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Phase diagrams
Intermediate
Pressure–temperature maps of solid, liquid and gas regions.
P–T diagrams show regions of solid, liquid and gas separated by lines. Crossing a line changes phase; slopes tell how melting and boiling points shift with pressure.
Water's melting line slopes backward, which helps ice skating.
Phase boundaries are equilibrium lines.
In more detail
A phase diagram shows which phase of a substance is stable at each combination of temperature and pressure. Boundaries between regions mark phase transitions.
Real-world uses
- Engineers use phase diagrams to choose operating conditions for refrigerants.
- Geologists use them to understand how rocks melt under pressure.
- Engineers use phase diagrams to choose the pressure and temperature at which a refrigerant boils or condenses.
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Frequently asked questions
What is a phase boundary?
A line where two phases coexist in equilibrium.
Why does water have a strange diagram?
Its solid phase is less dense than liquid, so the melting line slopes slightly to the left.
What does the phase boundary show?
The conditions at which two phases, such as solid and liquid, can exist in equilibrium.
Related topics in Heat & Thermodynamics
Molar heat capacity · Latent heat · Calorimetry · Triple and critical points · Conduction · Thermal resistance