In the context of gases, what does a compressibility factor (Z) less than 1 indicate?

A compressibility factor (Z) less than 1 indicates that the attractive interactions among gas particles are stronger than the repulsive interactions. In the ideal gas model, gases have Z equal to 1, indicating that real gases behave ideally. However, when Z is less than 1, it suggests that the gas particles are experiencing significant attractive forces that draw them closer together, leading to reduced pressure compared to an ideal gas.

In practical terms, this behavior is often observed at high pressures or low temperatures where intermolecular forces become significant. The attractive forces pull the particles closer, causing the gas to occupy less volume than predicted by the ideal gas law, hence resulting in a compressibility factor less than one.

Understanding this concept is vital in predicting the behavior of gases under different conditions, and it plays an important role in various applications, including gas storage and transport, as well as in processes like liquefaction.