Chem 1A
Chapter 10 Exercises
Types of Intermolecular Interactions
Type of Interaction
Examples
London Dispersion
N2, F2, CO2, CH4, etc.
Melting or Boiling
Temperature
Low
Permanent Dipole-Dipole
HCl, HBr, HI, CO, NO, etc.
Moderate
Hydrogen Bonding
H2O, HF, NH3, CH3OH, etc.
Moderate to High
Metallic
Al, Fe, Cu, Zn, etc.
High (Variable)
Covalent Network
Diamond, Sand (SiO2)
Very High
Ionic
LiF, NaCl, MgO, etc.
Very High
Exercise #1:
1.
Identify the primary type of intermolecular interactions in each of the following substances.
CuS
Xe
Li
NH2OH
BF3
Si
2.
Which substance has the higher boiling point, F2 or Cl2; HF or HCl; HCl or NaCl? Explain.
3.
Which substance has the higher boiling point: C3H8 or C4H10; CH3OH or CH3Cl; CH3CH2OH or
HOCH2CH2OH; ethanol (CH3CH2OH) or dimethyl ether (CH3OCH3)? Explain.
4.
Which substance has the higher vapor pressure at any temperature, acetone (CH3COCH3), or ethanol
(C3CH2OH)? Explain.
5.
Which substance has a higher surface tension and viscosity, ethanol (CH3CH2OH) or ethylene glycol
(HOCH2CH2OH)? Explain.
6.
Explain the differences in the boiling temperatures of the following compounds.
HCl (-85oC),
7.
HF (20oC),
TiCl4 (136oC),
CsCl (1290oC),
LiCl (1360oC)
Rank each of the following sets of substances in order of increasing boiling point:
(a) CH4, SiH4, GeH4, SnH4;
(b) NH3, PH3, AsH3, SbH3;
(c) H2O, H2S, H2Se, H2Te;
(d) HF, HCl, HBr, HI;
(e) C2H6, C4H10, C6H14, C8H18;
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Chem 1A
Chapter 10 Exercises
Exercise #2:
Enthalpy of Vaporization:
1.
When 1.75 g of acetone, C3H6O, vaporizes at 298 K, 933 J of heat is absorbed. Calculate the enthalpy
of vaporization, Hvap (in kJ/mol), of acetone at 298 K.
2.
Calculate the total amount of heat (in kJ) absorbed when 45.4 g of ice, initially at –20.0oC, is
completely converted into steam at 120.0oC?
(Specific heat (J/g.oC): ice and steam = 2.0; water = 4.184; Hfus = 6.02 kJ/mol; Hvap = 40.6 kJ/mol)
3.
A sample of ice at 0.0oC is added to 100.0 g of water at 35.0oC. The final temperature of mixture is
18.5oC. Calculate the mass of ice. (Specific heat (J/g.oC) of water = 4.184; Hfus = 6.02 kJ/mol);
4.
The enthalpy of vaporization of Freon (CCl2F2) is 167 kJ/kg at its boiling point (-29.8oC, 1 atm). If
the enthalpy of fusion of water at 0oC is 6.02 kJ/mol, how many grams of Freon must evaporate to
freeze 45.4 g of water at 0oC?
Vapor Pressure and Clasius-Clapeyron Equation:
5.
The vapor pressure of liquid A increases by a factor of 2 when its temperature is increased from 300
K to 320 K. The vapor pressure of liquid B increases by a factor 1.5 when its temperature is increased
from 300 K to 320 K. (a) Is the heat of vaporization of A higher or lower than that of B? Explain. (b)
Which liquid has the higher boiling point, liquid A or liquid B? Explain.
6.
The boiling point of iso-octane, C8H18, is 99.2oC and its enthalpy of vaporization, Hvap = 35.76
kJ/mol. Estimate the vapor pressure of iso-octane at 25oC. (Assume that its enthalpy of vaporization
stays constant.)
7.
Hexane, C6H14, has enthaply of vaporization, Hvap = 30.1 kJ/mol, and at 25oC, its vapor pressure is
148 mmHg. Estimate the boiling point of hexane.
