Chapter 12 Homework

Question 1

A silver crystal has a face-centered cubic unit cell. This is the closest silver atoms can be packed. What fraction of the unit cell in a silver crystal is empty space? The radius of a silver atom is 144 pm (though you don’t technically need this number to answer the question).

Answer 1

26%

Question 2

Which of the following does not play a role in determining when a phase change occurs?

Answer 2

the amount of compound

Question 3

What are intermolecular forces?

Answer 3

The forces between different molecules of a substance

Question 4

Generally speaking, what is the relationship between the strength of the intermolecular forces within a substance and the boiling point of that substance?

Answer 4

The stronger the intermolecular forces, the higher the boiling point.

Question 5

Suppose 10 joules of energy must be added to a sample to change it from the solid phase to the liquid phase at the same temperature. How much energy must be removed to convert the sample from a liquid back to a solid at the same temperature?

Answer 5

Exactly 10 joules

Question 6

Arrange the following phases of matter in increasing degrees of freedom

Answer 6

Solid, liquid, gas

Question 7

When the temperature of a container of argon at atmospheric pressure is lowered to −186°C, the argon condenses to a liquid. At −189°C, the argon freezes. What force holds the particles of argon together in the condensed phase?

Answer 7

London (dispersion) forces

Question 8

In hydrogen bonding, what is the hydrogen bond acceptor?

Answer 8

A highly electronegative atom with at least one lone pair

Question 9

What happens to the vapor pressure at equilibrium when the volume is increased?

Answer 9

Volume has no effect on equilibrium vapor pressure.

Question 10

Which graph shows the general relationship between vapor pressure and temperature?

Answer 10

-

Question 11

At higher altitudes, liquids boil at a lower temperature. Which statement best describes why?

Answer 11

At higher altitudes, the weight of the atmosphere is less, so the temperature at which the vapor pressure equals the atmospheric pressure is lower

Question 12

What is superheated water?

Answer 12

Water that is heated above the normal boiling temperature at the given pressure

Question 13

Look at these two different phase diagrams. Notice that the boundary between the solid and liquid phases for Substance B has a positive slope (tilts to the right) while the boundary between the solid and liquid phases for Substance A has a negative slope (tilts to the left). Given this information, which of the following statements is true?

Answer 13

For Substance B, there is some temperature at which it is possible to go from gas to liquid to solid by application of pressure

Question 14

Diamond is a covalent network solid. This means that each atom in a crystal of diamond ___________ .

Answer 14

shares electrons with all the surrounding atoms, forming covalent bonds

Question 15

Which of the following is not a characteristic of molecular solids?

Answer 15

Molecular solid crystals are very hard, brittle and have a high melting point

Question 16

Which of the following is not a characteristic of covalent network solids?

Answer 16

Covalent network solids may be held together by dipole-dipole forces, hydrogen bonds, or London dispersion forces.

Question 17

Which of the following is not a characteristic of ionic crystals?

Answer 17

Ionic crystals are good conductors of electricity.

Question 18

X-rays from a copper target (λ = 154 pm) are diffracted at an angle of 14.2° from a crystal of pure silicon. If this is the first-order Bragg pattern, what is the spacing between planes of atoms in silicon?

Answer 18

314 pm

Question 19

Arrange the three types of cubic unit cells in order increasing packing efficiency, starting with the lowest and assuming identical, spherical atoms.

Answer 19

simple cubic, body-centered cubic, face-centered cubic.

Question 20

When crystallized, cobalt has a face-centered cubic unit cell. The cobalt atom has a radius of 125 pm. What is the density of cobalt? (Avogadro’s number is 6.023 × 10^23 atoms / mole)

Answer 20

8.81 g / cm^3