Phase Diagram . What will happen to ice at 0°C if the pressure decreases from 1 atm to 0.001 atm?
Strategy : Consult the location on the phase diagram of water (Figure 5.20) and find the point that corresponds to the given temperature and pressure conditions.
According to Figure 5.20, when the pressure decreases while the temperature remains constant, we move vertically from 1 atm (760 mm Hg) to 0.001 atm (0.76 mm Hg). During this process we cross the boundary separating the solidphase from the vapor phase. Thus, when the pressure drops to 0.001 atm, ice sublimes and becomes vapor.
