Chapter 3, Problem 3B.9E

(a)

Interpretation Introduction

Interpretation:

The entropy of vaporization of octane has to be estimated.

Concept Information:

Entropy of vaporization: The entropy of vaporization at the boiling temperature of a liquid is related to its enthalpy of vaporization at that temperature.

${\text{Δ}}_{vap}\text{S}\text{=}\frac{{\text{Δ}}_{vap}\text{H}\left({\text{T}}_b\right)}{{\text{T}}_b}$

Where,

${\text{Δ}}_{vap}\text{S}$ is change in entropy of vaporization,

${\text{Δ}}_{vap}\text{H}$ is change in enthalpy of vaporization,

${\text{T}}_b$ is the boiling temperature.

(b)

Interpretation Introduction

Interpretation:

The enthalpy of vaporization of octane has to be estimated.

Concept Information:

Trouton’s rule: In the vaporization of liquid, the condensed (or less disordered) phase of liquid vaporizes into the gaseous phase, where the dispersed gas occupies approximately same volume whatever its identity.

Then, considering value of the change in entropy of such liquids is constant as $\text{85}{\text{JK}}^{\text{-1}}{\text{mol}}^{\text{-1}}$

Trouton’s rule exception: For exceptional liquids having special kind of interactions like hydrogen bonding and metallic bonding result in the liquid being less disordered than a random jumble of molecules. There exists high value of entropy change.

Entropy of vaporization: The entropy of vaporization at the boiling temperature of a liquid is related to its enthalpy of vaporization at that temperature.

${\text{Δ}}_{vap}\text{S}\text{=}\frac{{\text{Δ}}_{vap}\text{H}\left({\text{T}}_b\right)}{{\text{T}}_b}$

Where,

${\text{Δ}}_{vap}\text{S}$ is change in entropy of vaporization,

${\text{Δ}}_{vap}\text{H}$ is change in enthalpy of vaporization,

${\text{T}}_b$ is the boiling temperature.