1. No category

CLAS Chem 1B
1.
Practice Final
Which one of the following statements is false?
A) The change in internal energy, E, for a process is equal to the amount of heat absorbed at
constant volume, qv.
B) The change in enthalpy, H, for a process is equal to the amount of heat absorbed at constant
pressure, qp.
C) A bomb calorimeter measures H directly.
D) If qp for a process is negative, the process is exothermic.
E) The freezing of water is an example of an exothermic reaction
2. Calculate E for a system that releases 24 J of heat while 57 J of work is done on it.
A) 33 J
B) 81 J
C) –81 J
D) –33 J
E) 24 J
3. One mole of an ideal gas is expanded from a volume of 1.50 L to a volume of 10.18 L against a
constant external pressure of 1.03 atm. Calculate the work. (1 L• atm = 101.3 J)
A) –8.79  102 J
B) –8.94 J
C) –9.06  102 J
D) –0.0883 J
E) 9.06 J
4. Which of the following are state functions?
A) work, heat
B) work, heat, enthalpy, energy
C) enthalpy, energy
D) work, heat, enthalpy
E) heat, enthalpy, energy
5. Consider the reaction
C2H5OH(l) + 3O2(g)  2CO2(g) + 3H2O(l), H = –1.37  103 kJ
When a 15.6-g sample of ethyl alcohol (molar mass = 46.1 g/mol) is burned, how much energy is
released as heat?
A)
B)
C)
D)
E)
87.8 kJ
2.14  104 kJ
4.64  102 kJ
4.05  103 kJ
4.75 kJ
6. Consider a process carried out on 1.00 mol of a monatomic ideal gas by the following pathway:
A (3.00 atm, 20.0 L) to B (3.00 atm, 50.0 L) to C (1.00 atm, 50.0 L). Calculate HABC.
A) -25 L•atm
B) 25 L•atm
C) -475 L•atm
D) 475 L•atm
E) none of these
7. A calorimeter contains 123 g of water at 27.0°C. A block of metal with a mass of 28 g is heated to
95.8°C and then placed in the water in the calorimeter. After sufficient time, the temperature of the
water is measured and found to be 28.8°C. Calculate the heat capacity per gram of metal. Assume no
heat is lost to the calorimeter or the surroundings.
A) 2.0 J/g°C
B) 0.12 J/g°C
C) 6.8  102 J/g°C
D) 0.49 J/g°C
E) 0.026 J/g°C
8. A calorimeter contains 142 g of water at 22.5°C. A 12-g sample of NaCl is added to the water in the
calorimeter. After the solid has dissolved, the temperature of the water is 21.4°C. Calculate the
enthalpy of solution for dissolving sodium chloride. Assume that no heat is lost to the calorimeter or
the surroundings and that the specific heat of the solution is the same as that of pure water (4.18 J/g C).
A) 0.71 kJ/mol
B) 0.83 kJ/mol
C) 3.2 kJ/mol
D) 3.5 kJ/mol
E) 0.059 kJ/mol
9. The heat of combustion of acetylene, C2H2(g), at 25°C, is –1299 kJ/mol. At this temperature, H°f
values for CO2(g) and H2O(l) are –393 and –286 kJ/mol, respectively. Calculate H°f for acetylene.
A) 2376 kJ/mol
B) 625 kJ/mol
C) 227 kJ/mol
D) –625 kJ/mol
E) none of these
10. Which of the following is true?
A) As long as the disorder of the surroundings is increasing, a process will be spontaneous.
B) For any process, Ssurr and Ssys have opposite signs.
C) If Ssurr = -Ssys , the process is at equilibrium.
D) H° is zero for a chemical reaction at constant temperature.
E) none of these
11. At 25°C, the following heats of reaction are known:
2C2H2 + 5O2  4CO2 + 2H2O
H = –2600.0 kJ
C + O2  CO2
H = –394 kJ
2H2 + O2  2H2O
H = –572 kJ
At the same temperature, calculate H for the following reaction:
2C + H2  C2H2
A)
B)
C)
D)
E)
H = ?
226 kJ
-226 kJ
2422 kJ
-2422kJ
none of these
12. Which of the following result(s) in an increase in the entropy of the system?
I. (See diagram.)
II. Br2(g)  Br2(l)
III. NaBr(s)  Na+(aq) + Br–(aq)
IV. O2(298 K)  O2(373 K)
V. NH3(1 atm, 298 K)  NH3(3 atm, 298 K)
A)
B)
C)
D)
E)
I
II, V
I, III, IV
I, II, III, IV
I, II, III, V
13. The dissolution of ammonium nitrate occurs spontaneously in water at 25 °C. As NH4NO3
dissolves, the temperature of the water decreases. What are the signs of ΔHrxn, ΔSrxn, and ΔGrxn for
this process?
