Download Multiple-choice Questions 1-26

CHEM 218 Final Exam 2A
Multiple-choice Questions 1-26
Circle the appropriate response.
(2 marks each)
1. How many hydrogen bonds are formed between G and A?
a)
b)
c)
d)
e)
0
2
1
3
4
2. What is the equilibrium constant expression for the reaction below?
CaO(s) + CO2(g) ↔ CaCO3(s)
a)
b)
c)
d)
e)
Kc = [CO2]
Kc = [CaCO3]/[CaO]
Kc = [CaCO3]/[CaO][CO2]
Kc = 1/[CO2]
Kc = [CaO][CO2]/[CaCO3]
3. The pH of a 0.050 M aqueous solution of calcium hydroxide is
a)
b)
c)
d)
e)
13.00
12.70
12.40
12.00
1.00
4. Which one of the following salts gives a basic aqueous solution?
a)
b)
c)
d)
e)
NaHS
NaHSO4
NiCl2
NH4ClO4
(CH3)NH3Cl
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CHEM 218 Final Exam 2A
5.
Calculate the work needed to make room for products in the combustion of 1 mole of
CH4(g) to carbon dioxide and water vapor at STP (1 L · atm = 101 J).
a)
b)
c)
d)
e)
–4.52 kJ
–2.26 kJ
–6.79 kJ
–11.3 kJ
no work is needed
6.The standard potential of the cell
In(s)⏐In3+(aq)⏐Cu2+(aq)⏐Cu(s)
is +0.68 V at 25oC. If the standard potential of the Cu2+/Cu couple is +0.34 V, calculate
the standard potential of the In3+/In couple.
a)
b)
c)
d)
e)
+0.34 V
–0.34 V
–0.23 V
+1.02 V
–0.68 V
7. Which of the following is the strongest reducing agent?
a)
b)
c)
d)
e)
Fe2+
H2
Co2+
F–
Cr2+
7. The standard potential of the Ag+/Ag electrode is +0.80 V and the standard potential of
the cell
Fe(s)⏐Fe3+(aq)⏐Ag+(aq)⏐Ag(s)
is +0.84 V. What is the standard potential of the Fe3+/Fe electrode?
a)
b)
c)
d)
e)
+0.04 V
+1.64 V
–1.64 V
–0.04 V
–0.12 V
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CHEM 218 Final Exam 2A
8. The standard potential of the cell
Tl(s)⏐Tl+(aq)⏐Cl–(aq)⏐AgCl(s)⏐Ag(s)
is +0.56 V at 25oC. If the standard potential of Tl+ is –0.34 V, calculate the standard
potential of the AgCl/Ag,Cl– couple.
a)
b)
c)
d)
e)
–0.22 V
+0.22 V
–0.90 V
–0.56 V
+0.90 V
10. For the reaction: C2H6(g) → 2CH3(g)
rate = k[C2H6]
If k = 5.50 × 10–4 s–1 and [C2H6]initial = 0.0200 M, calculate the rate of reaction after 1
hour.
a)
b)
c)
d)
e)
The rate of reaction is zero since the reaction is complete.
1.52 × 10–6 M·s–1
5.50 × 10–4 M·s–1
2.76 × 10–3 M·s–1
1.10 × 10–5 M·s–1
11. An elementary process has an activation energy of 32 kJ/mol. If the activation energy for
the reverse reaction is 20 kJ/mol, what is the enthalpy change for the reaction?
a)
b)
c)
d)
e)
–52 kJ/mol
–12 kJ/mol
–20 kJ/mol
52 kJ/mol
12 kJ/mol
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CHEM 218 Final Exam 2A
12. Given: 4PH3(g) → P4(g) + 6H2(g)
rate = k[PH3]
If the rate constant is 0.0278 s–1, calculate the percent of the original PH3 which has
reacted after 76.0 s.
a)
b)
c)
d)
e)
87.9%
12.1%
47.3%
97.9%
2.10%
13. The rate law for the mechanism below is
Cl2(g) ↔ 2Cl(g)
Cl(g) + CO(g) ↔ COCl(g)
COCl(g) + Cl2(g) → COCl2(g) + Cl(g)
a)
b)
c)
d)
e)
K1, fast
K2, fast
k3, slow
rate = k3[COCl][Cl2]
rate = k3 K1 K2[CO][Cl2]
rate = k3[COCl][Cl2]1.5
rate = k3 K1 0.5 K2[CO][Cl2]1.5
rate = k3 K1 0.5 K2[CO][Cl2]0.5
14.The rate of formation of oxygen in the reaction
2N2O5(g) → 4NO2(g) + O2(g)
is 2.28 (mol O2)·L–1·s–1. What is the rate at which N2O5 is used?
