Why is the triple point of water (ice-liquid-vapor) a better fixed point for establishing a thermometric scale than either the melting point of ice or the boiling point of water?

Short Answer

Expert verified
The triple point of water is a better fixed point for establishing a thermometric scale than the melting point of ice or the boiling point of water because at the triple point, all three phases of water co-exist in equilibrium. This state is well-defined and can be accurately reproduced in a controlled laboratory setting, making it more reliable and accurate. In contrast, the melting and boiling points can be influenced by impurities or atmospheric changes.

Step by step solution

01

Understand the Concepts

A triple point of a substance is the temperature and pressure at which the substance can co-exist in three phases - solid, liquid, and gas. In the case of water, this is 0.01 degrees Celsius at standard pressure. Thermometric scales are established at fixed points, which are physical situations where a simple change can occur.
02

Compare with other Points

Both the melting point of ice and the boiling point of water have been traditionally used as reference points in many thermometric scales. However, these points can be influenced by impurities or atmospheric changes, leading to slight inaccuracies.
03

Explain the advantage of the Triple Point

The triple point of water, however, represents a unique state where all three phases co-exist in equilibrium. The conditions for this state are well-defined and can be reproduced accurately in a controlled laboratory setting, making it more reliable and accurate as a fixed point for establishing a thermometric scale.

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