Question 1

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

Accepted Answer

Ammonia (NH$$_3$$), because it can form hydrogen bonds.

Question 2

A sample of water is heated from 25$$^\circC to 100$^\circC $$and then boiled completely to steam at 100$$^\circC. $$Which equation(s) would you use to calculate the total energy required?

Accepted Answer

First $$q = m c \Delta T$$ for heating, then $$q = n \Delta H_{vap}$$ for boiling.

Question 3

Which of the following best explains why ice melts under pressure, but most solids do not?

Accepted Answer

The solid-liquid line in water's phase diagram has a negative slope, indicating that increasing pressure favors the liquid phase.

Question 4

Which of the following statements about intermolecular forces is correct?

Accepted Answer

Hydrogen bonding occurs in molecules where hydrogen is bonded to F, O, or N.

Question 5

A crystalline solid has a coordination number of 12 and an 'abcabc' stacking pattern. What type of unit cell does it have?

Accepted Answer

Face-centered cubic

Question 6

Which of the following best describes the difference between adhesion and cohesion in liquids?

Accepted Answer

Cohesion is the attraction between like molecules; adhesion is the attraction between unlike molecules.

Question 7

Which compound would you expect to have the highest lattice energy?

Accepted Answer

MgO

Question 8

A metal crystallizes in a body-centered cubic (bcc) structure. If the edge length of the unit cell is $$a$$, what is the relationship between the atomic radius $$r$$ and $$a$$?

Accepted Answer

$$a = \dfrac{4r}{\sqrt{3}}$$

Question 9

Which of the following best explains why LiF has a higher lattice energy than CsI?

Accepted Answer

Li$$^+$$ and F$$^-$$ are smaller ions, so their charges are closer together, increasing lattice energy.

Question 10

Which of the following statements about vapor pressure is correct?

Accepted Answer

A liquid boils when its vapor pressure equals atmospheric pressure.

Question 11

A sample of an unknown solid is found to have a random arrangement of particles and does not exhibit long-range order. This solid is best classified as:

Accepted Answer

Amorphous

Question 12

Which of the following best describes the role of polarizability in London dispersion forces?

Accepted Answer

Larger atoms are more polarizable, resulting in stronger London dispersion forces.

Question 13

Which of the following is a network atomic solid?

Accepted Answer

Diamond (C)

Question 14

A salt is found to be very hard, has a high melting point, and is only slightly soluble in water. What can you infer about its lattice energy?

Accepted Answer

It has a high lattice energy.

Question 15

Which of the following best describes the process of capillary action?

Accepted Answer

It is caused by the balance between adhesion and surface tension.

Question 16

Which equation would you use to calculate the distance between planes in a crystal using X-ray diffraction data?

Accepted Answer

$$n\lambda = 2d\sin	heta$$

Question 17

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

Accepted Answer

It is the temperature and pressure where all three phases (solid, liquid, gas) coexist.

Question 18

Which of the following best explains why NaCl has a higher melting point than H$$_2O$$?

Accepted Answer

NaCl is held together by strong ionic bonds, while H$$_2O is $$held together by weaker intermolecular forces.

Question 19

A sample of a metallic solid is analyzed and found to have a 'sea of electrons' model. Which property is most directly explained by this model?

Accepted Answer

Electrical conductivity

Question 20

Which of the following is the correct formula for calculating the density of a unit cell?

Accepted Answer

$$	ext{Density} = \dfrac{	ext{mass of atoms in unit cell}}{	ext{volume of unit cell}}$$

Exam 2 Study Guide: Intermolecular Forces, Solids, and Lattice Energy

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