Section 11.6-11.7
1. Define phase diagram
2. Draw a label a hydrogen-bonding phase diagram and a non hydrogen-bonding phase diagram. Why is there
a difference?
3. Define triple point
4. Use the phase diagram for methane, CH4, shown in ▼ Figure 11.30 to answer the following questions. (a)
What are the approximate temperature and pressure of the critical point? (b) What are the approximate
temperature and pressure of the triple point? (c) Is methane a solid, liquid, or gas at 1 atm and 0 °C? (d) If
solid methane at 1 atm is heated while the pressure is held constant, will it melt or sublime? (e) If methane
at 1 atm and 0 °C is compressed until a phase change occurs, in which state is the methane when the
compression is complete?
5. Define liquid crystal.
6. Draw the 5 different liquid crystal phases.
7. Define nematic liquid crystal.
8. Define smetic A and smetic C liquid crystals
9. Define cholesteric liquid crystal
10. Which of these substances is most likely to exhibit liquid crystalline behavior?
11. (a) What is the significance of the critical point in a phase diagram? (b) Why does the line that separates the
gas and liquid phases end at the critical point?
12. Referring to Figure 11.28, describe all the phase changes that would occur in each of the following cases:
(a) Water vapor originally at 0.005 atm and -0.5 °C is slowly compressed at constant temperature until the
final pressure is 20 atm. (b) Water originally at 100.0 °C and 0.50 atm is cooled at constant pressure until
the temperature is -10 °C.
13. The phase diagram for neon is
Use the phase diagram to answer the following questions. (a) What is the approximate value of the normal
melting point? (b) Over what pressure range will solid neon sublime? (c) At room temperature (T = 25 °C) can
neon be liquefied by compressing it?
14. The fact that water on Earth can readily be found in all three states (solid, liquid, and gas) is in part a
consequence of the fact that the triple point of water (T = 0.01 °C, P = 0.006 atm) falls within a range of
temperatures and pressures found on Earth. Saturn’s largest moon Titan has a considerable amount of
methane in its atmosphere. The conditions on the surface of Titan are estimated to be P = 1.6 atm and T =
-178 °C. As seen from the phase diagram of methane (Figure 11.30), these conditions are not far from the
triple point of methane, raising the tantalizing possibility that solid, liquid, and gaseous methane can be
found on Titan. (a) In what state would you expect to find methane on the surface of Titan? (b) On moving
upward through the atmosphere the pressure will decrease. If we assume that the temperature does not
change, what phase change would you expect to see as we move away from the surface?
15. In terms of the arrangement and freedom of motion of the molecules, how are the nematic liquid crystalline
phase and an ordinary liquid phase similar? How are they different?
16. The molecules shown in Figure 11.33 possess polar groups (that is, groupings of atoms that give rise to
sizable dipole moments within the molecules). How might the presence of polar groups enhance the
tendency toward liquid crystal formation?
17. For a given substance, the liquid crystalline phase tends to be more viscous than the liquid phase. Why?
18. It often happens that a substance possessing a smectic liquid crystalline phase just above the melting point
passes into a nematic liquid crystalline phase at a higher temperature. Account for this type of behavior.