Deck 8: Effects of Intermolecular Forces

Question 1

Understand the effects of intermolecular forces on condensation, vapourization, and melting and boiling points.

Answer 1

Attractive intermolecular forces are responsible for the condensation of gases and the freezing of liquids.

Question 2

Predict the relative magnitudes of intermolecular forces and their effects on physical properties of substances.

Answer 2

All intermolecular forces are electrostatic and under most conditions are attractive. Intermolecular forces exist among all ions, dipoles, and uncharged non-polar species. A dipole can be induced into a non-polar species by an ion or by a polar species. Hydrogen bonds exist among species having a polar bond between H and O, N, or F.

Question 3

Explain trends in surface tension, capillary action, viscosity, and vapour pressure in terms of intermolecular forces.

Answer 3

Substances with higher intermolecular forces have higher surface tensions, higher viscosities, and lower vapour pressures.

Question 4

Explain the properties of solids in terms of the dominant intermolecular forces present.

Question 5

Understand amorphous and crystalline solids at the molecular level.

Question 6

Explain enthalpies of phase changes in terms of intermolecular forces and interpret a pressure-temperature phase diagram of a pure substance.

Question 7

Which of the following experience the strongest intermolecular forces?

A) F₂
B) I₂
C) Br₂
D) Cl₂

Question 8

Which of the following is a liquid under normal atmospheric conditions of temperature and pressure?

A) F₂
B) I₂
C) Br₂
D) Cl₂

Question 9

Which of the following experience the strongest covalent bond?

A) F₂
B) I₂
C) Br₂
D) Cl₂

Question 10

Use the following equation for questions


-The relative size of the Van der Waals constant, $\alpha$ , correlates well with boiling point; that is, the larger $\alpha$ is, the higher the boiling point. The reason for this correlation is

A) the $\alpha$ constant is a measure of molecular size.
B) the boiling point is directly proportional to $\alpha$ .
C) the $\alpha$ constant varies with temperature.
D) the $\alpha$ constant is a measure of intermolecular force strength.
E) the $\alpha$ constant varies with vapour pressure.

Question 11

Use the following equation for questions


-The value "nb" that is used in the Van der Waals equation accounts for what INCORRECT assumption?

A) that gaseous collisions are not completely elastic
B) that gas molecules do take up space
C) that gas molecules interact with each other
D) that gas molecules do not travel in straight lines
E) that the velocity of gas molecules changes with temperature

Question 12

Where would you expect Ne to appear in the following sequence of boiling points?
He < H₂ < N₂ < F₂ < Ar < O₂

A) lower than He
B) between He and H₂
C) between H₂ and N₂
D) between F₂ and Ar
E) between Ar and O₂

Question 13

Which of the following is the expected order of boiling points for H₂, He, F₂ and Ne?

A) H₂ < He < F₂ < Ne
B) H₂ < F₂ < Ne < He
C) Ne < H₂ < He < F₂
D) He < H₂ < F₂ < Ne
E) He < H₂ < Ne < F₂

Question 14

Which is the most realistic picture for a container of Ar(l)?

A)

B)

C)

D)

E)

Question 15

Consider the following three molecules: The dominant intermolecular force acting in each is, respectively ,

A) dipole-dipole; dipole-dipole; hydrogen bonding.
B) hydrogen bonding; dispersion forces; dipole-dipole.
C) hydrogen bonding; ion-ion; dipole-dipole.
D) hydrogen bonding; dipole-dipole; dispersion forces.
E) dipole-dipole; dipole-dipole; dipole-dipole.

Question 16

Which is the expected order of increasing boiling point for the following molecules?

A) 1, 2, 3
B) 1, 3, 2
C) 3, 2, 1
D) 2, 1, 3
E) 2, 3, 1

Question 17

Acetone CH₃COCH₃ boils at a significantly higher temperature than 2-methylpropane isobutene

A) because dipole-dipole forces are always greater than dispersion forces.
B) because the molecular mass of acetone is slightly less than that of 2-methylpropane.
C) because the density of acetone is greater than that of 2-methylpropane.
D) because the attractive dispersion forces in 2-methylpropane are weaker than those in acetone.
E) because the attractive dispersion forces in 2-methylpropane are weaker than the dipole forces in acetone.

