CHM2045: Fall 2010
Exam #4
December 1, 2010
FORM B
Instructions: BEFORE YOU BEGIN, MARK YOUR NAME, USF ID NUMBER, SECTION
NUMBER, AND FORM LETTER ON YOUR SCANTRON SHEET. FAILURE TO DO THIS WILL
RESULT IN A PENALTY.
Coulomb’s law: F  8.988  10 9 ( Nm 2 / C 2 ) q1q 2 2 
r 

R = 0.08206 atm L mol–1 K–1
= 8.314 J mol–1 K–1
1 Ǻ = 10–8 cm
CHM2045: Fall 2010
Exam #4 FORM B
December 1, 2010
For each problem determine the best answer and mark the appropriate place on your scantron sheet. The
exam consists of 27 questions to earn up to 25 correct answers. You will be given 75 minutes.
1) For each molecule (or ion) indicate whether the dipole moment is equal to zero or not. Answer “Yes”
if the dipole moment is equal to zero and “No” if it is not equal to zero.
CN–; CH3Br; H2O; NO3–; NH3
a) No; No; No; Yes; No
b) No; Yes; No; No; Yes
c) Yes; No; Yes; No; Yes
d) Yes; No; No; Yes; No
e) Yes; Yes; Yes; Yes; No
2) Compared to a substance with weak intermolecular attractions, a substance with strong intermolecular
attractions generally has...
a) a higher normal boiling point and vapor pressure, but a lower heat of vaporization
b) a lower normal boiling point, but higher vapor pressure and heat of vaporization
c) higher heat of vaporization but lower normal boiling point and vapor pressure
d) a lower normal boiling point and heat of vaporization, but higher vapor pressure
e) lower vapor pressure, but higher normal boiling point and heat of vaporization
3) Identify the molecule with the highest boiling point and the correct explanation for why the boiling
point is highest.
CH3CH2CH2NH2; CH3OCH2CH3; CH3CH2CH2CH3; N(CH3)3; CH3CH2CH2F
a) CH3CH2CH2NH2 ; only one with H- bonding
b) CH3OCH2CH3 ; one of many with H-bonding
c) CH3CH2CH2CH3 ; ion-ion bond is higher than others
d) CH3CH2CH2F ; higher lattice energy than others
e) Equal boiling points ; they all have the same molecular weight
4) What is the enthalpy change when 100 g of water at 50 °C turns into ice at –30 °C?
Specific heat values: ice = 2.09 J/g K; water = 4.18 J/g K; steam = 1.84 J/g K;
water ΔH fusion = 6.01 kJ/mol and ΔH vaporization = 40.67 kJ/mol
a) 60.6 kJ
b) –60.6 kJ
c) –20.9 kJ
d) –27 kJ
e) –39.7 kJ
5) 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
6) Which of the following statements about change of state is FALSE?
a) The boiling point of a liquid depends on the gas pressure above the liquid.
b) Condensation is an endothermic process.
c) Evaporation occurs at the surface of a liquid, but boiling may occur at any point within the liquid.
d) Energy is absorbed by a liquid as it boils.
e) A liquid boils when its vapor pressure is slightly greater than the pressure above it.
7) Which of the following bonds is hardest to break?
a) the H–O bond in water
b) the hydrogen bond between 2 water molecules
c) the H–F bond in hydrogen fluoride
d) the H–C bond in methane
e) the H–N bond in ammonia
8) What is the number of lone pair on the Cl atom and the molecular geometry of the chlorite ion ClO2–?
a) 0 and linear
b) 1 and linear
c) 2 and linear
d) 1 and bent
e) 2 and bent
9) Based on the following information, which compound has the strongest intermolecular forces?
Substance
ΔHvap (kJ/mol)
Argon (Ar)
6.3
Benzene ( C6 H6 )
31.0
Ethanol ( C2H5OH )
39.3
Water ( H 2 O )
40.8
Methane ( CH 4 )
9.2
a) Argon
b) Benzene
c) Ethanol
d) Water
e) Methane
10) The shape of the meniscus of a liquid is determined by __________.
a) the viscosity of the liquid
b) the type of container material only
c) the relative magnitudes of cohesive forces in the liquid and adhesive forces between the liquid
and its container
d) the amount of hydrogen bonding in the liquid
e) the volume of the liquid
11) Diethyl ether is a volatile organic compound. The vapor pressure of diethyl ether is 401 mm Hg at 18
°C and the ΔHvap = 26.0 kJ/mol. Calculate the vapor pressure of diethyl ether at 25 °C.
a) 401 mm Hg
b) 500 mm Hg
c) 517 mm Hg
d) 598 mm Hg
e) 605 mm Hg
12) The critical point in a phase diagram represents
a) A set of temperature and pressure at which the substance is in equilibrium between two states on
either side of the line
b) The unique set of conditions at which three states are equally stable and in equilibrium
c) A representation of changes in temperature and pressure
d) The map of the state or phase of a substance as a function of pressure
e) The temperature and pressure above which a supercritical fluid exists
13) The geometric arrangement of ions in crystals of LiF is the same as that in NaCl. The unit cell of LiF
is 4.02 Ǻ on an edge. Calculate the density of LiF from the size of the unit cell.
