Question 1

Which of the following best explains why water has a much higher boiling point than methane ($\mathrm{CH_4}$), even though both are small molecules?

Accepted Answer

Water molecules form strong hydrogen bonds with each other, requiring more energy to separate them.

Question 2

A sample of liquid is observed to form a meniscus that curves upward at the edges when placed in a glass tube. Which statement best explains this observation?

Accepted Answer

The adhesive forces between the liquid and glass are stronger than the cohesive forces within the liquid.

Question 3

Which of the following statements about vapor pressure is correct?

Accepted Answer

Vapor pressure increases as temperature increases because more molecules have enough energy to escape the liquid phase.

Question 4

Which equation is used to relate the vapor pressure of a liquid at two different temperatures?

Accepted Answer

$\ln \left( \frac{P_2}{P_1} \right) = -\frac{\Delta H_{vap}}{R} \left( \frac{1}{T_2} - \frac{1}{T_1} \right)$

Question 5

A liquid has a high surface tension. Which of the following is most likely true about its intermolecular forces?

Accepted Answer

The liquid has strong intermolecular forces, such as hydrogen bonding or dipole-dipole interactions.

Question 6

Which of the following best describes the process of sublimation?

Accepted Answer

A solid changes directly into a gas without passing through the liquid phase.

Question 7

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

Accepted Answer

Glycerol ($\mathrm{C_3H_8O_3}$), due to its extensive hydrogen bonding.

Question 8

A sample of water is heated from $20^\circ \mathrm{C}$ to $100^\circ \mathrm{C}$ at 1 atm. Which segment of the heating curve corresponds to the phase change from liquid to gas?

Accepted Answer

The flat segment at $100^\circ \mathrm{C}$, where temperature remains constant as water boils.

Question 9

Which of the following best explains why ionic solids generally have higher melting points than molecular solids?

Accepted Answer

Ionic solids are held together by strong electrostatic forces between oppositely charged ions.

Question 10

Which of the following statements about phase diagrams is correct?

Accepted Answer

The triple point is the unique set of conditions where all three phases (solid, liquid, gas) coexist in equilibrium.

Question 11

A chemist wants to increase the rate at which a solid dissolves in a liquid. Which of the following actions would be most effective?

Accepted Answer

Increasing the temperature of the solvent.

Question 12

Which of the following best describes the concept of polarizability?

Accepted Answer

The ease with which the electron cloud of a molecule can be distorted, affecting the strength of London dispersion forces.

Question 13

Which of the following is the correct formula for calculating the energy required to vaporize a given mass of a liquid?

Accepted Answer

$q = n \Delta H_{vap}$

Question 14

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

Accepted Answer

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

Question 15

Which of the following statements about the relationship between viscosity and intermolecular forces is correct?

Accepted Answer

Liquids with stronger intermolecular forces generally have higher viscosity.

Question 16

A sample of ethanol ($\mathrm{C_2H_5OH}$) and a sample of hexane ($\mathrm{C_6H_{14}}$) are placed in open containers at the same temperature. Which will evaporate faster and why?

Accepted Answer

Hexane will evaporate faster because it has weaker intermolecular forces than ethanol.

Question 17

Which of the following is true about the critical point on a phase diagram?

Accepted Answer

Above the critical temperature and pressure, the liquid and gas phases become indistinguishable.

Question 18

Which of the following best describes the relationship between boiling point and intermolecular forces?

Accepted Answer

A higher boiling point generally indicates stronger intermolecular forces.

Question 19

Which of the following is a quantitative measure of the process of vaporization?

Accepted Answer

$\Delta H_{vap}$, the enthalpy of vaporization.

Question 20

Which of the following best explains why iodine ($\mathrm{I_2}$) sublimes at room temperature?

Accepted Answer

Iodine has weak London dispersion forces relative to its molecular mass, allowing it to transition directly from solid to gas.

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