A) ΔHrxn > 0, ΔSrxn < 0, ΔGrxn > 0
B) ΔHrxn > 0, ΔSrxn > 0, ΔGrxn < 0
C) ΔHrxn > 0, ΔSrxn > 0, ΔGrxn > 0
D) ΔHrxn < 0, ΔSrxn < 0, ΔGrxn < 0
E) ΔHrxn < 0, ΔSrxn > 0, ΔGrxn > 0
14. The molar entropy of CH4 (g) is 189 J mol-1 K-1 at 25oC and 1 atm pressure. Assuming ideal gas
behavior, calculate the entropy of 0.27 mol CH4 (g) at 25oC and a volume of 28.8 L.
A) 54.3 J K-1
B) 192.3 J K-1
C) 201.2 J K-1
D) 51.0 J K-1
E) none of these
Use the following to answer questions 15-17:
One mole of an ideal gas is compressed isothermally and reversibly at 607.4 K from 5.60 atm to 8.90
atm.
15. Calculate q.
A) 298 kJ
B) -2.34 kJ
C) 2.34 kJ
D) -298 kJ
E) none of these
16. Calculate w.
A) 298 kJ
B) -2.34 kJ
C) 2.34 kJ
D) -298 kJ
E) none of these
17. Calculate H.
A) 0 kJ
B) -2.34 kJ
C) 2.34 kJ
D) 3.85 kJ
E) none of these
18. A 92.1 gram sample of water is heated from 314 K to its boiling point of 373 K at a constant
pressure. The water is then completely boiled at a constant pressure. What is the change in entropy ΔS
for this process? The heat of vaporization of water is 40.7 kJ/mol and Cp (liquid water) = 75.3 J/ K
mol.
A) 122.1 J/K
B) 624.6 J/K
C) –492 J/K
D) 66.9 J/K
E) none of these
19. The dissociation of hydrogen
H2(g)
A) is spontaneous at any temperature.
B) is spontaneous at high temperature.
C) is spontaneous at low temperature.
D) is independent of temperature.
E) never takes place.
2H(g)
20. Consider the following reaction at 25 °C: N2 (g) + 3 H2 (g) < ---> 2 NH3 (g)
Initially, PN2 = 0.4 atm, PH2 = 0.8 atm, and PNH3 = 1.3 atm. At equilibrium, the partial pressure of H2
has increased to 1.4 atm. What is the sign of ΔG˚ for this reaction?
A) ΔG˚> 0
B) ΔG˚< 0
C) ΔG˚= 0
D) more information is needed
21. Consider the reaction
2N2O5(g)
4NO2(g) + O2(g)
at 25°C, for which the following data are relevant:
S° (J/K•mol)
H°f (kJ/mol)
N2O5
11.29
355.3
NO2
33.15
239.9
O2
0
204.8
Calculate G° for the reaction at 25°C.
A) –135 kJ
B) 98.7 kJ
C) –25.2 kJ
D) –11.2 kJ
E) 0
22. Given
CH3CO2H(aq)
H+(aq) + CH3CO2–(aq)
at 25°C, Ka = 1.8  10–5
What is G at 25°C for a solution in which the initial concentrations are
[CH3CO2H]o = 0.10 M
[H+]o = 2.0  10–8 M
[CH3CO2–]o = 0.010 M
A)
B)
C)
D)
E)
+50. kJ
–50. kJ
+23 kJ
–23 kJ
27 kJ
23. At 1150 K the following reaction has a K of 0.365. Find the equilibrium constant for this
reaction at 1260 K.
2 SO2(g) + O2(g) → 2 SO3(g)
ΔH°= 198 kJ/mol
A) 0.366
B) 1.654
C) 0.0599
D) 2.225
E) None of these.
24. Which metal, Al or Ni, could reduce Zn2+ to Zn(s) if placed in a Zn2+(aq) solution?
E° = -0.76 V
Zn2+ + 2e-  Zn
2+
E° = -0.23 V
Ni + 2e  Ni
3+
E° = -1.66 V
Al + 3e  Al
A)
B)
C)
D)
E)
Al
Ni
Both Al and Ni would work.
Neither Al nor Ni would work.
This cannot be determined.
25. A voltaic cell consists of an Au/Au3+ electrode (E˚=1.50 V) and a Cu/Cu2+ electrode (E˚= 0.34 V).
Calculate [Au3+] if [Cu2+] = 1.20 M and Ecell = 1.13 V at 25 ˚C.