a)
b)
c)
d)
e)
–9.12 (mol N2O5)·L–1·s–1
–1.14 (mol N2O5)·L–1·s–1
–4.56 (mol N2O5)·L–1·s–1
–0.57 (mol N2O5)·L–1·s–1
–2.28 (mol N2O5)·L–1·s–1
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CHEM 218 Final Exam 2A
15. What is the approximate shape around each boron atom in diborane?
a)
b)
c)
d)
e)
tetrahedral
square planar
trigonal bipyramidal
see-saw
angular
16. Crude silicon is prepared by
a)
b)
c)
d)
e)
the reaction of SiO2(g) with Cl2(g).
the reduction of SiO2(s) with high–purity carbon.
the reaction of SiO2(s) with sodium hydroxide.
zone refining.
the reaction of SiCl4(l) with high–purity carbon.
17. Group 14 consists of the elements C, Si, Ge, Sn, and Pb. Which elements are metals?
a)
b)
c)
d)
e)
Sn and Pb
Ge, Sn, and Pb
Ge and Pb
Si and Ge
Pb
18. Which of the following is likely to form a saline hydride?
a)
b)
c)
d)
e)
Sr
Ti
W
P
As
19. Salts of sulfuric and sulfurous acid, respectively, are called
a)
b)
c)
d)
e)
sulfates and persulfates.
sulfates and sulfites.
sulfites and persulfates.
sulfates and persulfites.
sulfates and thiosulfites.
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CHEM 218 Final Exam 2A
20. Which of the Group 18 elements has the largest enthalpy of vaporization?
a)
b)
c)
d)
e)
Xe
Kr
Ar
Ne
He
21. What is the oxidation number of Cl in HClO2?
a)
b)
c)
d)
e)
+4
+3
+5
+2
+1
22. Dinitrogen pentoxide is the anhydride of
a)
b)
c)
d)
e)
nitric acid.
nitrous acid.
hydrazoic acid.
hydrazine.
dinitrogen tetroxide.
23. What nuclide is formed when tritium undergoes β decay?
a) β–
b) β+
c) 1H+
d) 4He2+
e) 3He
24. What nuclide is formed when 226Ra (radium) undergoes α decay?
a)
b)
c)
d)
e)
222Ra
222Rn
222Po
222At
218Po
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CHEM 218 Final Exam 2A
25. Nuclides with Z greater than 83 disintegrate mainly by
a)
b)
c)
d)
e)
α particle emission.
positron emission.
proton emission.
β particle emission.
neutron emission.
26. A nuclide undergoes positron emission to form 22Ne. What is the nuclide?
a)
b)
c)
d)
e)
23Na
23Mg
22Na
18O
22F
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CHEM 218 Final Exam 2A
Short-answer Questions 27-32
(4 marks each)
27. Consider the following reaction:
NH4(NH2CO2)(s) ↔ 2NH3(g) + CO2(g)
When 0.200 moles of NH4(NH2CO2)(s) are placed in a 1.50-L flask and allowed to reach
equilibrium at 400 K, 33.0% of the solid remains. Calculate the values of Kc and Kp for
the reaction.
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CHEM 218 Final Exam 2A
28. An aqueous acid solution of the dichromate ion (Cr2O72-) and NO2–(aq) are mixed and
the solution changes color from orange to pale violet (Cr3+). Write a balanced net ionic
equation for this reaction.
29. The following data were obtained for the disappearance of A at 25oC:
[A], M
0.090
0.069
0.054
0.042
0.032
0.025
0.019
Time, s
0
5
10
15
20
25
30
What is the order of the reaction and the rate constant?
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CHEM 218 Final Exam 2A
30. In the thermite reaction with Fe2O3(s), how many moles of iron are produced from
1.00 kg of Fe2O3(s)?
31. The Lunar Lander used the following reaction for propulsion:
NH2N(CH3)2(l) + 2N2O4(l) → 3N2(g) + 2CO2(g) + 4H2O(g)
Calculate ΔGo and Keq for this reaction. Do your calculations give you confidence that
this reaction works? Explain. The standard free energies of formation of NH2N(CH3)2(l),
N2O4(l), CO2(g), and H2O(g) are +210 (estimated), +97.54, –394.36, and –228.57
kJ,mol–1, respectively.
