Chapter 7, Problem 7.106EP

(a)

Interpretation Introduction

Interpretation:

Between $\text{He}$ and $\text{Ne}$ which one has the higher boiling point has to be determined.

Concept Introduction:

Boiling point:

Boiling is a form of evaporation where the conversion from the liquid state to vapor state occurs within the body of the liquid through bubble formation.

A normal boiling point is the temperature at which the liquid boils under a pressure of $\text{760}\text{mm}\text{Hg}$.  It is the temperature at which the vapor pressure of the liquid becomes equal to the external pressure exerted on the liquid.

London force:

London force is a type of weak intermolecular force that has an effect on boiling point.  This weak temporary force occurs between two atoms or molecules (polar or non-polar)

The cause of London force is the temporary uneven distribution of electrons causing induced polarity.  The strength of the London force depends on how easily a molecule can be distorted or polarized by the polarity present in another molecule.  For the large molecules the outermost electrons are far from nucleus and as the result the attractive forces of nucleus acting on them are very weak and hence the outermost electrons can be easily polarized.  Hence the induced polar molecule and the polar molecule will attract each other more.

Thus the molecules having higher mass have higher boiling point.

(b)

Interpretation Introduction

Interpretation:

Between ${\text{H}}_2$ and $\text{HCl}$ which one has the higher boiling point has to be determined.

Concept Introduction:

Boiling point:

Boiling is a form of evaporation where the conversion from the liquid state to vapor state occurs within the body of the liquid through bubble formation.

A normal boiling point is the temperature at which the liquid boils under a pressure of $\text{760}\text{mm}\text{Hg}$.  It is the temperature at which the vapor pressure of the liquid becomes equal to the external pressure exerted on the liquid.

Dipole-dipole interaction:

Dipole- dipole interactions are the strong intermolecular interaction that causes between two polar molecules.

In polar molecules there will be a force of attraction between the positive end and the negative end.  Hence the molecules having higher electronegativity difference i.e. having more polarity will have higher dipole-dipole intermolecular attraction acting between them and as a result the boiling point will increase.

(c)

Interpretation Introduction

Interpretation:

Between $\text{ClF}$ and $\text{HF}$ which one has the higher boiling point has to be determined.

Concept Introduction:

Hydrogen bonding:

Hydrogen bonding is an intermolecular force.  This is an extra strong dipole-dipole interaction between a hydrogen atom covalently bonded to a small electronegative atom mainly $\text{F}\text{,}\text{O}\text{,}\text{N}$ and a lone pair of another nearby electronegative atom like $\text{F}\text{,}\text{O}\text{,}\text{N}$.

The vapor pressure of liquids having significant hydrogen bonding are much lower than those liquids having no hydrogen bonding.  Because of presence of extensive hydrogen bonding the liquid molecules face difficulty to escape from the condensed state and additional energy is required to break the hydrogen bonds and go to the vapor state and as a result the liquids having extensive hydrogen bonding have higher boiling points.

Dipole-dipole interaction:

Dipole- dipole interactions are the strong intermolecular interaction that causes between two polar molecules.

In polar molecules there will be a force of attraction between the positive end and the negative end.  Hence the molecules having higher electronegativity difference i.e. having more polarity will have higher dipole-dipole intermolecular attraction acting between them and as a result the boiling point will increase.

(d)

Interpretation Introduction

Interpretation:

Between $\text{CO}$ and ${\text{N}}_2$ which one has the higher boiling point has to be determined.

Concept Introduction:

Dipole-dipole interaction:

Dipole- dipole interactions are the strong intermolecular interaction that causes between two polar molecules.

In polar molecules there will be a force of attraction between the positive end and the negative end. Hence the molecules having higher electronegativity difference i.e. having more polarity will have higher dipole-dipole intermolecular attraction acting between them and as a result the boiling point will increase.