A) 0.001 M
B) 0.002 M
C) 0.01 M
D) 0.02 M
E) 0.04 M
26. Consider the following galvanic cell at 25°C.
Pt | Cr 2+ (0.42 M), Cr 3+ (3.4 M) || Co 2+ (0.22 M) | Co
The overall reaction and equilibrium constant value are given below. Calculate the cell potential, E, for
this galvanic cell.
2 Cr 2+ (aq) + Co 2+ (aq) → 2 Cr 3+(aq) + Co(s)
K = 2.79 x 107
a. 0.220 V
b. 0.174 V
c. 0.293 V
d. 0.147 V
e. 0.267 V
27. A Galvanic concentration cell is constructed with silver electrodes and Ag+ in each compartment.
In the anode compartment, [Ag+] = 0.071 M. What must be [Ag+] in the cathode compartment in order
to achieve a cell potential of 0.088 V at 298 K?
a) 2.73 M
b) 1.62 M
c) 0.0023 M
d) 2.19 M
e) none of these
28. Copper is electroplated from an aqueous CuSO4 solution. A constant current of 5.10 amp is applied
by an external power supply. How long will it take to deposit 4.08  102 g of Cu? The atomic mass of
copper is 63.546 g/mol.
A) 67.5 h
B) 33.7 h
C) 2.44 h
D) 135.0 h
E) 101.2 h
29. The rate constant k is dependent on
A) the concentration of the reactant.
B) the concentration of the product.
C) the temperature.
D) the order of the reaction.
E) none of these
Use the following to answer questions 30 and 31:
A general reaction written as 2A + 2B  C + 2D is studied and yields the following data.
[A]0
[B]0
Initial [C]/t
0.100 M
0.100 M
4.00  10–5 mol/L • s
0.200 M
0.100 M
4.00  10–5 mol/L • s
0.100 M
0.200 M
8.00  10–5 mol/L • s
30. What is the overall order of the reaction?
A) 1
B) 4
C) 3
D) 2
E) 0
31. What are the proper units for the rate constant for the reaction?
A) s–1
B) mol L–1 s–1
C) L mol–1 s–1
D) L3 mol–3 s–1
E) L2 mol–2 s–1
32. A first-order reaction is 43% complete at the end of 18 min. What is the value of the rate constant?
A) 3.1 x 10-2 min-1
B) 0.21 min-1
C) 0.031 min-1
D) 4.7  10-2 min-1
E) 1.4  10-2 min-1
33. The OH radical disproportionates according to the elementary chemical reaction
OH + OH  H2O + O. This reaction is second order in OH. The rate constant for the reaction is 2.4 
10–12 cm3/molecule • s at room temperature. If the initial OH concentration is 1.7  1013
molecules/cm3, what is the first half-life for the reaction?
A) 3.5  1024 s
B) 2.9  1011 s
C) 0.025 s
D) 4.9 s
E) 4.2 s
34. For which of the following is the half-life directly dependent on the concentration of the reactant?
A) zero-order reaction
B) first-order reaction
C) second-order reaction
D) two of these
E) all of these
35. Consider two reaction vessels, one containing A and the other containing B, with equal
concentrations at t = 0. If both substances decompose by first order kinetics where:
kA = 0.116 s-1 and kB = 1.136 s-1 . At what time will [A] = 2.3[B]?
A) never
B) 9.8 s
C) 1.91 s
D) 0.82 s
E) none of the above
36. Nitrogen dioxide reacts with carbon monoxide to produce nitrogen monoxide and carbon dioxide.
NO2(g) + CO(g) → NO(g) + CO2(g)
A proposed mechanism for this reaction is
2 NO2(g) → NO3(g) + NO(g)
( fast, equilibrium)
NO3(g) + CO(g) → NO2(g) + CO2(g)
(slow)
What is a rate law that is consistent with the proposed mechanism?
A) rate = k[NO2]2[CO] [NO]–1
B) rate = k[NO2]2[CO]
C) rate = k[NO2][CO]
D) rate = k[NO3][CO]
E) rate = k[NO2]2
37. According to collision theory, which condition(s) must be met in order for molecules to react?
1. The reacting molecules must collide with sufficient energy to initiate the process of breaking and
forming bonds.
2. A catalyst must be in contact with the reacting molecules for a reaction to occur.
3. The reacting molecules must collide with an orientation that can lead to rearrangement of the atoms.
A) 1 only
B) 2 only
C) 3 only
D) 1 and 2
E) 1 and 3
38. When ethyl chloride is dissolved in sodium hydroxide, it is converted into ethanol by the reaction
CH3CH2Cl + OH– → CH3CH2OH + Cl+
If the pre-exponential factor, A, is 3.4 × 1014 s–1 and the activation energy for the reaction is 100.0
kJ/mol, what will the rate constant be at 28°C?
