Deck 12: Intermolecular Forces and Liquids

Question 1

Which of the following bonds can potentially form a hydrogen bond in a solid or liquid phase?

A) Cl-H
B) Si-H
C) N-H
D) I-H
E) Br-H

Answer 1

N-H

Question 2

Which one of the following statements is false?

A) All ions are hydrated in aqueous solution.
B) All cations are hydrated in aqueous solution.
C) All anions are hydrated in aqueous solution.
D) Hydration is generally highly endothermic for ionic compounds.
E) The heats of hydration of cations increases as their charge-to-radius ratios increase.

Answer 2

Hydration is generally highly endothermic for ionic compounds.

Question 3

Which one of the following molecules will exhibit dipole-dipole intermolecular forces as a pure liquid or solid?

A) CSe₂
B) C₂H₂
C) SiF₄
D) O₂
E) PF₃

Answer 3

PF₃

Question 4

When a water molecule forms a hydrogen bond with another water molecule, which atoms are involved in the interaction?

A) a hydrogen from one molecule and a hydrogen from the other molecule
B) a hydrogen from one molecule and an oxygen from the other molecule
C) an oxygen from one molecule and an oxygen from the other molecule
D) an oxygen and a hydrogen from the same molecule
E) two hydrogens from one molecule and one hydrogen from the other molecule

Question 5

As pure molecular solids, which of the following exhibits dipole-dipole intermolecular forces: HBr, NBr₃, SBr₂, and CBr₄?

A) HBr only
B) CBr₄ only
C) HBr and SBr₂
D) NBr₃ and CBr₄
E) HBr, NBr₃, and SBr₂

Question 6

Hydrogen bonding is present in all of the following molecular solids EXCEPT ____.

A) H₂SO₄ (dihydrogen sulfate)
B) CH₃OH (methanol)
C) CH₃OCH₃ (dimethyl ether)
D) HF (hydrogen fluoride)
E) CH₃CO₂H (acetic acid)

Question 7

Place the following cations in order from the most negative to the least negative hydration enthalpy: Li⁺, H⁺, and K⁺.

A) K⁺ < Li⁺ < H⁺
B) K⁺ < H⁺ < Li⁺
C) H⁺ < Li⁺ < K⁺
D) H⁺ < K⁺ < Li⁺
E) Li⁺ < H⁺ < K⁺

Question 8

Which of the following substances will have the strongest intermolecular forces?

A) H₂S
B) CO
C) CH₃OH
D) HBr
E) Rn

Question 9

A molecule will always be polar if it ___.

A) has polar bonds
B) contains both carbon and chlorine
C) consists of more than three atoms
D) is diatomic with different electronegativities
E) contains atoms with different electronegativities

Question 10

Which of the following strong electrolytes has the most negative hydration enthalpy?

A) NaCl
B) KCl
C) RbCl
D) CsCl
E) HCl

Question 11

Which of the following pure liquids is expected have the highest boiling point?

A) CO
B) NO
C) PH₃
D) AsH₃
E) ICl

Question 12

Which intermolecular force or bond is responsible for the density of
H₂O(s) being less than that of H₂O( $\ell$ )?

A) London dispersion forces
B) hydrogen bonding
C) ionic bonding
D) covalent bonding
E) dipole/induced dipole forces

Question 13

Arrange HF, HCl, and HBr in increasing order of their boiling point.

A) HF < HCl < HBr
B) HF < HBr < HCl
C) HBr < HF < HCl
D) HBr < HCl < HF
E) HCl < HBr < HF

Question 14

As pure molecular solids, which of the following exhibits dipole-dipole intermolecular forces: PH₃, SO₃, HCl, and CO₂?

A) PH₃ only
B) HCl only
C) SO₃ and CO₂
D) PH₃ and HCl
E) SO₃, HCl, and CO₂

Question 15

Arrange the following cations in the increasing order their enthalpy of hydration:
K⁺, Ca²⁺, and Mg²⁺.

A) K⁺ < Ca²⁺ < Mg²⁺
B) Mg²⁺ < Ca²⁺ < K⁺
C) Ca²⁺ < K⁺ < Mg²⁺
D) Ca²⁺ < Mg²⁺ < K⁺
E) Mg²⁺ < K⁺ < Ca²⁺

Question 16

The elements of group 5A, the nitrogen family, form compounds with hydrogen having the boiling points listed below:
SbH₃, -17 °C; AsH₃, -55 °C; PH₃, -87 °C; and NH₃, -33 °C
The first three compounds illustrate a trend where the boiling point decreases as the mass decreases; however, ammonia (NH₃) does not follow the trend because of _____.

A) debye forces
B) metallic bonding
C) hydrogen bonding
D) London dispersion forces
E) ionic bonding

Question 17

Which one of the following sets of ions are listed in order of lowest to highest hydration energy?

