Question 1

Which of the following statements best explains why ice floats on water, but solid benzene sinks in liquid benzene?

Accepted Answer

Ice is less dense than liquid water due to the open hydrogen-bonded structure of ice.

Question 2

Which intermolecular force is primarily responsible for the high boiling point of water compared to other group 16 hydrides?

Accepted Answer

Hydrogen bonding

Question 3

A sample of diethyl ether has a vapor pressure of 401 mmHg at 18°C (291 K). Given $$\Delta H_{vap} = 26.0\ \mathrm{kJ/mol}$$, what is the vapor pressure at 32°C (305 K)? Use $$R = 8.314\ \mathrm{J/(mol\cdot K)}$$ and the Clausius-Clapeyron equation.

Accepted Answer

$$P_2 = 760$$\ \mathrm{mmHg}$$

Question 4

Which of the following best describes the difference between intramolecular and intermolecular forces?

Accepted Answer

Intramolecular forces are bonds within a molecule, while intermolecular forces are attractions between molecules.

Question 5

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

Accepted Answer

Glycerol, due to extensive hydrogen bonding.

Question 6

Which of the following best explains why the boiling point of water decreases at higher altitudes?

Accepted Answer

The external pressure is lower, so the vapor pressure required for boiling is reached at a lower temperature.

Question 7

Which of the following is NOT a requirement for hydrogen bonding?

Accepted Answer

Hydrogen must be bonded to a carbon atom.

Question 8

Which of the following phase changes is exothermic?

Accepted Answer

Condensation

Question 9

A liquid in a narrow tube rises up the walls of the tube. Which property and force are primarily responsible for this behavior?

Accepted Answer

Capillary action due to adhesion between the liquid and the tube.

Question 10

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

Accepted Answer

The rate of evaporation equals the rate of condensation.

Question 11

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

Accepted Answer

Argon (Ar)

Question 12

Which of the following best explains why the heat of sublimation is equal to the sum of the heat of fusion and the heat of vaporization?

Accepted Answer

Sublimation is a direct transition from solid to gas, which is equivalent to melting followed by vaporization.

Question 13

Which of the following best describes the critical temperature of a substance?

Accepted Answer

The highest temperature at which a substance can exist as a liquid.

Question 14

Which of the following is the strongest type of intermolecular force present in a solution of NaCl dissolved in water?

Accepted Answer

Ion-dipole interactions

Question 15

Which of the following best explains why water has a high specific heat compared to other small molecules?

Accepted Answer

Extensive hydrogen bonding requires more energy to increase the temperature.

Question 16

Which of the following equations is the Clausius-Clapeyron equation used to relate vapor pressure and temperature?

Accepted Answer

$$\ln P = \left( -\frac{\Delta H_{vap}}{R} \right) \left( \frac{1}{T} \right) + C$$

Question 17

Which of the following best describes the effect of increasing molecular size on dispersion forces?

Accepted Answer

Dispersion forces increase with increasing molecular size.

Question 18

Which of the following phase changes is correctly paired with its enthalpy term?

Accepted Answer

Melting: $$\Delta H_{fus}$$

Question 19

Which of the following best explains why mercury forms a convex meniscus in a glass tube, while water forms a concave meniscus?

Accepted Answer

Mercury has stronger cohesion than adhesion to glass, while water has stronger adhesion to glass than cohesion.

Intermolecular Forces, Properties of Solids and Liquids, and Phase Changes

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