Question 18

The boiling point of HCl (188 K) is lower than that for HI (238 K) because

A) HI is more polar therefore the intermolecular dipole-dipole forces are stronger in HI.
B) HCl is more polar therefore the intermolecular dipole-dipole forces are stronger in HI.
C) the molecular mass of HI is greater than that of HCl.
D) HI is more polarizable, dispersion forces compensate for the lower dipole forces in HI.
E) HI is capable of hydrogen bonding, HCl is not.

Question 19

In which of the following pure substances will hydrogen bonding be an important intermolecular force? 1) dichloromethane, CH₂Cl_2, 2) CH₃CH₂OH, 3) methylamine, (CH₃NH₂), 4) trimethylamine, N(CH₃)₃

A) 2 and 3
B) all
C) none
D) 1 and 2
E) 3 and 4

Question 20

List the following three compounds in order of increasing boiling point:

A) 1, 2, 3
B) 3, 2, 1
C) 1, 3, 2
D) 2, 1, 3
E) 2, 3, 1

Question 21

What is the dominant intermolecular force for acetylcetone?

A) hydrogen bonding
B) dipole interactions
C) dispersion
D) ionic
E) none of these

Question 22

What is the dominant intermolecular force for propionic acid?

A) hydrogen bonding
B) dipole interactions
C) dispersion
D) ionic
E) none of these

Question 23

Arrange the following molecules in order of increasing viscosity:
1) CH₄,
2) CH₃CH₂C(H)=CH₂,
3) CH₃CH₂C(CH₃)₃,
4) CH₃CH₂CH₂CH₂CH₂CH₃

A) 4 < 3 < 2 < 1
B) 2 < 1 < 4 < 3
C) 1 < 2 < 4 < 3
D) 1 < 4 < 3 < 2
E) 3 < 1 < 2 < 4

Question 24

Which of the following will have the lowest viscosity?

A) nonane
B) octane
C) pentane
D) heptane
E) hexane

Question 25

Arrange the following in order of increasing vapour pressure at room temperature.
1) CH₃OCH₃,
2) CH₃CH₂OCH₂CH₃,
3) CH₃C(O)CH₃,
4) CH₃CH₂OH

A) 2 < 3 < 1 < 4
B) 1 < 4 < 3 < 2
C) 4 < 3 < 2 < 1
D) 3 < 4 < 1 < 2
E) 4 < 1 < 2 < 3

Question 26

Arrange the following in order of increasing vapour pressure at room temperature:
1) H₂O,
2) Hg,
3) Br₂,
4) CH₃CH₂OH

A) 2 < 3 < 1 < 4
B) 1 < 4 < 3 < 2
C) 4 < 3 < 2 < 1
D) 4< 3< 1 < 2
E) 2 < 1 < 4 < 3

Question 27

Arrange the following in order of decreasing surface tension at room temperature:
1) H₂O,
2) Hg,
3) benzene,
4) n-hexane

A) 2 < 3 < 1 < 4
B) 1 < 4 < 3 < 2
C) 2 < 1 < 3 < 4
D) 4< 3< 1 < 2
E) 2 < 1 < 4 < 3

Question 28

For the following substances determine which of the selections is arranged in order of increasing expected melting point:

A) 1 < 3 < 2 < 4
B) 1 < 4 < 3 < 2
C) 2 < 3 < 4 < 1
D) 3 < 4 < 2 < 1
E) 3 < 2 < 4 < 1

Question 29

For the following substances, choose the answer which best describes what type of solid will form, respectively, upon solidification:

A) ionic, network, ionic, metallic
B) ionic, molecular, molecular, metallic
C) network, molecular, ionic, network
D) network, molecular, ionic, metallic
E) network, ionic, ionic, metallic

Question 30

For the following substances, choose the answer which best describes what type of solid will form respectively, upon solidification:

A) ionic, metallic, ionic, network
B) ionic, molecular, molecular, metallic
C) network, metallic, molecular, ionic
D) molecular, metallic, ionic, molecular
E) ionic, metallic, molecular, ionic

Question 31

For the following substances, choose the answer which best describes what type of solid will form respectively, upon solidification:

A) molecular, ionic, molecular, ionic
B) metallic, molecular, molecular, ionic
C) network, metallic, molecular, ionic
D) molecular, network, ionic, ionic
E) molecular, ionic, network, ionic

Question 32

Your solid is non-conductive and melts at relatively low temperature. Based on this information, one can conclude that bonding in the solid is most likely

A) metallic.
B) covalent.
C) molecular covalent.
D) ionic.
E) polar covalent.