A) H⁺ < Na⁺ < Mg²⁺
B) Mg²⁺ < Ca²⁺ < Ba²⁺
C) Mg²⁺ < Ba²⁺ < Ca²⁺
D) Ca²⁺ < K⁺ < Rb⁺
E) Rb⁺ < K⁺ < Ca²⁺

Question 18

Arrange H₂S, H₂Se, and H₂Te in order from lowest to highest boiling point.

A) H₂Te < H₂Se < H₂S
B) H₂S < H₂Se < H₂Te
C) H₂S < H₂Te < H₂Se
D) H₂Se < H₂Te < H₂S
E) H₂Te < H₂S < H₂Se

Question 19

Consider the following molecules: ethanol (CH3CH2OH), acetic acid (CH3CO2H), acetaldehyde (CH3CHO), and dimethyl ether (CH3OCH3). Which of these molecules is/are expected to form hydrogen bonds in the liquid or solid phase?

A) Ethanol only
B) Acetaldehyde only
C) Ethanol and acetic acid
D) Acetaldehyde and dimethyl ether
E) Ethanol and dimethyl ether

Question 20

Which of the following statements best describes what happens when a small amount of solid potassium chloride is dissolved in water?

A) The heat from the warm water melts the solid, making it a liquid.
B) Nothing happens, because potassium chloride is insoluble in water.
C) The solid KCl breaks apart into separate K and Cl atoms by interacting with the water molecules.
D) The water molecules surround each ion in the solid KCl, separating the K ions from the Cl ions.
E) The solid undergoes a chemical change by reacting with the water.

Question 21

Which of the following intermolecular forces or bonds is primarily responsible for the solubility of methanol ( CH₃OH) in water?

A) Ion-dipole force
B) Debye force
C) Ionic bonding
D) Covalent bonding
E) Hydrogen bonding

Question 22

Which of the following nonpolar molecules has the highest boiling point?

A) N₂
B) C₂H₄
C) F₂
D) O₂
E) CS₂

Question 23

Which of the following liquids has the lowest enthalpy of vaporization?

A) C₄H₁₀
B) C₅H₁₂
C) C₆H₁₄
D) C₇H₁₆
E) C₈H₁₈

Question 24

As pure molecular solids, which of the following exhibit only induced dipole/induced dipole forces: CO₂,
CH₂Cl₂, and SO₂?

A) CO₂ only
B) CH₂Cl₂ only
C) SO₂ only
D) CO₂ and CH₂Cl₂
E) CO₂ and SO₂

Question 25

For which of the following pure solids is it necessary to break covalent bonds to make a liquid or gas: C(graphite), CO₂(s), C₆₀(s), and C(diamond)?

A) C(graphite) only
B) CO₂(s) only
C) CO₂(s) and C₆₀(s)
D) C(graphite), C₆₀(s) and C(diamond)
E) C(graphite) and C(diamond)

Question 26

The vapor pressure of a given liquid will increase if

A) the liquid is moved to a container in which its surface area is very much larger.
B) the volume of the liquid is increased.
C) the temperature is increased.
D) the volume of the vapor phase is increased.
E) a more volatile liquid is added to the given liquid.

Question 27

London dispersion forces are the only significant factor affecting boiling point for all the following except?

A) Kr
B) NH₃
C) CBr₄
D) Cl₂
E) CH₄

Question 28

Which of the following liquids would you expect to have the lowest vapor pressure at room temperature?

A) Ethylene glycol (bp, 198°C)
B) Benzene (bp, 80°C)
C) Ethanol (bp, 78.3°C)
D) Chloroform (bp, 62°C)
E) n-pentane (bp, 36.1°C)

Question 29

Which of the following is the strongest intermolecular force present in NH₃?

A) London dispersion
B) Hydrogen-bonding
C) Debye force
D) Ion-dipole
E) None of these

Question 30

The normal boiling points of some group 7A hydrides are tabulated below. $$\begin{array} { l l } \text { Gas } & \mathrm { BP } \left( { } ^ { \circ } \mathrm { C } \right) \\\hline \mathrm { HF } & 19.7 \\\mathrm { HCl } & - 84.8 \\\mathrm { HBr } & - 66.4\end{array}$$
Which of the following intermolecular forces or bonds is responsible for the high boiling point of HF relative to HCl and HBr?

A) Hydrogen bonding
B) Dipole-induced dipole force
C) Induced dipole-induced dipole force
D) Covalent bonding
E) Ion-induced dipole force

Question 31

Which of the following molecules has the lowest boiling point?

A) CH₄
B) CHCl₃
C) CH₂Cl₂
D) CH₃Cl
E) CCl₄

Question 32

Ammonia (NH₃) is used as a refrigerant. At its boiling point of -33 °C, the standard enthalpy of vaporization of ammonia is 23.3 kJ/mol. How much heat is released when 50.0 g of ammonia is condensed at -33 °C?

