Ch 12: Liquids, Solids, and Intermolecular Forces

Question 1

What are intermolecular forces?

Answer 1

The attractive forces that exist among all the particles that compose matter.

Question 2

A sphere is the geometric shape with the lowest _______ ____ to ______ ratio. This shape maximizes their interaction with one another (within the sphere) bc the sphere results in the minimum number of molecules being at the surface of the liquid where fewer interactions occur.

Answer 2

….surface area to volume ratio.

Question 3

What is the molar volume?

Answer 3

The amount of volume occupied by 1 mole of a compound (or element) at a given temperature or pressure. It is given by the molar mass (or molecular weight) divided by the density of the compound/element.

https://www.sciencedirect.com/topics/chemistry/molar-volume

Question 4

Don’t forget that water is atypical, in that its solid form is slightly ____ dense than its liquid form.

Answer 4

less

Question 5

What is the strength of the intermolecular forces relative to thermal energy in each of the following states?

gas
liquid
solid

Answer 5

weak
moderate
strong

Question 6

Propane exists as a gas at room temperature and atmospheric pressure, but it liquifies at pressures exceeding __ atm, which is why you can purchase it in liquid form in a tank.

Answer 6

2.7

Question 7

Which is the strongest of the intermolecular forces?

Answer 7

ion-dipole forces are the strongest types of intermolecular forces

Question 8

Which properties increase in magnitude with increasing strength of intermolecular forces? Check all that apply.
__viscosity
__surface tension
__vapor pressure
__boiling point

Answer 8

x viscosity
x surface tension
__vapor pressure
x boiling point

(all except vapor pressure)

Question 9

In regard to vaporization and vapor pressure, what does the term dynamic equilibrium mean?

Answer 9

that the rate of evaporation = rate of condensation

Question 10

What is vapor pressure?

Answer 10

The pressure of a gas in dynamic equilibrium with its liquid.

p. 516

Question 11

Weak intermolecular forces result in volatile (easily vaporizable) substances with ___ vapor pressures bc the intermolecular forces are easily overcome by thermal energy.

Answer 11

high

p. 516

Question 12

Strong intermolecular forces result in nonvolatile substances with {high or low} vapor pressures at a given temperature.

Answer 12

low

p. 516

Question 13

What is the enthalpy of vaporization?

Answer 13

the heat required to vaporize one mole of a liquid to gas

Question 14

The higher number of atoms in a molecule that can participate in hydrogen bonding, the _______ the intermolecular forces.

Answer 14

stronger

Question 15

The boiling point of a liquid is the temperature at which the liquid’s _____ ________ equals the ________ _________.

Answer 15

vapor pressure
external pressure

p. 517

Question 16

The approximate pressure at the summit of Mount Everest is only 0.32 atm, which makes the boiling point of water only __°C.

Answer 16

78°C

Question 17

With how many other water molecules can a single molecule of water form hydrogen bonds?

Answer 17

4 other water molecules

p. 530

Question 18

What features of water give it a relatively high boiling point?

Answer 18

Its bent geometry and the highly polar nature of the O-H bond results in a molecule with a significant dipole moment.

p. 530

Question 19

Since boiling point increases with increasing strength of intermolecular forces, and since the halogens only have the __________ force (which increases with increasing molar mass), the boiling points of the halogens increase with increasing molar mass. Iodine has the highest molar mass of the halogens in this list, so it has the highest boiling point.

Answer 19

dispersion

Question 20

Which property of a liquid increases with increasing temperature?

surface tension, viscosity, or vapor pressure

Answer 20

vapor pressure

Question 21

What is the gas constant in J/mol K and kJ/mol K?

Answer 21

8. 314 J/mol K
9. 314 x 10^-3 kJ/mol K

Question 22

Phase changes

The process of transformation from a gas directly into the solid state is known as __________.

The opposite process – that is a solid changing into a gas – is known as __________.

Answer 22

deposition

sublimation

Question 23

The transition from a solid to a liquid is known as melting or ______. The opposite of this process is ________, which changes a liquid into a solid. Thus, the freezing point = the ______ point.

Answer 23

fusion

freezing

fusion

Question 24

What does the plateau region at 0°C of a melting/ freezing curve represent?

Answer 24

That a mixture of water and ice always has a temperature of 0°C (at 1 atm pressure).

The key concept is that once the melting point of a solid is reached, additional heating only causes more rapid melting. It does not raise the temperature of the solid above its melting point.

p. 524(?)

Question 25

In general, low temperature and high pressure favor the _____ state, high temperature and low pressure favor the _____ state, and intermediate conditions favor the _____ state.

Answer 25

solid

gas

liquid

p. 528

Question 26

What is unique about the fusion curve for water?

