Phase diagram

Definition

A phase diagram is a graphical representation that shows the conditions of temperature and pressure under which distinct phases (solid, liquid, gas) of a substance exist. It illustrates the equilibrium between different states of matter.

5 Must Know Facts For Your Next Test

1. The triple point on a phase diagram represents the unique set of conditions where all three phases (solid, liquid, gas) coexist in equilibrium.
2. The critical point marks the end of the phase boundary between liquid and gas; beyond this point, there is no distinction between these two phases.
3. Phase diagrams typically include lines known as 'phase boundaries' that delineate transitions between different states of matter.
4. The slope of the solid-liquid boundary can indicate whether a substance expands or contracts upon freezing; for water, this slope is negative.
5. Phase diagrams can be used to predict the state of a substance at any given temperature and pressure by locating that point within the diagram.

Review Questions

• What does the triple point on a phase diagram represent?
• How does the critical point differ from other points on a phase diagram?
• Why is it significant if the solid-liquid boundary has a negative slope?

Related terms

Triple Point:

The specific temperature and pressure at which all three phases (solid, liquid, gas) of a substance coexist in equilibrium.

Critical Point:

The end point of the phase equilibrium curve between liquid and gas, beyond which there is no distinction between these two phases.

Phase Boundary:

Lines on a phase diagram that separate different states of matter and indicate where phase transitions occur.