Answers for Phase Diagram worksheet
1. The phase diagram for benzene should be similar to the one for
carbon dioxide,
Figure 12.8A in the textbook.
2. liquid is the primary phase (with some vapor)
3. Sublimation occurs if the pressure is below the triple point
pressure (0.05 atm)
and the temperature of a solid is raised to reach the gas phase.
4. It starts as a solid and stays solid.
5. It starts as a gas, condenses to a liquid, then freezes to a
solid.
6. 1.00 g / (78.11 g/mol) = 0.0128 mol
7. Heat liquid from room temperature (298 K) to boiling point (353.2 K)
q = CDT = (136 J/K
mol)(0.0128 mol)(353.2 K - 298 K) = 96.1 J
8. Change the liquid to gas at the boiling point
DH = (30.8 kJ/mol)(0.0128
mol) = 0.394 kJ or 394 J
9. Heat the gas from the boiling point to the final temperature
(373 K)
q = CDT = (81.7 J/K
mol)(0.0128 mol)(373 K - 353.2 K) = 20.7 J
10. Total heat to change benzene from 298 K to 373 K
96.1 J + 394 J + 20.7 J = 511 J
11. Melting is not as big a change for the benzene molecules as
vaporization is.
When a solid changes to a liquid, there is still potential energy
holding the molecules in a group.
All the potential energy has to be overcome to separate the molecules
into the gas state.
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last updated: April 26, 2010