3. Over time, an ice cube left in the freezer gradually shrinks without melting. a. During this process, the ice changes directly from a b. Which phase change is this associated with? i. Melting ii. Freezing iii. Boiling iv. Condensing v. Sublimation vi. Deposition to a

8.45 Describe how interactions between molecules affect the vapor pressure of a liquid.

The phase diagram for water over a relative narrow pressure and temperature range is given in Figure 9.19. A phase diagram over a considerably wider range of temperature and pressure (kbar) is given nearby. This phase diagram illustrates the polymorphism of ice, the existence of a solid in more than one form. In this case, Roman numerals are used to designate each polymorphic form. For example, Ice I, ordinary ice, is the form that exists under ordinary pressures. The other forms exist only at higher pressures, in some cases extremely high pressure such as Ice VII and Ice VIII. Using the phase diagram, give the approximate P and T conditions at the triple point for Ice III, Ice V, and liquid water. Determine the approximate temperature and pressure for the triple point for Ices VI, VII, and VIII. What is anomalously different about the fusion curves for Ice VI and Ice VII compared to that of Ice I? What phases exist at 8 kbar and 20 °C? At a constant temperature of −10 °C, start at 3 kbar and increase the pressure to 7 kbar. Identify all the phase changes that occur sequentially as these conditions change. Explain why there is no triple point for the combination of Ice VII, Ice VIII, and liquid water.

Explain why evaporation leads to cooling of the liquid.

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.

8.36 Why are dispersion forces attractive?

8.87 Use the vapor pressure curves illustrated here to answer the questions that follow. (a) What is the vapor pressure of ethanol (C2H5OH) at 60°C? (b) Considering only carbon disulfide (CS2) and ethanol, which has the stranger intermolecular forces in the liquid state? (c) At what temperature does heptane (C7H16) have a vapor pressure of 500 mm Hg? (d) What are the approximate normal boiling pains of each of the three substances? (e) At a pressure of 400 mm Hg and a temperature of 70°C, is each substance a liquid, a gas, or a mixture of liquid and gas?

If you've ever opened a bottle of rubbing alcohol or other solvent on a warm day, you may have heard a little “whoosh” as the vapor that had built up above the liquid escapes. Describe on a microscopic basis how a vapor pressure builds up in a closed container above a liquid. What processes in the container give rise to this phenomenon?

Equilibrium vapor pressures of benzene, C6H6, at various temperatures are given in the table. (a) What is the normal boiling point of benzene? (b) Plot these data so that you have a graph resembling the one in Figure 11.12. At what temperature does the liquid have an equilibrium vapor pressure of 250 mm Hg? At what temperature is the vapor pressure 650 mm Hg? (c) Calculate the molar enthalpy of vaporization for benzene using the ClausiusClapeyron equation.

8.48 Why must the vapor pressure of a substance be measured only after dynamic equilibrium is established?