Problem: Generic phase diagram for a pure substance. The green line is the sublimation curve, the blue line is the melting curve, and the red line is the vapor-pressure curve.Imagine that the pressure on the solid phase in the figure is decreased at constant temperature. If the solid eventually sublimes, what must be true about the temperature?

FREE Expert Solution

We are asked what would be true about temperature if the pressure is decreased and the solid eventually sublimes.

Sublimation is the transition of a substance directly from the solid to the gas phase, without passing through the intermediate liquid phase. 

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Problem Details


Solid phase is at the left of the diagram (low temperature and ranging from low to high pressure). Below the triple point, T, which separates solids, liquids and gases, at low temperature and pressure, sublimation moves solids to gas and deposition moves gas to solid. Above the triple point, at higher pressure and medium temperature, melting moves solids to liquids and freezing moves liquids to solids. The vapor pressure curve increases from the triple point T to the critical point, C, at higher temperature and pressure. Above the critical point, liquid and gas converge to become a super critical fluid. Liquids vaporize across the vapor pressure curve to gas and gases condense across the vapor pressure curve to liquid.


Generic phase diagram for a pure substance. The green line is the sublimation curve, the blue line is the melting curve, and the red line is the vapor-pressure curve.


Imagine that the pressure on the solid phase in the figure is decreased at constant temperature. If the solid eventually sublimes, what must be true about the temperature?

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