A) -0.466 kJ
B) -7.94 kJ
C) -36.6 × 10³ kJ
D) -68.4 kJ
E) -1.17 × 10³ kJ

Question 33

Arrange Cl₂, ICl, and Br₂ in order from lowest to highest boiling point.

A) Cl₂ < Br₂ < ICl
B) Cl₂ < ICl < Br₂
C) ICl < Cl₂ < Br₂
D) Br₂ < Cl₂ < ICl
E) Br₂ < ICl < Cl₂

Question 34

Which of the following molecules has the lowest boiling temperature?

A) C₄H₁₀
B) C₅H₁₂
C) C₆H₁₄
D) C₇H₁₆
E) C₈H₁₈

Question 35

Equilibrium is established between a liquid and its vapor when

A) the rate of evaporation equals the rate of condensation.
B) equal masses exist in the liquid and gas phases.
C) equal concentrations (in molarity) exist in the liquid and gas phases.
D) all the liquid has evaporated.
E) the liquid ceases to evaporate and the gas ceases to condense.

Question 36

Which of the following compounds has a boiling point closest to that of argon?

A) F₂
B) Cl₂
C) HCl
D) NaF
E) HF

Question 37

On a relative basis, the weaker the intermolecular forces in a substance are,

A) the larger is its heat of vaporization.
B) the more it deviates from the ideal gas law.
C) the greater is its vapor pressure at a particular temperature.
D) the larger is its molar heat capacity as a liquid.
E) the higher is its boiling point.

Question 38

List all the intermolecular forces present in pure acetone.

A) hydrogen bonding only
B) dipole-dipole force only
C) dipole-dipole force and London dispersion forces
D) hydrogen bonding and London dispersion forces
E) hydrogen bonding, dipole-dipole force, and London dispersion forces

Question 39

Which of the following has the greatest boiling point?

A) Cl₂
B) I₂
C) O₂
D) Ar
E) Xe

Question 40

At its boiling point of 58.8 °C, 2.82 kJ of heat is required to vaporize 15.0 g of bromine (Br₂). What is the molar enthalpy of vaporization of bromine?

A) 0.264 kJ/mol
B) 0.188 kJ/mol
C) 30.0 kJ/mol
D) 5.33 kJ/mol
E) 56.76 kJ/mol

Question 41

At 80.0 °C, water has an equilibrium vapor pressure of 355.1 mm Hg. If 4.22 g H₂O is sealed in an evacuated 5.00 L flask and heated to 80.0 °C, what mass of H₂O will be found in the gas phase when liquid-vapor equilibrium is established? Assume any liquid remaining in the flask has a negligible volume. (R = 0.08206 L⋅atm/mol⋅K, 1 atm = 760 mm Hg)

A) 0.689 g
B) 1.45 g
C) 1.67 g
D) 2.77 g
E) 4.22 g

Question 42

Ethanol has an enthalpy of vaporization of 42.3 kJ/mol. The compound has a vapor pressure of 1.00 atm at 78.3 °C. At what temperature is the vapor pressure equal to 0.800 atm? (R = 8.314 J/K ⋅ mol)

A) -83.8 °C
B) -24.4 °C
C) 62.6 °C
D) 73.0 °C
E) 78.0 °C

Question 43

________ is a measure of the degree to which the electron cloud surrounding an atom or molecule can be distorted in an electric field.

Question 44

A particular compound has an enthalpy of vaporization of 29600 J/mol. At 274 K it has a vapor pressure of 103 mmHg. What is its vapor pressure at 309 K? (R = 8.31 J/K·mol; 1 atm = 760 mmHg)

A) 98.6 mmHg
B) 241 mmHg
C) 23.6 mmHg
D) 449 mmHg
E) 107 mmHg

Question 45

The heat of vaporization of benzene (C₆H₆) is 30.7 kJ/mol at its boiling point of 80.1 °C. How much energy in the form of heat is required to vaporize 110 g benzene at its boiling point?

A) 0.279 kJ
B) 3.58 kJ
C) 21.8 kJ
D) 43.2 kJ
E) $3.38 \times 10 ^ { 3 }$ kJ

Question 46

Xenon has an enthalpy of vaporization of 12.6 kJ/mol and a vapor pressure of 1.00 atm at -108.0 °C. What is the vapor pressure of xenon at -148.0 °C? (R = 8.314 J/K⋅mol)

A) 0.053 atm
B) 0.73 atm
C) 0.93 atm
D) 0.99 atm
E) 19 atm

Question 47

A cup of oil takes longer to pour from a glass than a cup of water. A liquid's resistance to flow is referred to as its ________.

