91Ó°ÊÓ

Rank the following compounds in order of increasing vapor pressure at \(298 \mathrm{K}\). (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH} ;\) (b) \(\mathrm{CH}_{3} \mathrm{OCH}_{3}\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{3}\)

Explain the difference between sublimation and evaporation.

Can ice be melted merely by applying pressure? Explain your answer.

What phases of a substance are present (a) at its triple point and (b) at its critical point?

Explain how the solid-liquid line in the phase diagram of water differs in character from the solid-liquid line in the phase diagrams of most other substances, such as \(\mathrm{CO}_{2}\).

Which phase of a substance (gas, liquid, or solid) is most likely to be the stable phase: (a) at low temperatures and high pressures; (b) at high temperatures and low pressures?

Freeze-drying is used to preserve food at low temperature with minimal loss of flavor. Freeze-drying works by freezing the food and then lowering the pressure with a vacuum pump to sublime the ice. Must the pressure be lower than the pressure at the triple point of \(\mathrm{H}_{2} \mathrm{O}\) ? Why or why not?

Solid helium cannot be converted directly into the vapor phase. Does the phase diagram of helium have a triple point?

Consult Figures \(10.26,10.28,\) and 10.29. List the steps you would take to convert a 10.0 -g sample of water at \(25^{\circ} \mathrm{C}\) and 1 atm of pressure to water at its triple point.

Explain why a needle floats on the surface of water but sinks in a container of methanol \(\left(\mathrm{CH}_{3} \mathrm{OH}\right)\).