathrm{CF}_{4}, \mathrm{HCl}\).

For most substances, the solid is more dense than the liquid. Use Le Châtelier's principle to explain why the melting point of such substances should increase with increasing pressure. Sketch the phase diagram for such a substance, being sure to have the solid-liquid equilibrium line slope in the correct direction.

Define critical temperature and critical pressure.

What is a supercritical fluid? Why is supercritical \(\mathrm{CO}_{2}\) used to decaffeinate coffee?

What phases of a substance are in equilibrium at the triple point?

At room temperature, hydrogen can be compressed to very high pressures without liquefying. On the other hand, butane becomes a liquid at high pressure (at room temperature). What does this tell us about the critical temperatures of hydrogen and butane?

Sketch a generic phase diagram that shows the regions where liquids, solids, and gases exist, the lines indicating equilibria between different phases, and the triple point.

Use Le Châtelier's principle to predict the effect of adding heat in the equilibrium: solid \(+\) heat \(\rightleftharpoons\) liquid.

According to the Clausius-Clapeyron equation, how does the vapor pressure of a substance change as the temperature increases?

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

What relationship is there between a crystal lattice and its unit cell?