Answer 26

It has a negative slope. In contrast, most substances have a fusion curve with a positive slope because increasing pressure favors the denser state, which for most substances, is the solid state.

p. 529

Question 27

Carbon dioxide does not melt into a liquid at atmospheric pressure. It only forms a liquid above pressures of __ atm.

Answer 27

5.1

Question 28

In a plot of the natural log of the vapor pressure vs the inverse of the temperature (in Kelvin) produces a straight line. What do we know about the slope of this line?

Answer 28

The slope is equal to the negative of the enthalpy of vaporization divided by R (where R = 8.314 J/mol)

Question 29

Which of the following is true about hydrogen bonding? (select all that apply)

a. ) The CH₄CH₄ molecule exhibits hydrogen bonding.
b. ) A hydrogen bond is possible with only certain hydrogen-containing compounds.
c. ) A hydrogen atom acquires a partial positive charge when it is covalently bonded to an F atom.
d. ) A hydrogen bond is equivalent to a covalent bond.
e. ) Hydrogen bonding occurs when a hydrogen atom is covalently bonded to an N, O, or F atom.

Answer 29

b, c, and e are true

Question 30

What is a hydride?

Answer 30

There are different definitions depending on the source you consult. Most generally, it means any of a class of chemical compounds in which hydrogen is combined with another element (from Britannica.com)

Question 31

The hydrides of group 5A (going down the group) are NH₃, PH₃, AsH₃, and SbH₃. Arrange them from highest to lowest boiling point.

Answer 31

NH₃ has the highest boiling point (bc it exhibits hydrogen bonding)

SbH₃

AsH₃

PH₃ (lowest molar mass of the group)

Question 32

In comparing two compounds, the compound with the (stronger/weaker) intermolecular forces will have the HIGHER vapor pressure.

Answer 32

weaker

Question 33

Intermolecular forces determine the physical properties of substances. The viscosity and surface tension of liquids are two such properties. _________ is the resistance of a liquid to flow. _______ _______ is the energy required to increase the surface area of a liquid by a certain amount. The stronger the forces of attraction, the more difficult it is for the molecules to move past one another, thus increasing the viscosity and surface tension of the liquid.

Answer 33

• Viscosity*
• Surface tension*

Question 34

In a clean glass tube, water can generate strong adhesive interactions with glass (because of the dipoles at the surface of the glass). Water experiences ________ forces with glass that are stronger than its cohesive forces, causing it to climb the surface of a glass tube. When grease or oil coats the glass, this interferes with the formation of these adhesive interactions with glass because oils are nonpolar and cannot interact strongly with the dipoles in the water. Without experiencing these strong intermolecular forces with oil, water’s ________ forces will be greater and water will be drawn away from the surface of the tube.

Answer 34

adhesive

cohesive

Question 35

Water is a polar molecule that can hydrogen bond. Glass (SiO₂) cannot hydrogen bond itself (since it has no hydrogen atoms) but it can and does form hydrogen bonds with water utilizing the lone pairs on the ______ atoms in SiO₂ and the hydrogen atoms in H₂O, so water can hydrogen bond with glass at its surface. These strong adhesive forces allow water to climb the tube effectively.

Hexane (C₆H₁₄) is a nonpolar molecule that establishes only weak adhesive forces with the polar glass. Therefore, hexane climbs the glass tube much less effectively than water.

Answer 35

oxygen

Question 36

How can you find the heat of vaporization if you are given a table showing the temperature and pressure at different points?

Answer 36

Take 2 data points from the chart and imagine a plot of 1/Temp on the x-axis, and ln Pressure on the y-axis. Using these 2 points, find the slope by calculating Δy/Δx. (Remember not to use the data points, use the ln of P and 1/T). The slope of the line is equal to the -H_vap/R.

Question 37

The normal boiling point of a liquid is….

Answer 37

…..the temperature at which its vapor pressure equals 1 atm.

p. 518

Question 38

Classify the following phase changes as exothermic processes or endothermic processes.

deposition

sublimation

condensing

vaporizing

melting

freezing

Answer 38

Exothermic: condensing, freezing, deposition

Endothermic: melting, vaporizing, subliming

Question 39

NH₃ has a higher boiling point than CH₄ because…

Answer 39

it is capable of hydrogen bonding.

Question 40

CS₂ has a higher boiling point than CO₂ despite having similar intermolecular forces because…

Answer 40

…it has a larger molar mass.

Question 41

NO₂ has a higher boiling point than CO₂ because…

Answer 41

…NO₂ is a polar molecule, and thus, exhibits dipole-dipole interactions. CO₂ has a linear molecular shape and does not have a net molecular dipole moment.

Question 42

The ion-dipole force occurs when an aqueous solution of _____ ________ is mixed with a polar compound.

Answer 42

ionic compound