Question 48

Freon-113, C₂Cl₃F₃, has an enthalpy of vaporization of 27.0 kJ/mol and a normal boiling point of 48.0 °C. What is the vapor pressure (in atm) of Freon-113 at 22.0 °C? (R = 8.314 J/K⋅mol)

A) 0.21 atm
B) 0.35 atm
C) 0.41 atm
D) 0.46 atm
E) 4.4 atm

Question 49

Sulfur dioxide has a vapor pressure of 462.7 mm Hg at -21.0 °C and a vapor pressure of 140.5 mm Hg at -44.0 °C. What is the enthalpy of vaporization of sulfur dioxide? (R = 8.314 J/K⋅mol)

A) 0.398 kJ/mol
B) 6.33 kJ/mol
C) 14.0 kJ/mol
D) 24.9 kJ/mol
E) 39.8 kJ/mol

Question 50

Which of the following is the slope of the line that illustrates the relationship between the natural logarithm of the vapor pressure of a gas and the reciprocal of its temperature (in kelvin)?

A) $- \frac { R T } { \Delta _ { \text {vap } } H }$
B) $- R \times \Delta _ { \text {vap } } H$
C) T
D) $- \Delta _ { \text {vap } } H$
E) $- \frac { \Delta _ { \text {vap } } H } { R }$

Question 51

Which of the following is not a characteristic of volatile liquids?

A) Volatile liquids are easily vaporized.
B) Volatile liquids have relatively high vapor pressures.
C) Volatile liquids have strong cohesive forces.
D) Volatile liquids have weak intermolecular forces.
E) All of these

Question 52

The vapor pressure of nitric acid is 26.6 mmHg at 10.0 °C and 208 mmHg at 50.0 °C. Using this information, calculate the heat of vaporization (Δ_vapH) of nitric acid. (R = 8.314 J/K ⋅ mol)

A) 25.6 kJ/mol
B) 39.1 kJ/mol
C) 48.4 kJ/mol
D) 225 kJ/mol
E) 566 kJ/mol

Question 53

A liquid has an enthalpy of vaporization of 30.3 kJ/mol. At 262 K it has a vapor pressure of 121 mmHg. What is the normal boiling point of this liquid? (R = 8.314 J/(K· mol))

A) 278 K
B) 302 K
C) 262 K
D) 248 K
E) 231 K

Question 54

In a certain mountain range, water boils at 93°C. What is the atmospheric pressure under these conditions? The enthalpy of vaporization of water at 100°C is 40.7 kJ/mol. (R = 8.314 J/K·mol; 1 atm = 760 mmHg)

A) 2040 mmHg
B) 278 mmHg
C) 591 mmHg
D) 977 mmHg
E) 283 mmHg

Question 55

For a particular liquid, raising its temperature from 331 K to 351 K causes its vapor pressure to double. What is the enthalpy of vaporization of this liquid? (R = 8.314 J/K · mol)

A) 34 kJ/mol
B) 288 kJ/mol
C) 2 kJ/mol
D) 244 kJ/mol
E) 115 kJ/mol

Question 56

Above its critical temperature and pressure, a substance becomes a(n) ________ fluid.

Question 57

The ________ equation relates the equilibrium vapor pressure of a volatile liquid to the molar enthalpy of vaporization at a given temperature.

Question 58

When a glass tube with a small diameter is placed in water, the water rises in the tube. This is known as ________ action.

Question 59

Mount Everest rises to a height of 8.850 × 10³ m above sea level. At this height, the atmospheric pressure is 231 mm Hg. At what temperature (in °C) will water boil at the summit of Mount Everest? The vapor pressure of water at 373 K is 760.0 mm Hg. (Δ_vapH° for H₂O = 40.7 kJ/mol and R = 8.314 J/K ⋅ mol)

A) 4.07 °C
B) 69.0 °C
C) 72 °C
D) 87 °C
E) 364 °C

Question 60

If 4.61 g of water is sealed in an evacuated 3.35 L flask and heated to the normal boiling point of 373 K, what is the pressure in the flask? (R = 0.08206 L⋅atm/mol⋅K)

A) 0.214 atm
B) 0.428 atm
C) 1.00 atm
D) 2.34 atm
E) 42.1 atm

Question 61

Make a sketch to show the hydrogen bonding between two acetic acid molecules (HC₂H₃O₂).

Question 62

Which ion, K⁺ or Ca²⁺, is expected to have the more negative enthalpy of hydration? Why?

Question 63

Which of the following molecules has the highest enthalpy of vaporization?

A) N₂
B) O₂
C) I₂
D) CH₄
E) C₆H₆

Question 64

Two important allotropes of phosphorus are white phosphorus and red phosphorus. White phosphorus, P₄, has a melting point of 44.1 °C and spontaneously reacts with oxygen. Red phosphorus, a network solid, melts at 280 °C and is stable in air. Use your knowledge of intermolecular and intramolecular bonding to explain why these two forms of the same element have such different properties.