Triple point

Definition

The triple point is the unique set of conditions at which all three phases (solid, liquid, and gas) of a substance coexist in thermodynamic equilibrium. It is characterized by a specific temperature and pressure for each substance.

5 Must Know Facts For Your Next Test

1. Water's triple point occurs at exactly 0.01°C (273.16 K) and 611.657 pascals (0.00604 atm).
2. At the triple point, the substance can change from one phase to another without any change in temperature or pressure.
3. The triple point is used to define the Kelvin temperature scale; specifically, it sets the value for 273.16 K.
4. Each pure substance has its own unique triple point conditions where solid, liquid, and gas phases coexist.
5. Understanding the triple point is crucial for studying phase diagrams and predicting phase changes under different conditions.

Review Questions

• What are the temperature and pressure conditions for the triple point of water?
• Why is the triple point significant in defining the Kelvin temperature scale?
• How does a substance behave at its triple point?

Related terms

Phase Diagram: A graphical representation showing the stability regions of different phases of a substance as a function of temperature and pressure.

Critical Point: The end point of a phase equilibrium curve where distinct liquid and gas phases do not exist.

Thermodynamic Equilibrium: \text{A state when macroscopic properties such as pressure, temperature, and volume remain constant over time in an isolated system.}