Trouton's Rule is an empirical relation stating that the entropy of vaporization ($\Delta S_{vap}=\frac{\Delta H_{vap}}{T_b}$) is roughly constant for many normal liquids at their boiling point.

• Value: $\approx 88{\text{ J K}}^{-1}{\text{ mol}}^{-1}$ (or about $10.5R$).
• This signifies that the change in molecular disorder when moving from a liquid to a gas phase is similar for most substances.
• Exceptions occur for liquids with strong intermolecular forces (hydrogen bonding) like water or HF, which have higher values.