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Chem 1A
Chapter 10 Exercises
Exercises #3:
Crystal Structure – Atomic solids
1.
Platinum crystallizes into a cubic lattice structure that has a total of four Pt atoms per unit cell. (a)
What type of unit cell does platinum form? (b) What is the mass of a unit cell of platinum? (c) If the
density of platinum is 21.45 g/cm3, what are the edge length of the unit cell and the atomic radius of
platinum, respectively? (Express the edge length and atomic radius in picometers.)
(1 u = 1.6605 x 10-24 g; 1 pm = 10-10 cm)
(Answer: (a) face-centered cubic closest-pack; (b) 780.4 u or 1.296 x 10-21 g; (c) 392.4 pm; 138.7 pm)
2.
Iron forms a crystal lattice with body-centered cubic unit cell. If the atomic radius of iron is 126 pm,
what is the edge length of the unit cell? If the mass of iron atom is 55.847 u, calculate the density of
iron. (1 u = 1.6605 x 10-24 g)
(Answer: S = 291 pm; density = 7.53 g/cm3)
3.
Gold forms a face-centered cubic unit cell lattice and has a density of 19.32 g/cm3. Calculate the
atomic radius of gold. (Atomic mass of gold = 197.0 u) (Answer: 144.1 pm)
4.
Calcium has an atomic radius of 197 pm and the density is 1.55 g/cm3. (a) Which type of cubic
structure does calcium form? (b) What is the edge length of the unit cell?
(Answer: (a) face-centered cubic; (b) 557 pm)
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Chem 1A
Chapter 10 Exercises
Crystal Structure – Ionic solids
5.
Calcium fluoride forms a crystal structure known as calcium fluorite structure, in which the Ca2+ ions
occupy the face-centered cubic lattice points. If the formula of calcium fluoride is CaF2, how many
Ca2+ and F- ions, respectively, are present in a unit cell of CaF2?
6.
Sodium chloride forms the “rock salt” structure, in which the larger Cl- ions occupy the face-centered
lattice points and the Na+ ions fill up the octahedral holes at the center and the middle of edges of the
cube. (a) How many Na+ ions and Cl- ions, respectively, are present in one unit cell of NaCl? (b)
What are the masses of a unit cell of NaCl in amu and in grams, respectively? (c) How many unit
cells are present in 1.00 mole of NaCl? (c) If the ionic radii of Na+ and Cl- are 95 pm and 181 pm,
respectively, calculate the volume of a unit cell in pm3 (cubic picometers) and in cm3 (cubic
centimeters). (d) What is the density of NaCl in g/cm3? [Note: oppositely charged ions along the
edges are touching, but identical ions along the diagonal faces are not. Atomic masses of Na and Cl
are 22.99 u and 35.45 u; 1 u = 1.6605 x 10-24 g; 1 pm = 10-10 cm]
7.
Cesium chloride forms a cubic crystal in which the Cl- ions occupy the simple cubic lattice points and
Cs+ ion occupies the cubic hole at the center of the unit cell. (a) Calculate the mass of a unit cell of
CsCl. (b) If the ionic radii of K+ and Cl- are 167 pm and 181 pm, respectively, what is the edge length
(in pm) of the cubic unit cell of CsCl. (c) Calculate the density of CsCl (in g/cm3)?
(Assume oppositely charged ions along the body diagonal are touching, but identical ions along the
edge are not. Atomic masses of Cs and Cl are 132.9 u and 35.45 u; 1 u = 1.6605 x 10-24 g]
8.
Zinc sulfide (or zinc blend) forms a face-centered cubic crystal with the sulfide ions occupy the
corner and face-center lattice points and zinc ions fill up the “tetrahedral holes” within the unit cell
formed by the sulfide ions. (a) What is the formula of zinc sulfide? (b) What is the total number of
ions (Zn2+ plus S2-) are present in a zinc blend unit cell? (c) Calculate the mass of the unit cell in amu
and in grams, respectively. (d) How many unit cells are present in 1.00 mole of zinc sulfide?
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