Question

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

a. highest boiling point: CCI₄, CF₄, CBr₄

b. lowest freezing point: LiF, F₂, HCI

c. lowest vapor pressure at 25^oC : CH₃OCH₃, CH₃CH₂OH, CH₃CH₂CH₃

d. greatest viscosity: H₂S, HF, or H₂O₂

e. greatest heat of vaporization: H₂CO, CH₃CH₃, CH₄

f. smallest enthalpy of fusion: I₂, CsBr, or CaO.

Short answer

a)Highest boiling point: CBr₄ has the highest boiling point because stronger dispersion forces would occur between the molecules of CBr₄ as it has higher molecular weight.

b) Lowest freezing point: F₂ has the lowest freezing point because it has only London dispersion forces, also known as the weakest intermolecular force.

c) Lowest vapor pressure is there for CH₃CH₂OH has the lowest vapor pressure at 25^oC. Because it has the strongest dipole-dipole forces due to hydrogen bonding, this is also known as the strongest intermolecular force.

d)Greatest viscosity: H₂O₂ has the greatest viscosity because it has more hydrogen bonding than HF as it can form hydrogen bonds at both ends of the molecule.

e)Greatest heat of vaporization: H₂CO has the greatest heat of vaporization because it has the dipole-dipole interactions, which are also known as one of the strongest intermolecular forces.

f)Smallest enthalpy of fusion: I₂ has only London dispersion forces, whereas CsBr and CaO have much stronger ionic forces. I₂ has the weakest intermolecular forces, so it has the smallest enthalpy of fusion.

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.

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: CBr₄ has the highest boiling point because stronger dispersion forces would occur between the molecules of CBr₄ as it has higher molecular weight.

b) Lowest freezing point: F₂ has the lowest freezing point because it has only London dispersion forces, also known as the weakest intermolecular force.

c) Lowest vapor pressure is there for CH₃CH₂OH has the lowest vapor pressure at 25^oC. Because it has the strongest dipole-dipole forces due to hydrogen bonding, this is also known as the strongest intermolecular force.

d)Greatest viscosity: H₂O₂ has the greatest viscosity because it has more hydrogen bonding than HF as it can form hydrogen bonds at both ends of the molecule.

e)Greatest heat of vaporization: H₂CO has the greatest heat of vaporization because it has the dipole-dipole interactions, which are also known as one of the strongest intermolecular forces.

f)Smallest enthalpy of fusion: I₂ has only London dispersion forces, whereas CsBr and CaO have much stronger ionic forces. I₂ has the weakest intermolecular forces, so it has the smallest enthalpy of fusion.