According to Trouton's rule, what is the approximate standard entropy of vaporization for many normal liquids?

Trouton's rule states that the standard entropy of vaporization for many normal liquids is approximately 85 J K−1 mol−1. This rule is based on the observation that despite the differences in intermolecular forces and molecular structures, many substances tend to have similar entropies of vaporization when they change from the liquid phase to the vapor phase.

This approximate value arises because, during the vaporization process, a liquid's molecules gain significant freedom of movement upon transitioning to the gaseous state, which contributes to a substantial increase in entropy. The value of 85 J K−1 mol−1 represents a good average for a wide range of substances, particularly those that exhibit similar physical properties.

It's important to note that while the provided value is an average, there are exceptions depending on molecular structure and interactions; however, for many common liquids, this approximation holds true. This helps in estimating thermodynamic properties and understanding the relationship between entropy and phase changes in physical chemistry.