Li = 6.94 amu, F = 19 amu
a) 0.65 g/cm3
b) 6.55 g/cm3
c) 1.98 g/cm3
d) 2.65 g/cm3
e) 3.2 g/cm3
14) Which molecule has the largest H–M–H bond angle (M = C, N, or O)?
a) CH4
b) NH3
c) H2O
d) NH4+
e) O=CH2
15) In the following phase diagram (P vs. T). Which set of labels is correctly identified?
a) A-solid, B-gas, D-solid + liquid
b) B-liquid, G-liquid+gas, E-liquid+solid+ gas
c) D-liquid+solid, F-liquid+gas, H-liquid
d) B-gas, C- lilquid, F liquid+gas
e) E-liquid-solid, D- gas-solid, F-liquid-gas
16) The standard heat of formation of CaBr2 is –675 kJ/mol. The first ionization energy of Ca is 590
kJ/mol and its second ionization energy is 1145 kJ/mol. The heat of sublimation [Ca(s)  Ca(g)] is
178 kJ/mol. The bond energy of Br2 is 193 kJ/mol, the heat of vaporization [Br2(l)  Br2 (g)] is 31
kJ/mol and the electron affinity of Br is –325 kJ/mol. Calculate the lattice energy of CaBr2.
a) –1137 kJ/mol
b) –812 kJ/mol
c) –2487 kJ/mol
d) –2162 kJ/mol
e) –2112 kJ/mol
17) Which molecule/ion is polar?
a) AlCl3
b) NH4+
c) SO42–
d) BrF3
e) XeF4
18) Which of the following reactions is associated with the lattice energy of CaS (ΔH°latt)?
a) Ca2+(g) + S2–(g) → CaS(s)
b) Ca2+(aq) + S2–(aq) → CaS(s)
c) CaS(s) → Ca2+(aq) + S2–(aq)
d) Ca(s) + S(s) → CaS(s)
e) CaS(s) → Ca(s) + S(s)
19) How much energy is required to vaporize 98.6 g of ethanol (C2H5OH) at its boiling point, if its ΔHvap
is 40.5 kJ/mol?
a) 52.8 kJ
b) 39.9 kJ
c) 18.9 kJ
d) 86.7 kJ
e) 11.5 kJ
20) Choose the best Lewis structure for XeI2.
a)
b)
c)
d)
e)
21) Which molecule or compound below contains a polar covalent bond?
a) ZnS
b) NCl3
c) AgCl
d) F2
e) C2H4
22) What is the molecular geometry of IF4–?
a) square planar
b) tetrahedral
c) square pyramidal
d) seesaw
e) trigonal bipyramidal
23) Determine the electron geometry (EG) and molecular geometry (MG) of XeF2.
a) EG = tetrahedral, MG = linear
b) EG = trigonal bipyramidal, MG = bent
c) EG = trigonal bipyramidal, MG=linear
d) EG=linear, MG=linear
e) EG=tetrahedral, MG=bent
24) Arrange these compounds (KBr, RbBr, CaBr2, MgO) in order of increasing lattice energy.
a) RbBr < KBr < MgO < CaBr2
b) KBr < RbBr < MgO < CaBr2
c) RbBr < CaBr2 < MgO < KBr
d) RbBr < KBr < CaBr2 < MgO
e) KBr < RbBr < CaBr2 < MgO
25) Which of the following compounds does not exhibit hydrogen bonding?
a) CH4
b) NH4
c) H2O
d) HF
e) All of them exhibit H-bonding.
26) Which of the atoms below is least likely to form an expanded octet in a correctly drawn Lewis
structure?
a) P
b) S
c) I
d) Cl
e) N
27) Put these molecules in order of increasing bond length: N2, O2, F2.
a) N2 > O2 > F2
b) N2 > F2 > O2
c) O2 > F2> N2
d) F2 > O2 > N2
e) F2 > N2 > O2
Mark your name, U-ID, Section #, and Form B on your scantron!