The triple point of a substance is the unique combination of temperature and pressure at which its solid, liquid, and gas phases coexist in perfect equilibrium. At this precise condition, the substance can simultaneously exist in all three states, with no net change between them.
Each substance has its own specific triple point. For example, the triple point of water occurs at 0.01°C and a pressure of 611.657 pascals. It’s a fundamental reference used to define the Kelvin temperature scale.
The triple point is important in:
- Phase diagrams, where it marks the intersection of phase boundaries,
- Thermodynamic studies, helping to understand phase stability,
- Metrology, where it serves as a standard for calibrating thermometers.
Understanding the triple point is crucial in fields such as physical chemistry, materials science, and planetary science, as it reveals how substances behave under extreme or specific environmental conditions.