Latent heat–boiling point relation: Which named relation links the latent heat of vaporization to the normal boiling point for many non-associating liquids?

Introduction / Context:Trouton’s rule states that the entropy of vaporization at the normal boiling point of many non-associating liquids is approximately constant, about 85–88 J/mol·K. This empirical regularity provides a simple link between latent heat and boiling point via ΔHvap ≈ Tb * ΔSvap.

Given Data / Assumptions:

• Liquid is non-associating (no strong hydrogen bonding).
• Property evaluated at the normal boiling point.
• Use as an estimate, not an exact law.

Concept / Approach:Because ΔSvap at Tb is roughly constant for many liquids, ΔHvap scales approximately with Tb. Antoine equation correlates vapour pressure vs temperature, not directly ΔHvap; Kopp’s rule estimates heat capacity from atomic contributions; Kistyakowsky is not the relevant common name here. Thus, the correct named relation is Trouton’s rule.

Step-by-Step Solution:Recall ΔSvap ≈ constant at Tb.Therefore, ΔHvap ≈ Tb * constant.Select Trouton’s rule.

Verification / Alternative check:Comparing liquids like benzene, toluene, hexane shows ΔHvap/Tb values clustering around Trouton’s constant, except for hydrogen-bonded liquids like water.

Why Other Options Are Wrong:Antoine is Pvap–T; Kopp is for heat capacity; “Clapeyron integral” is a general thermodynamic relation, not the empirical rule asked.

Common Pitfalls:Applying Trouton’s rule to strongly associating liquids leads to significant errors.

Final Answer:Trouton's rule