Q: A sample of 2.58 kg of water is to be vaporized at its normal boiling point. If the enthalpy of vaporization $$\Delta H_{\text{vap}}$$ for water is $$40.7\ \mathrm{kJ\ $$mol^{-1}$$}$$, how much heat (in kJ) is required? (Molar mass of water = $$18.02\ \mathrm{g\ $$mol^{-1}$$})$$

$$5.83 \times 10^3$\ \mathrm{kJ}$$

Question 1

Which of the following substances would you expect to have the highest boiling point, and why?

Accepted Answer

HF, because it forms strong hydrogen bonds.

Question 2

Which intermolecular force is present in all molecules, regardless of their polarity?

Accepted Answer

London Dispersion Forces

Question 3

A sample of 2.58 kg of water is to be vaporized at its normal boiling point. If the enthalpy of vaporization $$\Delta H_{	ext{vap}}$$ for water is $$40.7\ \mathrm{kJ\ $$mol^{-1}$$}$$, how much heat (in kJ) is required? (Molar mass of water = $$18.02\ \mathrm{g\ $$mol^{-1}$$})$$

Accepted Answer

$$5.83 	imes 10^3$\ \mathrm{kJ}$$

Question 4

Which of the following best explains why acetone is more volatile than water at room temperature?

Accepted Answer

Acetone has weaker intermolecular forces than water.

Question 5

Which of the following statements about vaporization is correct?

Accepted Answer

Vaporization is an endothermic process because energy is required to overcome intermolecular forces.

Question 6

A 100 mL sample of water is placed in a 250 mL beaker with a 7 cm diameter at 55°C. Compared to a 100 mL sample in a 100 mL beaker with a 5 cm diameter at 25°C, which will have the highest rate of vaporization and why?

Accepted Answer

The 100 mL sample at 55°C in the 250 mL beaker, because both higher temperature and larger surface area increase the rate of vaporization.

Question 7

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

Accepted Answer

Stronger IMF leads to lower vapor pressure.

Question 8

Which of the following compounds would have the highest vapor pressure at room temperature?

Accepted Answer

A nonpolar compound with low molar mass

Question 9

Which of the following is NOT a requirement for hydrogen bonding to occur between molecules?

Accepted Answer

The molecule must have a high molar mass.

Question 10

Which halogen has the highest boiling point, and what is the main reason?

Accepted Answer

I$$_2$$, because it has the highest molar mass and thus the strongest London dispersion forces.

Question 11

Which of the following best describes the process of dynamic equilibrium in a closed container of liquid and its vapor?

Accepted Answer

The rate of evaporation equals the rate of condensation.

Question 12

Which of the following statements about boiling point is correct?

Accepted Answer

The boiling point is the temperature at which the vapor pressure of a liquid equals the external pressure.

Question 13

Which of the following best explains why ionic compounds like NaCl dissolve in water?

Accepted Answer

Ion-dipole forces between the ions and polar water molecules are strong enough to overcome the ionic lattice.

Question 14

Which of the following changes will NOT increase the vapor pressure of a liquid in a closed container?

Accepted Answer

Increasing the surface area of the liquid

Question 15

A liquid has a normal boiling point of 78°C and an enthalpy of vaporization $$\Delta H_{	ext{vap}} of$$ $$38.7\ \mathrm{kJ\ $$mol^{-1}$$}. $$Using the Clausius-Clapeyron equation, what is the vapor pressure (in mmHg) at 29°C if the vapor pressure at 78°C is 760 mmHg? (Use $$R = 8.314\ \mathrm{J\ $$mol^{-1}$$\ K$$^{-1}$$})$$

Accepted Answer

$$95\ \mathrm{mmHg}$$

Question 16

Which of the following best describes the effect of molecular shape on London dispersion forces?

Accepted Answer

Molecules with larger surface area have stronger London dispersion forces.

Question 17

Which of the following is true about the enthalpy of vaporization ($$\Delta H_{	ext{vap}}) $$and condensation?

Accepted Answer

$$\Delta H_{	ext{vap}} is $$positive, while $$\Delta H_{	ext{cond}} is $$negative.

Question 18

Which of the following best explains why polar molecules generally have higher boiling points than nonpolar molecules of similar molar mass?

Accepted Answer

Polar molecules experience both dipole-dipole and London dispersion forces.

Question 19

Which of the following is the strongest type of intermolecular force?

Accepted Answer

Ion-dipole force

Question 20

Which of the following best describes the effect of increasing temperature on the rate of vaporization?

Accepted Answer

The rate of vaporization increases because more molecules have enough energy to overcome intermolecular forces.

Liquids, Solids, and Intermolecular Forces: Properties, Vaporization, and Boiling Point

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