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CHEM 218 Final Exam 2A
32. Calculate the binding energy per nucleon for boron-10.
[10B, 10.0129 u; 1H, 1.0078 u; n, 1.0087 u and 1 u = 1.6605 x 10-27 kg]
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CHEM 218 Final Exam 2A
Long-answer Questions 33-36
(6 marks each)
33. Consider the following equilibrium for the dimerization of nitrogen dioxide:
2NO2 (g) ↔ N2O4 (g)
a. Calculate the ΔGo of this reaction.
b. What is the Kp for this reaction at 25oC ?
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CHEM 218 Final Exam 2A
34. A voltage of 1.12 V at 25 oC was obtained from a galvanic cell using a Sn/Sn2+ electrode
and a Ag+/Ag electrode.
a. Write down the overall redox reaction.
b. Calculate Eocell under standard conditions (all ions in solution have 1.0 M
concentrations).
c. If [Ag+] = 0.35 M, what is the concentration of tin(II) ions?
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CHEM 218 Final Exam 2A
35. Draw the structural formula showing the geometry of THREE of the following.
a. nitrous oxide
b. white phosphorus
c. ozone
d. phosphorous acid
e. nitrate anion
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CHEM 218 Final Exam 2A
36. Given the following data and that the activation energy of the process is 84 kJ calculate
the rate constant for the reaction at 120 oC.
Temp. (oC)
k (s-1)
________________________________
25
6.47 x 10-13
60
2.33 x 10-11
100
6.16 x 10-10
________________________________
**** END OF EXAM ****
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CHEM 218 Final Exam 2A
Answer Key
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
a
d
a
a
e
b
e
d
b
b
e
a
d
c
a
b
a
a
b
a
b
a
e
b
a
c
Kc = [NH3]2[CO2]
= [2(0.67)(0.200)/(1.5)]2[(0.67)(0.200)/(1.5)]
= 2.85 x 10-3
Kp = (RT)ΔnKc
= [(0.0821)(400)]3[2.85 x 10-3]
= 101
28. Cr2O72- + 3NO2- + 8H+ →
2Cr3+ + 3NO3- + 4H2O
29. lnA
t
lnA vs t gives negative slope
-2.41
0
-2.67
5
-2.92
10
-3.17
15
-3.44
20
-3.69
25
-3.96
30
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CHEM 218 Final Exam 2A
First order
Rate constant = (-3.44 + 2.41)/20 = 0.05
30. Fe2O3 → 2Fe
Moles(Fe) = 2(1000 g)/(2(55.84 g/mol) + 3(16 g/mol))
= 12.5 mol
31. ΔGo = ΣΔGof (Products) - ΣΔGof (Reactants)
= [0 + 2(-394.36) + 4(-228.57)] - [210 + 2(97.54)]
= -2108 kJ/mol
ΔGo = -RTlnKeq
-2108 = -(8.314)(273)lnKeq
Keq = e929
Keq is very large and ΔGo is negative. This is a spontaneous reaction.
32. 5 protons + 5 neutrons → 10B
Δm
= Σ m(products) - Σ m(reactants)
= (10.0129) - [5(1.0078) + 5(1.0087)]
= -6.96 x 10-2 u
Δm
= (-6.96 x 10-2 u)(1.6605 x 10-27 kg/u)
= -1.155708 x 10-28 kg
E = mc2 = (-1.155708 x 10-28 kg)(3.00 x 108 m/s)2
= -1.04 x 10-11 J for 10 nucleon
1.04 x 10-12 J per nucleon
= ΣΔGof (Products) - ΣΔGof (Reactants)
= 98.28 - 2(51.8)
= -5.32 kJ/mol
o
ΔG
= -RTlnKp
b)
(1000)(-5.32) = -(8.314)(298)lnKp
lnKp = 2.147
Kp
= 8.56
34. a)
Sn + 2Ag+ → Sn2+ + 2Ag
b)
0.94 V
c)
Ecell = Eo - (0.0591/n) logQ
1.12 = 0.94 - (0.0591/2) log [Sn2+]/[0.35]2
[Sn2+] = 9.92 x 10-8 M
35. (No answer.)
36. ln(k1/k2) = Ea/R[1/T2 - 1/T2]
ln[(6.47 x 10-13)/k2] = (84,000 J)/(8.314 J/Kmol)[1/(393) - 1/(298)]
k2 = 2.35 x 10-9
33. a)
ΔGo
17