How bonding, structure, and interparticle interactions are related to the physical properties of pure substances

Question 1

Based only on their intermolecular forces, which between O2, CH3OH, and CO2 would have the highest boiling point?

Answer 1

CH3OH

Methanol (CH3OH) has a hydrogen bonding, while CO2 and O2 are both nonpolar molecules, tha could only experiences London dispersion forces. Since hydrogen bonding is stronger than London forces, C2H5OH as the highest boiling point.

Question 2

Based only on their intermolecular forces, which between CH2Cl2, C2H6, and C2H5OH would have the highest melting point?

Answer 2

C2H5OH

C2H5OH has a hydrogen bonding, while CH2Cl2 has a dipole-dipole interaction, and C2H6 is nonpolar molecules, tha could only experiences London dispersion forces. Since hydrogen bonding is stronger than both dipole-dipole and London forces, C2H5OH as the highest melting point.

Question 3

What will happen to the rate of vaporization if the temperature is decreased?

Answer 3

The rate of vaporization will also decrease

The average kinetic energy of the particles falls as the temperature drops. As a result, fewer particles will possess the energy required to overcome the interactions between molecules and evaporate.

Question 4

Arrange the following compounds in order of increasing melting point.
HCl, HF, HBr, HI

Answer 4

HI < HBr < HCl < HF

All compounds exhibits dipole-dipole and London forces. And all compounds are each attached to H- only and the other is a halogen, to compare the relative melting points, we can rank them according to their electronegativies. Halogen with higher electronegativiy would have a higher melting point.

Question 5

If methanol has a heat of vaporization 35.21 kJ/mol and a normal boiling point of 64.6°C. Determine the vapor pressure (in atm) of methanol at 25.0 °C.

Answer 5

0.189 atm

Use the Clausius–Clapeyron Equation to calculate.