1.14 Phase Diagrams

According to this phase diagram of water, what happens when you increase the pressure from 50 kPa to 150 kPa on an ice cube at 0°C?

• The ice cube remains solid.

• The ice cube sublimes.

• The ice cube melts.

For a given sample of carbon dioxide (CO₂) you increase the temperature from –80°C to 0°C and decrease the pressure from 30 atm to 5 atm. On a phase diagram this causes a crossing of both the solid-liquid boundary and the liquid-gas boundary. Which of the following best describes what happens?

• The solid sublimes to gas.

• The gas deposits directly into a solid.

• The gas condenses to liquid and then freezes solid.

• The solid melts to liquid and then vaporizes to gas.