Honors Chemistry
Name _____________________________________
Chapter 10: Forces of Attraction, Phase Change,
and Solids Answer Key
Date _____/_____/_____
Period_____
1. What is a dipole-dipole attraction? What is hydrogen bonding?
Dipole-dipole attractions occur because oppositely charged ends (positive and negative ends)
of different molecules attract one another like little magnets.
Hydrogen bonding is the strongest type of intermolecular force. It occurs when the highly
electronegative elements N, O, F bond with H. These attractions are stronger because as N,
O, and F pull the bonding electrons closer to themselves all that is remaining on the H side of
the compound is a “naked” proton. This causes the N, O, or F side to be greatly negative and
the H side to be extremely positive.
2. How do the strengths of dipole-dipole forces compare with the strengths of typical covalent bonds?
All intermolecular forces are significantly weaker than intramolecular forces; this includes
dipole-dipole (an intermolecular force) and covalent bond (an intramolecular force).
3. Explain how London dispersion forces arise. Although London dispersion forces exist among all
molecules, for what type of molecules are they the only major intermolecular forces? Are London
dispersion forces relatively strong or relatively weak? Explain.
All molecules have the potential for the formation of London forces, however, these
are the only types of IMF that occurs in a non-polar covalent molecules, Noble
gases, and nonmetal atoms. LDF result from the movement of electrons outside of its
normal orbit which generates temporary positive and negative regions in the
molecule.
4. How do intermolecular forces affect each of the following?
a. When intermolecular forces increase the boiling point increases.
b. When intermolecular forces increase the melting point increases.
c. When intermolecular forces increase vapor pressure decreases.
d. Solubility – substances with like intermolecular forces dissolve in one another – “Like
Dissolves Like”.
e. Adhesive forces – two different substances attract due to like intermolecular forces.
(Example: water in a graduated cylinder)
f.
Cohesive forces – two different substances do not attract due to unlike intermolecular
forces. (Example: mercury in a graduated cylinder)
5. What causes dipole-dipole interactions?
a. unequally sharing of electron pairs
b. bonding of a covalently-bonded hydrogen to an lone electron pair
c. the random motion of electrons
d. none of these
6. Why is hydrogen bonding only possible with hydrogen?
a. Hydrogen is the least electronegative element known.
b. The size of a hydrogen atom is similar to that of oxygen, nitrogen, and fluorine.
c. Hydrogen is the only atom with an unshielded nucleus when it forms covalent bonds.
d. More than one of the above.
7. Which of the following is the weakest attractive force?
a. polar covalent bond
c. ionic bond
b. hydrogen bond
d. dipole-dipole force
8. What is the strongest intermolecular / intramolecular force present for each of the following
compounds? Drawing the geometric structures can help to determine the type of intermolecular
forces.
a. water
Hydrogen bonding
b. carbon tetrachloride
London dispersion forces
c. ammonia
Hydrogen bonding
d. carbon dioxide
London dispersion forces
e. phosphorus trichloride
Dipole-dipole forces
f. nitrogen
London dispersion forces
g. ethane (C2H6)
London dispersion forces
h. acetone (CH3COCH3)
Dipole-dipole forces
i. methanol (CH3OH)
Hydrogen bonding
j. borane (BH3)
LDF
9. Circle all the compounds in the following list that would be expected to form intermolecular
hydrogen bonds in the liquid state:
a.
b.
c.
d.
e.
f.
CH3OCH3 (dimethyl ether)
CH4
HF
CH3CO2H (acetic acid)
Br2
CH3OH (methanol)
10. Specify the predominant force of attraction that would affect the boiling point of the compound
and list it immediately following the substance. Then in the last column, indicate which member of
the pair you would expect to have the higher boiling point. Possible forces of attraction are:
metallic bonding, ionic bonding, network covalent bonding, hydrogen bonding, dipole-dipole and
London dispersion forces
Substance
#1
a. HCl(l)
Predominant
Intermolecular
Force
Dipole-dipole
Substance
#2
I2
Predominant
Intermolecular
Force
LDF
Substance with
Higher Boiling Point
b. CH3F
Dipole-dipole
CH3OH
Hydrogen bonding
CH3OH
c. H2O(l)
Hydrogen bonding
H2S
Dipole-dipole
H2O(l)
d. SiO2(s)
SO2
Dipole-dipole
SiO2(s)
e. Fe(s)
Network covalent
bonding
Metallic Bonding
Kr
LDF
Fe
f. CH3OH(l)
Hydrogen bonding
CuO(s)
Ionic bonding
CuO
g. NH3
Hydrogen bonding
CH4
LDF
NH3
Dipole-dipole
NaCl
Ionic bonding
NaCl
Network covalent
bonding
Cu(s)
Metallic Bonding
SiC
h. HCl(g)
i.
SiC
HCl(l)
11. What must be overcome to melt or vaporize a substance? Explain.
The forces of attract between the molecules must be at least partially overcome in order for a
substance to change state. These forces of attraction are typically intermolecular forces.
12. Define the equilibrium vapor pressure of a liquid. How is the magnitude of a liquid’s vapor pressure
related to the intermolecular forces?
