Name:
First Midterm
General Chemistry II 1152
February 14, 2003
( )= ( − )
ln ( ) = ( − )
L ⋅atm
J
R = 0.08206 mol
⋅ K = 8.314 mol ⋅ K
ln
1
1
[ A] − [ A]0 = kt
P2
P1
k1
k2
∆Hvap 1
1
T1
R
T2
Ea 1
1
R T1
T2
1. Which should have the largest dipole moment?
a. H2(g)
b. CO2(g)
c. KCl(g)
d. CH3F(g)
2. Which of the following molecules does not have a dipole moment?
a. CH2=CH2
b. NH3
c. CH3NH2
d. HCl
3. Which has the smallest dipole-dipole forces?
a. CH3F
b. HCl
c. N2
d. CO
4. Which is expected to have the largest dispersion forces?
a. C2H6
b. C8H18
c. N2
d. CO2
5. Which covalent bond is the most polar?
a. N-F
b. C-F
c. Cl-F
d. F-F
6. Which of the following compounds exhibits hydrogen bonding?
a. CH3Cl
b. HI
c. H3C-O-CH3
d. NH3
1 - GenChem 1152 1st midterm
 [ A] 
ln [ A]0  = kt
7. How much heat is released when 75.0 g of steam at 100.0°C is cooled to ice at -15.0°C? The
enthalpy of vaporization of water is 40.67 kJ/mol, the enthalpy of fusion for water is 6.01 kJ/mol,
the molar heat capacity of liquid water is 75.4 J/(mol•°C), and the molar heat capacity of ice is
36.4 J/(mol•°C).
40.67 kJ/mol × 4.16 mol = 1 6 9kJ
J × 4.16 mol ×100.0°C × 1 k J = 31.4 kJ
75.4 mol⋅°C
1000 J
6.01 kJ/mol × 4.16 mol = 25.0 kJ
1kJ
J
36.4 mol⋅°C
× 4.16 mol ×15.0°C × 1000 J = 2.27 kJ
169 kJ + 3 1 . 4kJ + 2 5 . 0kJ + 2 . 2 7kJ = 228 kJ
8. A kitchen pressure cooker operates at 1.50 atm. The ∆Hvap of water is 40.7 kJ/mol. What is
the boiling point of water in the pressure cooker?
( )
( − )
ln( )
=( − )
−
P
ln P1 = −
2
P1
P2
∆Hvap
R
( )+
∆Hvap 1
R
T1
1
T1
P
ln P1
2
∆H
− Rvap
T1 = 385K
1
T2 =
1
T2
1
T2
(
ln 1.5atm
1atm
)
J
40700 mol
−
J
8.314 mol⋅K
1 = 1 = 0.00260
+ 373K
T1
or 112°C
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9. Classify by the kinds solids formed as molecular, covalent network, ionic, or metallic.
a. C8H18
b. Ag
c. RbI
molecular
metallic
ionic
d. SiO2
covalent network
10. A binary ionic compound, MxAy, crystallizes in a cubic structure that contains eight anions
(A) entirely within its unit cell and a cation (M) on each corner and on each face. What is the
empirical formula of this compound?
A = 8atoms
(
) (
)
M = 18 × 8corners + 12 × 6 faces = 4atoms
M 4 A8 → MA2
11. At a given temperature the vapor pressure of benzene and toluene are 183 mm Hg and 59.2
mm Hg, respectively. Calculate the total vapor pressure over a solution of benzene and toluene
with Xbenzene = 0.600.
° + X P°
Psoln = Xben Pben
tol tol
Psoln = (0.600 )(183mm) + ( 0.400 )( 59.2mm)
Psoln = 110mm + 23.7mm = 134mm
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12. An aqueous solution has a normal boiling point of 102.0°C. What is the freezing point of this
solution? For water Kb = 0.51° C/m and Kf =1.86° C/m.
∆t bp = k bp m
∆tbp
2.0°C
m=
=
= 3.9m
kbp
0.51 °C
m
(
)
∆t fp = k fp m = 1.86 °C
m ( 3.9m) = 7.3°C
freezing pt. = −7.3°C
13. A solution of 62.4 g of insulin in enough water to make 1.000 L of solution has an osmotic
pressure of 0.305 atm at 25.0° C. Based on these data, what is the molar mass of insulin?
= MRT
M=
RT
=
(
0.305atm
= 0.0125M
L⋅atm ( 298K )
0.08206 mol⋅K
)
g
62.4g
g
molar mass = mol = 0.0125M 1.000 L = 5.00 × 103 mol
(
)(
)
14. List the four factors that effect reaction rates.
a.
TEMPERATURE
b.
CONCENTRATION
c.
STATE OF SUBDIVISION
d.
PRESENCE OF A CATALYST
4 - GenChem 1152 1st midterm
15. The isomerization reaction, CH3NC → CH3CN, is first order and the rate constant is 0.46 s
–1
at 600 K. (a) What is the concentration of CH3NC after 0.20 min of reaction if the initial
concentration is 0.10 M? (b) What is the half-life of the reaction?
a.
 [A ] 
ln  [ A]  = −kt
 0
ln [ A] − ln[ A ]0 = −kt
ln[ A] = ln[ A ]0 − kt
(
)(
ln[ A] = ln (0.10 ) − 0.46s −1 0.20min× 60sec
min
)
ln[ A] = −2.303 − 5.5 = −7.8
[ A ] = e −7.80 = 4.1× 10 −4
b.
kt 1 = 0.693
2
0.693 = 1.5 s
t 1 = 0.693
−1
k =
2
0.46 s
16. The following set of data was obtained by the method of initial rates for the reaction:
2–
2 HgCl2 (aq) + C2O4
–
(aq) → 2 Cl (aq) + Hg2Cl2 (s) + 2 CO2 (g)
The following initial rates of reaction have been observed for certain reactant concentrations:
[HgCl2], mol L
-1
2–
[C2O4 ], mol L
-1
Rate, mol, L
0.10
0.10
1.3 x 10
0.10
0.20
5.2 x 10
0.20
0.20
1.0 x 10
-1 -1
h
–7
–7
–6
2–
What is the rate equation for the describing the rate dependence on the concentration of C2O4
and HgCl2? (5 pt)
[
rate = k[ HgCl2 ] C2O4 2−
]
2
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What is the value of the rate constant? (4 pt)
k=
−7
−4
rate
= 1.3×10 2 = 1.3 × 10
2
2−
( 0.10) 0.10
[ HgCl2 ] C2O4
[
(
]
)
What is the order of the reaction in each reactant and the overall order of the reaction? (5 pt)
[
]
First order in [ HgCl2 ] , second order in C2O4 2− , third order overall.
17. The decomposition of dinitrogen pentoxide is described by the reaction below:
2 N2O5 (g) → 4 NO2(g) + O2(g)
If the rate of disappearance of N2O5 is equal to 1.40 mol/min, what is the rate of appearance of
NO2?
− 12
[
∆[ N2O5 ] 1 ∆ NO2
= 4 ∆t
∆t
]
∆ [ NO2 ]
∆[ N O ]
mol = 2.40 mol
= − 42 ∆t2 5 = 2 × 1.40 min
∆t
min
6 - GenChem 1152 1st midterm