HCCS
General Chemistry
1412 Exam 1
Fall 2010
Dr. Komala Krishnaswamy
10/6/2010
CHEM 1412 EXAM # 1 Fall 2010
Name:
Score:
Part I-Please DO NOT circle. Write the correct answer in space provided. (3 points each)
_____1. Calculate the molality of a solution prepared by dissolving 16 g of urea,
NH2CONH2, in 39 g of H2O.
A. 0.48 m
B. 0.68 m
C. 4.8 m
D. 0.0048 m
E. 6.8 m
_____2. Which of the following will be most soluble in H2O?
A. Ar
D. CH4
B. O2
E. KCl
C. CO2
_____3. Calculate the molarity of a solution prepared by dissolving 16 g of urea,
NH2CONH2, in 39 g of H2O. The density of the solution is 1.3 g/mL.
A. 0.068 M
D. 6.3 M
B. 3.7 M
E. 0.41 M
C. 4.8 M
_____4. Calculate the concentration of N2 in H2O at a partial pressure of 0.826 atm. The
Henry’s law constant for N2 in H2O is 6.8 × 10-4 M.atm-1
A. 5.6 × 10–4 M
D. 0.43 M
B. 1.2 × 103 M
E. 8.2 × 10-4 M
C. 8.2 × 10–3 M
_____5. The vapor pressure of pure ethanol at 60°C is 349 mm Hg. Calculate the vapor
pressure over a solution prepared by dissolving 10.0 mol naphthalene in
90.0 mol ethanol?
A. 34.9 mm Hg
D. 279 mm Hg
B. 314 mm Hg
E. 69.8 mm Hg
C. 600 mm Hg
_____6. The freezing point of ethanol, C2H5OH, is -114.6°C. Its molal freezing point
depression constant is 2.00 °C/m. What is the freezing point of a solution
prepared by dissolving 50.0g of glycerin, C3H8O3 in 200g of ethanol?
A. -115 °C
D. -120 °C
B. -5.4 °C
E. -109 °C
C. -132 °C
____7. Which of the following aqueous solutions has the lowest osmotic pressure?
A. 0.18 M KCl
D. 0.05 M K2CO3
B. 0.15 M Na2SO4
C. 0.12 M Ca(NO3)2
E. 0.10 M C2H6O2 (ethylene glycol)
_____8. For the reaction 4 NH3 + 7 O2 → 4 NO2 + 6H2O at a particular time,
–Δ[NH3]/Δt = 1.5 × 10–2 M/s. What is -Δ[O2]/Δt at the same instant?
A. 8.6 × 10-3 M/s
-2
D. 2.6 × 10 M/s
B. 2.3 × 10–2 M/s
E. 4.4 × 10-3 M/s
C. 1.5 × 10–2 M/s
_____9. The rate law of the reaction A B was found to be rate = k[A]2. If the
concentration of A is tripled what happens to the rate of the reaction?
A. Increases by a factor of 3
C. Increases by a factor of 9
E. Is unaffected
B. increases by a factor of 6
D. increases by a factor of 2
_____10. If the reaction 2A + 3B  products is 1st order in A & 2nd order in B, then the
rate law will have the form
A. Rate = k[A][B]
D. Rate = k[A]2[B]
B. Rate = k[A]2[B]3
E. Rate = k[A]2[B]2
C. Rate=k[A][B]2
_____11. The reaction 2NO2  2NO + O2 has the rate law, rate = k[NO2]2. Calculate the
value of the rate constant, k, if the [NO2] drops fro, 0.0100 M to 0.00650 M in
100s.
A. 0.096
D. 1.2
B. 0.65
E. 0.54
C. 0.81
_____12. A 2nd order reaction has a half-life of 18 s when the initial reactant
concentration is 0.71 M. Calculate the rate constant for the reaction.
A. 0.078 M-1s-1
D. 1.3 M-1s-1
B. 0.038 M-1s-1
E. 0.71 M-1s-1
C. 0.020 M-1s-1
_____13. Identify the intermediates in the following mechanism:
X + YO2  XO + YO
XO + YO  XO2 + YO
YO + O2  YO + O
YO + O  YO2
A. X only
D. O, XO & YO
B. YO2 only
E. YO2 & O2
C. X & YO2
_____14. The proper expression for Kc for the reaction below is
4CuO(s) + CH4(g)  CO2(g) + 4Cu(s) + 2H2O(g)
A. [CuO]/[Cu]
D. [CO2][H2O]2/[CH4]
B. [CuO]4/[Cu]4
C. [Cu]4/[CuO]4
2
E. [CH4]/[CO2][H2O]
_____15. Calculate the equilibrium constant, Kc, for the reaction below if a 3.25 L tank
was found to contain 0.343 mol O2, 0.0212 mol SO3 and 0.00419 mol SO2.
2SO3(g)  2SO2(g) + O2(g)
A. 6.78 × 10-2
D. 4.35 × 10-2
B. 1.34 × 10-2
E. 4.60 × 10-3
C. 4.12 × 10-3
_____16. Calculate the equilibrium constant Kp for the following equilibrium at 25 °C
given that the equilibrium constant, Kc = 3.0 × 105 at the same temperature.
2H2S(g) + 3O2(g)  2SO2(g) + 2H2O(g) Kc = 3.0 × 105
A. 1.2 × 104
D. 3.3 × 105
B. 8.2 × 10–5
E. 1.5 × 105
C. 3.3 × 10–6
_____17. If the equilibrium constant for reaction (1) is K, what is the equilibrium
constant for reaction (2)?
(1)
(2)
A. K3
D. 3/K
(1/3)N2(g) + H2(g)  (2/3)NH3(g)
2NH3(g)  N2(g) + 3H2(g)
B. 3K
E. 1/K3
C. 1/3K
____18. The equilibrium constant, Kc, for the equilibrium 2CO2(g)  2CO(g) + O2(g)
is 1.2 × 10-13. If the instantaneous concentrations are [CO] = 0.0127 M,
[CO2] = 0.0l89 M, [O2] = 0.00402 M, which of the following statements is true?
A. The reaction mixture is at equilibrium
B. The system is not at equilibrium; more CO2 will form
C. The system is not at equilibrium; [CO2] will decrease
D. The system is not at equilibrium; [CO] will increase
E. The system is not at equilibrium; PO2 will increase
_____19. The equilibrium constant, Kc, for the reaction 2HI(g)  H2(g) + I2(g) is
0.016. Calculate the equilibrium value of [I2] if the equilibrium [H2] = [HI] =
0.10 M.
A. 0.013 M
D. 1.3 M
B. 0.040 M
E. 0.016 M
C. 0.31 M
_____20.Consider the following equilibrium:
N2(g) + 3H2(g) 2NH3(g)
H°=- 92.4 kJ
Which of the following disturbances will increase the concentration of NH3 in
the mixture?
A. Increasing the temperature
B. Removing NH3 from the mixture
C. Increasing the container volume
D. Decreasing the partial pressure of N2
E. All of the above
PART II- ( 8 points each) Please show all your work .
21. The osmotic pressure of a 12 mL aqueous solution containing 0.60 g of dissolved
nicotine is 7.55 atm at 25 °C. Calculate the molar mass of nicotine.
(R = 0.0821 L.atm.K-1.mol-1)
22. a. Calculate the rate constant of a first order reaction A B if the initial concentration
of A is 0.373 M and the concentration of A after 122 s is 0.0974 M.
b. Calculate the half-life of the reaction.
-3 -1
23. Calculate the activation energy of a reaction that has a rate constant of 4.41 × 10 s
at 42 °C and a rate constant of 9.79 × 10-2 s-1 78°C. (R=8.314 JK-1mol-1)
24. 0.64 moles of NOBr were placed in a 1.00 L reaction chamber. After equilibrium was
reached, 0.46 moles of NOBr remained. Calculate the equilibrium constant, Kc, for
the reaction 2NOBr(g) 2NO(g) + Br2(g).
25. Kc for the reaction 2AB(g) A2(g) + B2(g) is 16. If 0.030 mol of AB(g) is
introduced into a 1.00 L vessel, calculate the equilibrium concentrations of AB(g),
A2(g) and B2(g).
Bonus (10 points). The following rate data was collected for a reaction
2A + B  products
Exp
1
2
3
A.
B.
C.
D.
[A]
0.030 M
0.060 M
0.060 M
[B]
0.044 M
0.044 M
0.066 M
-[A]/t (M/s)
0.500
0.500
1.125
Determine the Rate law
Calculate the rate constant; include units.
What will be the rate of consumption of A when [A] = [B] = 0.10 M?
What will be the rate of consumption of B under the same conditions?
Exam 1 Fall 2010 Chem 1412 Key
1.E
9. C
17. E
2.E
10. C
18. B
3. D
4. A
11. E
12. A
19. 0.0016 20. B
5. B
13. D
6. D
14. D
7. E
15. C
8. D
16. A
21.
7.55
mol/L  0.309 mol/L; moles of solute  0.309  0.012 mol  0.0037 mol
0.0821  298
0.60 g
Molar mass 
 160 g.mol 1
0.0037 mol
  7.55atm; M 
22.
a.
k
ln A0  ln At ln 0.373  ln 0.0974