Equilibrium vapor pressure is the pressure caused by the equilibrium of the liquid vaporizing
and the gas condensing in a closed system. This is affected by the tendency of the liquid to
vaporize and the tendency to vaporization is determined by the strength of the intermolecular
forces.
13. How do we know that the properties of the solid and the liquid states of a substance are more similar
than to the properties of the substance in the gaseous state?
Solids and liquids are more similar because of the interaction of the particles (intermolecular
Forces). The particle of solids and liquids interact more identically then particles of liquids
and gases because solids and liquids have similar IMF of attraction.
14. Explain how the process of vaporization and condensation represent equilibrium in a closed
container.
At constant temperature, the liquid is going to the gaseous phase or state at the same rate
that the gas is going to the liquid phase or state.
15. What is the effect of a dishwashing liquid on the surface tension of water? Explain.
Dishwashing liquid decreases the surface tension of water because the intermolecular forces
of the soap are different than the intermolecular forces of water. Because the forces of
attraction are different, the addition of the soap weakens the attraction that typically occurs
between the water molecules.
Phase Diagram
For each of the questions on this worksheet, refer to the phase diagram for mysterious compound X.
16. What is the critical temperature of compound X? ~770 oC
17. If you were to have a bottle containing compound X in your closet, what phase would it most likely
be in?
Extrapolating from this diagram, it’s most likely a gas.
18. At what temperature and pressure will all three phases coexist? 350 oC, ~51 atm
19. If I have a bottle of compound X at a pressure of 45 atm and temperature of 100 oC, what will happen
if I raise the temperature to 400 oC? It will sublime
20. Why can’t compound X be boiled at a temperature of 200 oC?
It does not form a liquid at this temperature. It only exists as a liquid at temperatures above
350 oC.
21. If I wanted to, could I drink compound X?
No. At the temperatures and pressures that it forms a liquid, you’d probably die.
22. What observable difference would there be for the solid/liquid line for the phase diagram for
compound X and the phase diagram for water? Why? Refer to your notes/book for a phase
diagram of water. The solid / liquid line for compound X angles to the right because the
density of the solid state of compound X is denser then the liquid state of
compound X. The solid liquid line for water would angle to the left because
the density of the solid state of water is less dense then the liquid state of
water.
23. What is vaporization? What is condensation?
Vaporization – it is a substance changing from a liquid phase to a gaseous phase
Condensation – it is a substance changing from a gaseous phase to a liquid phase.
24. Define molar heat of fusion and molar heat of vaporization.
The amount of heat (energy) needed to melt (go from a solid to a liquid phase) 1.00 mole of a
substance at its melting point.
The amount of heat (energy) needed to vaporize 1.00 moles a substance at its boiling point.
25. The heat of fusion of aluminum is 3.95 kJ/g. What is the molar heat of fusion of aluminum?
3.95 kJ Al
g
│
│
26.98 g Al
1 mole Al
= 107 kJ/mole
26. Calculate the total energy required to convert 55.1 grams of ice at 0.00 oC to a resulting gaseous
state at 100. oC.
S(solid) = 2.1 J/g oC
H fusion
= 6.02 kJ/mole
o
S(liquid) = 4.2 J/g C
H vaporization
= 40.7 kJ/mole
S(vapor) = 2.1 J/g oC
(55.1 grams)(1 mole / 18.02 g) = 3.06 moles
H fusion X moles
(6.02 kJ/mole)( 3.06 moles) = 18.4 kJ
Q=sm T
(4.2 J/g oC)(55.1 grams) (100. oC) = 23,000 J = 23 kJ
H vaporization X moles
(40.7 kJ/mole)( 3.06 moles) = 125 kJ
18.4 kJ
23 kJ
+ 125 kJ
166 kJ
27. Draw a heating / cooling curve for iron, which has a melting point of 1535 oC and a boiling
point of 2750 oC. Make sure to properly label both axis of your graph.
Types of Solids
28. Crystalline solid – a solid characterized by the regular arrangement of its components.
29. List some properties of each of the following.
a.
Ionic solids – components are ions. (NaCl)
- Ionic bonds
- High melting and boiling points
- Hard and brittle
- Do not conduct electricity
b.
Molecular solids – components are molecules. (Sucrose – C12H22O11)
- D-D, H. Bonding, and/or LDF
- Medium to Low melting and boiling points
- Soft / hard
- Do no conduct electricity (used as insulators)
c.
Atomic solids – components are atoms.
- Network Atoms
- Compounds containing Si and C(diamond)
- Covalent bonds
- Hard
- High melting and boiling points
- Insulators
- Metals
- delocalized electrons (sea of electrons)
- soft to hard
- Various melting points
- Conduct heat and electricity
- Noble gases
- LDF
- Low melting and Boiling points
- Gases
d.
Alloy – a substance that contains a mixture of elements and has metallic properties.
- substitutional alloy – metal atoms are replaced by other metal atoms of similar
size.
- Interstitial alloy – are formed when some of the holes are filled by smaller atoms.