Question 33

You have a non-conductive solid. On melting at 30^oC, it forms a conductive liquid. It is soluble in water, and when dissolved, the aqueous solution is conductive. Based on this information one can conclude that bonding in the solid is most likely

A) metallic.
B) covalent.
C) molecular covalent.
D) ionic.
E) polar covalent.

Question 34

You have a solid that it characterized by high melting and boiling points, is NOT conductive, and does NOT dissolve in water. Bonding is most likely

A) metallic.
B) covalent.
C) molecular covalent.
D) ionic.
E) polar covalent.

Question 35

Metals are ductile (can be drawn into wires) and malleable (forced into thin sheets by hammering) because

A) bonding is omnidirectional.
B) bonding is by directed covalent bonds.
C) they are good electrical conductors.
D) they have partially filled bonding bands.
E) they have a range of melting points.

Question 36

30 In the simple cubic crystal structure at right, the unit cell is outlined in heavy lines which intersect to form the corners at the center of the spheres. If the corners of the unit cells are at the center of the spheres, how many atoms are in one unit cell?

A) 1
B) 2
C) 3
D) 4
E) 6

Question 37

The face-centered cubic unit cell to the right has been shaded to add clarity; the balls in the corners are black: those in the faces are gray. If the corners of the unit cells are at the center of the corner spheres, how many atoms are in one unit cell?

A) 1
B) 2
C) 3
D) 4
E) 6

Question 38

Ruby is a crystalline compound that contains aluminum, oxygen and chromium. The structure of ruby is best described as having

A) amorphous structure.
B) interstitial defects.
C) substitutional defects.
D) a and c
E) a and b

Question 39

Which type of solid is the most densely packed?

A) simple cubic
B) face-centered cubic
C) body-centered cubic
D) amorphous solid
E) density is the same for all

Question 40

Below is the structure for zinc sulphide. If the zinc atoms (zinc) are contained within the unit cell and the sulphur atoms (clear) form a face-centered cubic structure, how many sulphur atoms must be contained within the unit cell to balance the charge?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 41

Polonium metal crystallizes in a simple cubic structure. If the atomic radius of polonium is 160 pm, what is the volume of a unit cell?

A) 3.28x10^-23 cm³
B) 4.10 x 10^-29 m³
C) 4.10 x10⁶ pm³
D) 3.28 x 10^-6 m³
E) 3.28 x 10^-23 m³

Question 42

Na⁺ has an ionic radius of 116 pm and Cl^- an ionic radius of 167 pm. Estimate the volume of a NaCl unit cell.

A) 1.81 x 10^-4 m³
B) 2.27 x 10^-29 m³
C) 1.81x10^?28 m³
D) 3.73 x10^-29 m³
E) 2.27 x 10⁷ pm³

Question 43

Use the phase diagram of oxygen to determine the phases oxygen passes through starting at 0.001 atm and 100^oK, cooling and increasing the pressure steadily to 25 K at 1 atm.

A) gas, liquid
B) liquid, solid
C) gas, liquid, solid
D) liquid, solid, gas
E) gas, solid

Question 44

What feature makes the phase diagram of water unusual?

A) The boiling point is high.
B) The positive slope of the liquid-gas equilibrium line.
C) The positive slope of the solid-liquid equilibrium line.
D) The negative slope of the liquid-gas equilibrium line.
E) The negative slope of the solid-liquid equilibrium line.

Question 45

The order of increasing melting point for several simple molecular compounds is: H₂, F₂, O₂, N₂, Ar, while for these same compounds boiling point increases as H₂, N₂, F₂, Ar, O₂. Explain why the trends for boiling point and melting point are different.

Question 46

A sample of 1.5 moles of CO₂ (a = 3.59 atm•L²/mol²; b = 0.0427 L/mol) is contained in a cylinder of 100 mL volume at a temperature of 350^oK. What is the percent deviation from ideal behaviour?