A) 3.8 × 1014 s–1
B) 1.1 × 10–3 s–1
C) 8.9 × 102 s–1
D) 9.2 × 10–3 s–1
E) 1.5 × 10–3 s–1
39. Which of the following frequencies corresponds to light with the longest wavelength?
A) 3.00  1013 s–1
B) 4.12  105 s–1
C) 8.50  1020 s–1
D) 9.12  1012 s–1
E) 3.20  109 s–1
40. From the following list of observations, choose the one that most clearly supports the conclusion
that electrons in atoms have quantized energies.
A) the emission spectrum of hydrogen
B) the photoelectric effect
C) the scattering of alpha particles by metal foil
D) diffraction
E) cathode "rays"
41. For which of the following transitions does the light emitted have the longest wavelength
A) n = 4 to n = 3
B) n = 4 to n = 2
C) n = 4 to n = 1
D) n = 3 to n = 2
E) n = 2 to n = 1
42. Which of the following statements is(are) true?
I. An excited atom can return to its ground state by absorbing electromagnetic radiation.
II. The energy of an atom is increased when electromagnetic radiation is emitted from it.
III. The energy of electromagnetic radiation increases as its frequency increases.
IV. An electron in the n = 4 state in the hydrogen atom can go to the n = 2 state by emitting
electromagnetic radiation at the appropriate frequency.
V. The frequency and wavelength of electromagnetic radiation are inversely proportional to each
other.
A) II, III, IV
B) III, V
C) I, II, III
D) III, IV, V
E) I, II, IV
43. The energy change associated with the n = 2 to n = 1 electron transition in the hydrogen spectrum
is -1.64  10–18 J. By what coefficient should this be multiplied to obtain the energy change associated
with the same electron transition in the Li2+ ion?
A)
9
B)
7
C)
4
D)
3
E)
1
44. How many electrons can be described by the quantum numbers n = 4, l = 3, ml = 0?
A)
B)
C)
D)
E)
0
2
6
10
14
45. How many electrons can be described by the quantum numbers n = 6, l = 2, ml = 0, ms = 1?
A) 0
B) 2
C) 6
D) 10
E) 14
46. An element or ion has the electron configuration [Kr] 4d105s25p2. The correct choice is
A) In+
B) Zr
C) Sn
D) Te2E) Pb
47. Which atom has three 2p electrons in its ground state?
A) Si
B) As
C) N
D) P
E) none of these
48. How many unpaired electrons does chlorine have in its ground state?
A) 1
B) 2
C) 3
D) 17
E) none of these
Use the following to answer questions 49-50:
Consider the following orderings.
I. Al < Si < P < Cl
II. Be < Mg < Ca < Sr
III. I < Br < Cl < F
IV. Na+ < Mg2+ < Al3+ < Si4+
49. Which of these give(s) a correct trend in size?
A) I
B) II only
C) III
D) IV only
E) II, IV
50. Which of these give(s) a correct trend in ionization energy?
A) III only
B) I, II only
C) I, IV only
D) I, III, IV
E) none of them
51. What of the following shows the bonds in order of decreasing polarity?
A) N-Cl, P-Cl, As-Cl
B) P-Cl, N-Cl, As-Cl
C) As-Cl, N-Cl, P-Cl
D) P-Cl, As-Cl, N-Cl
E) As-Cl, P-Cl, N-Cl
52. In which case is the bond polarity incorrect?
A) + H–F –
B) + Na–O –
C) + Mg–H –
D) + Cl–Br –
E) + C–O –
53. Given the following bond energies:
C–C 347 kJ/mol
C=C 614 kJ/mol
C–O 358 kJ/mol
C=O 745 kJ/mol
C–H 413 kJ/mol
O–H 463 kJ/mol
O–O 146 kJ/mol
Estimate H for the reaction H2O2 + CH3OH  H2CO + 2H2O.
A)
B)
C)
D)
E)
–291 kJ
–145 kJ
–287 kJ
+145 kJ
+291 kJ
Draw the Lewis structures of the molecules below, and use them to answer the following questions.
I.
BH3
II. NO2
III. SF6
IV. O3
V. PCl5
54. Which of the molecules obeys the octet rule?
A) I
B) II
C) III
D) IV
E) V
55. How many resonance structures does the molecule O3 have?
A) 0
B) 1
C) 2
D) 3
E) 4
56. True or False: In the O3 molecule, all the atoms have a formal charge of zero.