Question

The liquid that deviates from the Trouton’s rule is:
(A) Hydrochloric acid
(B) Sulphuric acid
(C) Phosphoric acid
(D) Acetic acid

Answer 1

The law which states that the entropy of vaporization value is almost same (about ${\text{85 - 88Jmo}}{{\text{l}}^{{\text{ - 1}}}}{{\text{K}}^{{\text{ - 1}}}}$ ) for various different type of liquids at their boiling points is known as Trouton’s law. Hydrogen bonding plays a vital role in this law.

Complete step by step answer:
Trouton’s law: This law states that the entropy of vaporization value is almost same, which is about ${\text{85 - 88Jmo}}{{\text{l}}^{{\text{ - 1}}}}{{\text{K}}^{{\text{ - 1}}}}$ for various liquids at their boiling point temperatures.
The ratio of enthalpy of vaporization and boiling temperature is known as entropy of vaporization. It can also be said as Trouton’s ratio.
The formula related to entropy of vaporization is as follows:
$\dfrac{{{{\text{L}}_{{\text{vap}}}}}}{{{{\text{T}}_{{\text{boil}}}}}} = {\text{85 - 88Jmo}}{{\text{l}}^{{\text{ - 1}}}}{{\text{K}}^{{\text{ - 1}}}}$
As we all know that in chemistry exceptions are everywhere so some exceptions are also found in this Trouton’s law. The entropies of vaporization for water, formic acid, ethanol , hydrogen fluoride, etc. are far away from the predicted values so these chemical compounds do not follow Trouton’s law or we can say deviated from Trouton's law.
The chemical compounds which do not obey Trouton’s law have a special interaction between their molecules. This special interaction is hydrogen bonding. So we can say that chemical compounds having hydrogen bonding does not obey Trouton’s law.
So from the above discussion we can conclude that the liquid that deviates from Trouton's rule is acetic acid as it shows hydrogen bonding with the similar molecules of acetic acid.
Hence option (D) is the correct answer.

Note:
As we all know that hydrogen bonding has an impact or we can say the cause of deviation from the Trouton’s law because due to hydrogen bonding the boiling point of the chemical compound changes and hence entropy of vaporization changes.