Trouton’s ratio and Kistyakowsky correlation: for which liquids is the Kistyakowsky equation used to estimate λb/Tb?

Introduction / Context:
Trouton’s rule states that many liquids have λ_b/T_b ≈ 21 cal/mol·K at their normal boiling points. Deviations occur, especially for associating or polar liquids. The Kistyakowsky equation refines the estimate for certain classes of liquids.

Given Data / Assumptions:

• Trouton’s ratio λ_b/T_b around 21 holds best for simple, non-associating liquids.
• Kistyakowsky correlation targets such systems.

Concept / Approach:
Non-polar, relatively symmetric molecules tend to follow Trouton’s rule closely, and the Kistyakowsky equation provides a semi-empirical correction for improved accuracy. Polar and hydrogen-bonded liquids (e.g., water, alcohols) deviate significantly and are not well described by this simple relation.

Step-by-Step Solution:
Identify the class of liquids with near-constant λ_b/T_b values: non-polar.Note that Kistyakowsky's correlation is intended for those relatively ideal, non-associating liquids.Therefore, select “non-polar.”

Verification / Alternative check:
Data tables show hydrocarbons and noble-element compounds conform better to Trouton/Kistyakowsky than strongly polar or hydrogen-bonding liquids.

Why Other Options Are Wrong:
Polar and associating liquids diverge from the ~21 value; “both” or “neither” contradict the intended scope of the equation.

Common Pitfalls:
Overgeneralizing Trouton’s rule to all liquids, including hydrogen-bonded ones.

Final Answer:
non-polar