Question 1

Which of the following best explains why water ($$\mathrm{H_2O}) is a $$liquid at room temperature while methane ($$\mathrm{CH_4$}) is a $$gas, despite their similar molar masses?

Accepted Answer

Water molecules form strong hydrogen bonds, while methane molecules only experience London dispersion forces.

Question 2

Which phase change is represented by $$\Delta H_{\mathrm{fusion}}$$ and what does it physically mean?

Accepted Answer

$$\Delta H_{\mathrm{fusion}} is $$the enthalpy change for melting, representing the energy required to convert a solid to a liquid.

Question 3

A molecule of ammonia ($$\mathrm{NH_3$}) $$can form which type of intermolecular force with another $$\mathrm{NH_3$}$$ molecule?

Accepted Answer

Hydrogen bonding

Question 4

Which of the following molecules would have the strongest London dispersion forces?

Accepted Answer

$$\mathrm{C_8H_{18}} ($$octane)

Question 5

Which of the following statements about phase changes is correct?

Accepted Answer

Sublimation is the direct transition from solid to gas, and its enthalpy change is $$\Delta H_{\mathrm{subl}}.$$

Question 6

Which of the following best describes the geometry of a molecule with four electron groups and two lone pairs on the central atom?

Accepted Answer

Bent

Question 7

A student claims that $$\mathrm{CH_3F} is $$nonpolar because it contains mostly C and H atoms. What is wrong with this reasoning?

Accepted Answer

$$\mathrm{CH_3F}$$ contains fluorine, which is highly electronegative, making the molecule polar.

Question 8

Which of the following is true about the compressibility and density of gases compared to solids and liquids?

Accepted Answer

Gases have high compressibility and low density compared to solids and liquids.

Question 9

Which of the following molecules can form hydrogen bonds with water?

Accepted Answer

$$\mathrm{NH_3$}$$

Question 10

Which of the following best explains why larger, more spread-out molecules have stronger London dispersion forces?

Accepted Answer

They have more electrons and a larger surface area, increasing polarizability.

Question 11

A solution of sodium chloride ($$\mathrm{NaCl}) in $$water is an example of which type of intermolecular force?

Accepted Answer

Ion-dipole force

Question 12

Which of the following statements about molecular polarity is correct?

Accepted Answer

A molecule with only C and H atoms is generally nonpolar.

Question 13

Which of the following phase changes is exothermic?

Accepted Answer

Freezing

Question 14

If a molecule has polar bonds but a symmetrical geometry, what is the overall molecular polarity?

Accepted Answer

The molecule is nonpolar because the bond dipoles cancel out.

Question 15

Which of the following best describes the relationship between temperature and the kinetic energy of particles in a substance?

Accepted Answer

Higher temperature means higher average kinetic energy of the particles.

Question 16

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

Accepted Answer

Ion-dipole force

Question 17

A molecule with a trigonal planar geometry and no lone pairs on the central atom is most likely to have which bond angle?

Accepted Answer

$$120^\circ$$

Question 18

Which of the following best describes the process of deposition?

Accepted Answer

A gas changes directly to a solid, releasing energy.

Question 19

Which of the following molecules would you expect to have only London dispersion forces as its strongest intermolecular force?

Accepted Answer

$$\mathrm{C_6H_{14}} ($$hexane)

Question 20

Which of the following best explains why the boiling point of $$\mathrm{H_2O} is $$much higher than that of $$\mathrm{CH_4$}$$?

Accepted Answer

$$\mathrm{H_2O}$$ forms hydrogen bonds, which require more energy to break than the London dispersion forces in $$\mathrm{CH_4$}.$$

CH 10

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