10.
At a constant temperature, what would you do to cause this substance to change from the
liquid phase to the solid phase?

11.
To change the liquid to a solid at constant temperature, you could increase the
pressure.
Label the sublimation boundary on the phase diagram. Describe what occurs when a
substance sublimes. What is the reverse process of sublimation?

Sublimation is when a solid turns directly to a gas. The reverse process is
deposition, when a gas turns directly to a solid.
Part B – Phase Diagram for Water
Use water’s phase diagram (below right) to answer questions 12-15.
12.
At a pressure of 1 atmosphere, what is the normal
freezing point of water?

13.
What is the normal boiling point of water, at one
atmosphere of pressure?

14.
The normal boiling point of water is 100 °C.
Denver, CO is approximately 5,280 feet above sea
level, which means the normal atmospheric
pressure is less than 1 atm. In Denver, will water
boil at a higher or lower temperature?

15.
The normal freezing point of water is 0 °C.
In Denver, the water will boil at a temperature below the normal boiling point.
Water is an unusual substance because the slope of the boundary between solid and liquid
is negative. What happens to solid water at 0 °C if you increase the pressure?

If you increase the pressure, the solid water will melt to a liquid. Usually a
pressure increase will freeze, not melt the substance.
Part C – Phase Diagram for Carbon Dioxide
Use carbon dioxide’s phase diagram (below right) to answer questions 16-17.
16.
At 1 atmosphere and room temperature (25°C),
would you expect solid carbon dioxide (at -100°C)
to melt to the liquid phase, or sublime to the gas
phase?

17.
Carbon dioxide will sublime to the gas phase
at room temperature.
Some industrial processes require carbon dioxide,
stored in large tanks as a liquid. In terms of
pressure, what must be true of the carbon dioxide
in those tanks?

The tanks must be kept at a pressure of
greater than 5.1 atm, because liquid carbon
dioxide cannot exist below that pressure.