Chapter 12 Study Questions

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Honors Chemistry
Chapter 10 Study Questions
1. Using the Equilibrium Vapor Pressure of Water Table (see next page):
a) Find the equilibrium vapor pressure of water at 15C.
b) The boiling point of water in a pressure cooker is 117C; what is the air pressure over the
water?
c) On a certain day, the relative humidity is 100% and the temperature is 5C. What is the
vapor pressure of water on that day? What is the relative humidity later that day when the
temperature rises to 18C (assuming the water vapor pressure doesn't change)?
d) What is the vapor pressure of water in the air on a day when the relative humidity is
80.0% and the temperature is 22C?
e) What is the dew point in (d)?
2. For each of the following pairs of substances, specify the type of interparticle bonding in each,
and indicate which one has the higher boiling point:
a) NH3 or PH3
b) C4H10 or C6H14 c) CO2 or H2O d) HCl or LiCl e) Na or NaCl
3. For each of the following types of solids, describe its structure and the nature of the forces
holding it together, and give the formula of at least one example: (a) ionic; (b) covalent
(molecular); (c) metallic; (d) network covalent
4. List the substance types in (3) in order of increasing melting point.
5. Which of the types of substances in (3) conduct electricity as solids? as liquids?
6. Of the following substances: NaCl, diamond, Fe, F2, C3H7OH, which one
a) has the lowest boiling point?
b) is held together by ionic bonds?
7. Define boiling point, critical temperature, critical pressure, and triple point.
8. Explain how each of the following affects the vapor pressure of a liquid: (a) surface area; (b)
temperature; (c) intermolecular attractive forces; and (d) volume of liquid.
9. What are the three types of intermolecular attractive forces and list them in order of increasing
strength?
10. The normal (1 atm) melting and boiling points of O2 are -218C and -183C, respectively.
Its triple point is at -219C and 1.14 x 10-3 atm, and its critical point is at -119C and 49.8
atm. (a) Sketch the phase diagram for O2, showing the 4 points given above and indicating
the area in which each phase is stable. (b) Which is denser, O2(s) or O2(l)? Explain. (c) As
it is heated, will solid O2 sublime or melt at a pressure of 1 atm?
11. The vapor pressure of solid iodine (I2) at 30°C is 0.466 mm Hg. How many milligrams of
iodine will sublime into an evacuated 1.00-liter flask?
Summary of Chapter 10: Liquids and Solids
Differences between gas, liquid, solid
sublimation
Relationship of interparticle forces and Hfus, Hvap, melting pt and boiling pt
vapor pressure
equilibrium vapor pressure of water as f(T)
relative humidity
dew point
boiling point
heating curve
critical temperature & pressure
phase diagrams
triple point
Intermolecular forces:
London dispersion forces, dipole forces, hydrogen bonds
Properties of the following types of solids (conductivity, melting points, solubility):
molecular, network covalent, ionic, metallic
Honors Chemistry
Answers to Chapter 10 Study Questions
1. a) 12.8 mm Hg
b) (1310 mm Hg + 1397 mm Hg)/2 = 1354 mm Hg
c) 6.5 mm Hg; % RH = vapor pressure
x 100% = 6.5 mm Hg = 42%
equil. vapor p. at 18C
15.5 mm Hg
d) % RH =
v.p.
e.v.p. at 22C
x 100%; 80% =
x
19.8 mm Hg
x 100%; x = 15.8 mm Hg
e) 100% = 15.8 mm Hg x 100%; x = 15.8 mm Hg  18.3C
x
2. a) NH3 (H-bonds)/PH3 (dipole); NH3
b) both LDF; C6H14 (higher molar mass)
c) CO2 (LDF)/H2O (H-bonds; H2O) (also, H2O is a liquid, while CO2 is a gas)
d) HCl (dipole)/LiCl (ionic); LiCl
e) Na (metallic)/NaCl (ionic); NaCl
3. a) Ionic solids are composed of positive and negative ions arranged so that each positive ion
is surrounded by negative ions and vice versa. The are held together by the attractive force
between the oppositely charged ions. Some examples are NaCl, NaNO3, MgSO4, CuCl2.
b) Covalent (molecular) solids are made up of molecules. Covalent bonds hold together the
atoms within the molecules. The forces between the molecules are dispersion and dipole
forces and hydrogen bonds. Examples include water (H2O), ammonia (NH3), table sugar
(C12H22O11), CO2.
c) Metallic solids are made up of a regular crystalline array of metal atoms. Valence
electrons are free to move within the solid and make up the "metallic bonding" that holds the
metal together. Some metallic solids are aluminum, gold, iron, nickel, copper, zinc, sodium.
d) Network covalent solids consist of atoms covalently bound together in a continuous 3dimensional network. The solid is held together by covalent bonds. Examples are diamond
(C), carborundum (SiC) and quartz (SiO2).
4. In general, b) molecular < c) metallic < a) ionic < d) covalent network
5. Only metallic substances conduct electricity as solids. Both metallic and ionic substances
conduct electricity as liquids.
6. a) F2 (molecular, LDF)
b) NaCl
7. The boiling point of a liquid is the temperature at which its equilibrium vapor pressure is
equal to external pressure. The critical temperature is the highest temperature a substance
can be liquified; above the critical temperature a substance is a gas at any pressure. The
critical pressure is the pressure needed to liquify a substance at its critical temperature. The
triple point is the temperature and pressure at which solid, liquid and gas all exist in
equilibrium.
8. a) no change; b) vapor pressure increases with increasing temperature; c) higher
intermolecular forces mean lower vapor pressure; d) no change.
9. London dispersion forces (van der Waals forces) < dipole-dipole forces < hydrogen bonds.
10. (a)
b) O2(s) is denser than O2(l) because the solid-liquid line on the phase diagram is normal
(slants slightly to the right).
c) O2 will melt when heated at a pressure of 1 atm.
11. First find the number of moles of iodine in the flask, using the ideal gas law:
P = 0.466 mmHg = 6.13 x 104 atm; T = 30°C = 303 K; V = 1.00 L; n = ?
n


6.13 x 10 4 atm 1.00 L 
PV

 2.46 x 10-5 moles
0.0821303 K 
RT
2.46 x 10-5 moles x
253.8 g I 2 1000 mg
= 6.25 mg
x
1 mole I 2
1g
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