Question 47

A tank of nitrogen in a lab contains about 125 moles of N₂ (a = 1.39 atm•L²/mol²; b = 0.0391 L/mol) in a volume of 20 L. Calculate the percent deviation from ideal behaviour at 298^oK.

Question 48

Some believe that differences between boiling points are truer indicators of relative intermolecular forces than melting points. Why?

Question 49

Draw molecular pictures that illustrate and explain the different polarizabilities of CH₂Cl₂ and CHCl₃.

Question 50

Of the following pairs, select the pair that undergoes hydrogen bonding and draw a molecular picture of the hydrogen bond interaction.
1. NaCl and acetone, (CH₃)₂CO
2. CH₃OCH₃ and CF₃Cl
3. NH₃ and CCl₄
4. NF₃ and CF₄
5. CH₃NH₂ and CH₃OCH₃

Question 51

Draw how water can hydrogen bond with itself.

Question 52

For the three molecules whose structures and boiling points are shown below, explain the trend in boiling points in terms of the strength and types of intermolecular forces acting between the molecules in the pure liquids.

Question 53

Which of the following molecules will have the greatest surface tension and why?
1) methanol, CH₃OH
2) gasoline, ~C₈H₁₈
3) diethyl ether, CH₃CH₂OCH₂CH₃.

Question 54

Describe how trees are able to transport water from their roots to the leaves on their branches high in the air.

Question 55

The leaves of the lotus plant are extremely hydrophobic. That is, water does not stick to the leaves. In 2004, scientists were able to replicate this phenomenon on a film. Sketch what you think the meniscus of water would look like in a tube made of this material? What would the meniscus look like for oil?

Question 56

Explain why water "beads" up on waxed surfaces, but oil spreads out on the same surface?

Question 57

Which will have the highest vapour pressure at standard condition and explain why.
1. 1-hexanol, C₆H₁₃OH
2. benzene, C₆H₆
3. hexane, C₆H₁₄

Question 58

What are the differences in interparticle forces for network and metallic solids?

Question 59

List at least two different physical properties between network and molecular solids.

Question 60

What are the differences in interparticle forces for metallic and ionic?

Question 61

The figure shows the unit cell of a compound containing A (open spheres) and X (shaded spheres). What is the empirical formula of this compound if the shaded spheres form a face-centered cubic arrangement and the open spheres are contained within the unit cell?

Question 62

What is the main difference between an amorphous solid and a crystalline solid?

Question 63

Cesium chloride forms a body-centered cubic solid. One of the elements is in the middle; the other is on each corner of the cube. Which element is in each location and why?

Question 64

Oxygen is an important component of the atmosphere. Draw the phase diagram for O₂ given the normal melting point (-218°C), the normal boiling point (-183°C) and the triple point (-219°C and 1.10 mm Hg.

Question 65

Use the phase diagram of oxygen to estimate the temperature at which liquid oxygen will boil under 0.5 atm external pressure and compare that to the normal boiling point.

Question 66

Sketch a phase diagram for hydrazine locating all points given: normal melting point (1.4˚C), normal boiling point (113.5˚C), critical point (380˚C, 145 atm), triple point (2.0˚C, 3.4 mm Hg)

Question 67

Sketch the phase diagram for benzene identifying the solid, liquid, and gas phases given the following: normal boiling point (80.1˚C), triple point (5.5˚C, 35.8 mm Hg), critical point (288.5˚C and 47.7 atm)

Question 68

Define supercritical fluid and how to make such a fluid.

Question 69

To melt or vapourize a substance, a certain amount of energy needs to be supplied. These are referred to as the heat of fusion and heat of vapourization. Which is typically a lot larger and why?

Question 70

How much energy is required when 23 grams of ethanol at 30˚C are vapourized from a "flaming" desert? ΔH˚_vap = 39.3 kJ/mol, T_vap = 351 K, ΔH˚_fus = 7.61 kJ/mol, T_fus = 156 K, C_ethanol = 112 J/mol˚C

Question 71

How much energy is required when 23 grams of ice at -4?C are melted in a 240 ml glass of pop? ?H?_vap = 40.7 kJ/mol, ?H?_fus = 6.0 kJ/mol, C_ice = 37.8 J/mol?C, C_water = 75.3 J/mol?C