 0.0110 s -1
t
122 s
b.
t 1/2 
0.693
s  63.0 s
0.0110
23.
k
R  ln  1
 k2
Ea 
1
1

T2 T1
24.
I
C
E

 8.314  ln  0.0979 

 0.00441  J/mol  7.92  10 4 J/mol
1
1

315 351
2NOBr
0.64
0.46-0.64 = -0.18
0.46
2NO
0
+ 0.18
0.18
Br2
0
+0.18/2 = 0.090
0.090
2

Br2 NO
Kc 
NOBr2

0.090  0.18 2
 0.014
0.46 2
25.
2AB
0.030
-x
0.030-x
I
C
E
x

B 2 A 2 
4
Kc 
;16 
;
2
0.030 - x 2
AB
A2
0
+ x/2
x/2
2
16  4 
B2
0
+x/2
x/2
x
2
0.030 - x 
x
; 80.030 - x   x; 0.24 - 8x  x; 0.24  9x; x  0.24/9  0.027 M
0.030  x
x 0.027
[A 2 ]  [B 2 ]  
M  0.013M; [AB]  0.030 - x  0.030 - 0.027  0.003 M
2
2
8
Bonus (10 points).
A.
0.500
0.060 x
1
 2 x ; x  0  order with respect to A
0.500
0.030 x
1.125
0.066 y
 2.25 
 1.5 y ; y  ln(2.25)/l n(1.5)  2  order with respect to B
y
0.500
0.044
2
 rate  k[B]
B. k 
rate
B
2

0.500
0.044
2
M 1s 1  258M 1s 1
C. rate of consumptio n of A  258  0.1 Ms -1  2.58 Ms -1
2
D. rate of consumptio n of B 
rate of consumptio n of A  2.58
Ms -1  1.29 Ms -1
2
2