The triple point of air-free water is defined as 273.16 K....

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Key Concepts

Triple Point

The triple point is the unique set of conditions (temperature and pressure) where all three phases of a substance (solid, liquid, and vapor) coexist in thermodynamic equilibrium. This fixed point serves as a standard reference in calibrating thermometers and other precision temperature measurements, highlighting its fundamental role in thermodynamics.

Impurity Effects in Phase Transitions

Impurities, such as dissolved gases, can disrupt the delicate balance required for phase transitions. In the case of water, the presence of air can alter the equilibrium conditions, causing deviations from the true triple point. Removing air ensures that only intrinsic properties of pure water affect the phase boundaries, which is crucial for maintaining accuracy in temperature standards.

Role of Dissolved Gases

Dissolved gases materially affect the physical behavior of liquids. In water, dissolved air can lead to changes in properties such as the melting and boiling points due to effects like bubble formation and pressure changes. Ensuring the water is free of air eliminates these variables, providing a consistent and reproducible reference point necessary for precise scientific measurements.

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