Question

In each of the following groups of substances, pick the one that has the given property. Justify your answer.

a. highest boiling point: HBr, Kr, CI₂

b. highest freezing point: H₂O, NaCI, or HF

c. lowest vapor pressure at 25⁰C: CI₂, Br, or I₂

d. lowest freezing point: N₂, CI, or CO₂

e. lowest boiling point: CH₄, CH₃, CH₃, or CH₃CH₂CH₃

f. highest boiling point: HF, HCI, or HBr

g. lowest vapor pressure at 25^OC : CH₃CH₂CH₃ or CH₃CH₂CH₂OH

Short answer

a)Highest boiling point: HBr has the highest boiling point because it has dipole-dipole interaction, which is known as one of the strongest intermolecular forces.

b)Highest freezing point is NaCl.

NaCl has the highest freezing point because it is an ionic compound. The ionic bond in NaCl has a stronger attractive force than any other intermolecular force.

c) Lowest vapor pressure at 25⁰C is I₂ .

I₂ has lower vapor pressure because it exists in a solid state and has stronger intermolecular forces than other halogen intermolecular forces.

d) Lowest freezing point: N₂ has the lowest freezing point because it has the weakest interactions as it is the smallest molecule and exerts only London dispersion forces.

e) Lowest boiling point: CH₄ has the lowest boiling point because it has the smallest molecule and will have the weakest London dispersion forces.

f)Highest boiling point: HF has the highest boiling point because it has the strongest dipole-dipole forces due to hydrogen bonding.

g) Lowest vapor pressure at 25^OC:

CH₃CH₂CH₂OH has the lowest vapor pressure at 25^OC . It has the strongest intermolecular forces because of the strongest dipole-dipole forces due to hydrogen bonding.

Step-by-step solution

Intermolecular force

Intramolecular forces are well-known forces that work between the molecules as they hold atoms of the molecule together within a molecule.Intermolecular forces exist between molecules of any compound, such as in water molecules.

Step-2 Types of intermolecular forces

There are mainly four types of intermolecular forces present.

1. London depression force

2. Dipole-Dipole force

3. Hydrogen bonding.

4. Ion-Dipole force

Explanation

a)Highest boiling point: HBr has the highest boiling point because it has dipole-dipole interaction, which is known as one of the strongest intermolecular forces.

b)Highest freezing point is NaCl.

NaCl has the highest freezing point because it is an ionic compound. The ionic bond in NaCl has a stronger attractive force in comparison to any other intermolecular force.

c) Lowest vapor pressure at 25⁰C is I₂ .

I₂ has lower vapor pressure because it exists in a solid state and has stronger intermolecular forces than other halogen intermolecular forces.

d) Lowest freezing point: N₂ has the lowest freezing point because it has the weakest interactions because it is the smallest molecule and exerts only London dispersion forces.

e) Lowest boiling point: CH₄ has the lowest boiling point because it has the smallest molecule of all and will have the weakest London dispersion forces.

f)Highest boiling point: HF has the highest boiling point because it has the strongest dipole-dipole forces due to hydrogen bonding.

g) Lowest vapor pressure at 25^oC :

CH₃CH₂CH₂OH has the lowest vapor pressure at 25^oC . It has the strongest intermolecular forces because it has the strongest dipole-dipole forces due to hydrogen bonding.