1 Answers
Trouton's rule states that the entropy of vaporization is almost the same value, about 85–88 J/, for various kinds of liquids at their boiling points. The entropy of vaporization is defined as the ratio between the enthalpy of vaporization and the boiling temperature. It is named after Frederick Thomas Trouton.
It is be expressed as a function of the gas constant R:
A similar way of stating this is that the latent heat is connected to boiling point roughly as
Trouton’s rule can be explained by using Boltzmann's definition of entropy to the relative change in free volume between the liquid and vapour phases. It is valid for many liquids; for instance, the entropy of vaporization of toluene is 87.30 J/, that of benzene is 89.45 J/, and that of chloroform is 87.92 J/. Because of its convenience, the rule is used to estimate the enthalpy of vaporization of liquids whose boiling points are known.