Question 1

Which of the following statements best explains why water (H$$_2O) is a $$liquid at room temperature while methane (CH$$_4) is a $$gas, despite their similar molar masses?

Accepted Answer

Water molecules form hydrogen bonds, which are much stronger than the London dispersion forces present in methane.

Question 2

Which type of intermolecular force is primarily responsible for the high boiling point of hydrogen fluoride (HF) compared to hydrogen chloride (HCl)?

Accepted Answer

Hydrogen bonding

Question 3

A sample of NaCl is dissolved in water. Which type of intermolecular force is most significant between the Na$$^+$$ ions and the water molecules?

Accepted Answer

Ion-dipole forces

Question 4

Which of the following molecules would you expect to have the highest viscosity at room temperature?

Accepted Answer

Glycerol (C$$_3H$_5(OH$$)$$_3)$$

Question 5

Which of the following best describes the process of vaporization?

Accepted Answer

It requires energy to overcome intermolecular forces and convert a liquid to a gas.

Question 6

Which of the following phase changes is exothermic?

Accepted Answer

Condensation

Question 7

A phase diagram for water shows a negative slope for the solid-liquid boundary. What does this indicate about the relative densities of ice and liquid water?

Accepted Answer

Ice is less dense than liquid water.

Question 8

Which of the following molecules would have only London dispersion forces as its primary intermolecular force?

Accepted Answer

Argon (Ar)

Question 9

Which of the following factors increases the strength of London dispersion forces in a molecule?

Accepted Answer

Increasing molecular mass

Question 10

Which of the following best explains why surface tension in water is higher than in most other liquids?

Accepted Answer

Water molecules form extensive hydrogen bonds at the surface.

Question 11

A pressure cooker operates at 1.50 atm. Given that the enthalpy of vaporization ($$\Delta H_{vap}) of $$water is 40.7 kJ/mol, estimate the boiling point of water in the pressure cooker using the Clausius-Clapeyron equation. (Assume normal boiling point is 100$$^\circC at 1 $$atm.)

Accepted Answer

$$\approx 112^\circC$$

Question 12

Which of the following statements about phase diagrams is correct?

Accepted Answer

The triple point is where solid, liquid, and gas phases coexist in equilibrium.

Question 13

Which of the following molecules would have the highest boiling point?

Accepted Answer

Water (H$$_2O)$$

Question 14

Which of the following best describes the relationship between intermolecular forces and vapor pressure?

Accepted Answer

Stronger intermolecular forces result in lower vapor pressure.

Question 15

Which of the following is a real-life consequence of hydrogen bonding in water?

Accepted Answer

Ice floats on liquid water, allowing aquatic life to survive in winter.

Question 16

Which of the following best explains why carbon dioxide (CO$$_2) is a $$nonpolar molecule despite having polar bonds?

Accepted Answer

The bond dipoles cancel each other due to the linear geometry.

Question 17

Which of the following would increase the boiling point of a liquid?

Accepted Answer

Increasing the strength of intermolecular forces

Question 18

Which of the following best describes the critical point on a phase diagram?

Accepted Answer

The temperature and pressure above which a gas cannot be liquefied

Question 19

Which of the following is NOT a property primarily determined by intermolecular forces?

Accepted Answer

Molecular formula

Question 20

Which of the following best explains why 2,2-dimethylpropane has a lower boiling point than n-pentane, even though they have the same molecular formula (C$$_5H$_{12}$$)?

Accepted Answer

2,2-dimethylpropane is more compact, resulting in weaker London dispersion forces.

Liquids and Phase Changes: Intermolecular Forces and Properties of Liquids

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