A Chem 16 Sample Exam Answer Key created by J4 for the DLRC Review on February 4, 2011

1. THERMODYNAMICS
1. Which of the following phase changes is exothermic?
a) condensation
b) evaporation
c) fusion
d) sublimation
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2. Which of the following substances has a ∆Hf = 0
a) C(diamond)
b) O3(g)
-
c) Br (g)
d) Ag(s)
3. A positive change in entropy is a result of
a) a decrease in temperature of a system consisting of a gaseous mixture.
b) the freezing of liquid water.
c) an increase in the number of gaseous molecules after a chemical reaction.
d) a process that cannot occur spontaneously.
4. Which is true about the value of ∆S when 0.5 mole of CH4 undergoes the following reaction, CH4 (g) + 3Cl2 (g) → CH3Cl3 (l) + 3HCl (g)?
a) It is a positive value.
b) It is a negative value
c) It is zero.
d) It is dependent on the value of the entropy of the reaction.
e) The value cannot be determined.
5. Which of the following reactions will exhibit a decrease in Gibb’s free energy at 298 K?
a) Neutralization reaction.
-
b) Reaction of bromide (Br ) with chlorrine (Cl2) water.
2+
c) Reaction of Cu with excess NH3.
d) All of the above.
6. At boiling point of water, i.e., H2O(l) H2O(g), the
a) ∆G=0 for the process
b) ∆S=0 for the process
c) ∆H=0 for the process
d) ∆E=0 for the process
7. Which of the following conditions would ALWAYS result to a spontaneous reaction?
a) ∆H > 0, ∆S > 0
b) ∆H > 0, ∆S < 0
c) ∆H < 0, ∆S > 0
d) ∆H < 0, ∆S < 0
8. Calculate the standard enthalpy of formation of gaseous HCl from the following data:
o
NH3(g) + HCl(g) → NH4Cl(s) ∆H = -176.0 kJ
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N2(g) + 3 H2(g) → 2 NH3(g) ∆H = - 92.22 kJ
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N2(g) + 4 H2(g) + Cl2(g) → 2 NH4Cl(s) ∆H = - 628.86 kJ
ANSWER: -184.64 KJ
9. One of the cleanest burning hydrocarbon is a compound called 2,3,4-trimethylpentane, which has a formula C8H18 (l). The complete
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combustion of 1 mole of this compound to gaseous products leads to ∆H = -5069 KJ. Write the balanced thermochemical equation for
the combustion of 1 mole of C8H18 (l).
ANSWER: C8H18 + 25/2O2 8CO2 + 9H2O + 5069 KJ
10. The heat of combustion of fructose, C6H12O6, (MW = 180 g/mol) is -2812 KJ/molfructose. A fresh golden delicious apple weighing
6
120g contains 16.0 g fructose. How many apples do you need to eat to obtain energy equivalent to 1.249 x 10 J?
a) 3
b) 4
c) 5
d) 6

2. For numbers 12-13. Methanol, CH3OH, (MW = 31 g/mol) is an efficient fuel with a high octane rating that can be produced from coal
and hydrogen.
CH3OH(g) + 3/2O2(g) → CO2(g) + 2H2O(l) ∆H = - 764 kJ/mol
11. What is the amount of the heat evolved when 110.0 g CH3OH(g) burns in excess oxygen.
a) 4.46KJ
b) 215 KJ
c) 2711 KJ
d) 23684KJ
12. What mass of O2 (MW = 32 g/mol) is consumed when 975 kJ of heat is given out?
a) 0.0163 g
b) 0.0245 g
c) 40.8 g
d) 61.3 g
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13. How much heat is required to raise the temperature of 78.2 g of water from 10.0 C to 32.0 C. The specific heat of water is 4.184
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J/g C.
a) 7.20 KJ
b) 96.6 KJ
c) 10.5 KJ
d) 3.27 KJ
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14. When 75.0 grams of metal at 75.0 C is added to 150 grams of water at 15.0 C, the temperature of the water rises to 18.3 C. What
is the specific heat of the metal? Assume that the heat transfer is just between the metal and water. The specific heat of water is 4.184
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J/g C.
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a) 2.35 x 10 J/g C
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b) 0.460 J/g C
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c) 0.487 J/g C
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d) 144 J/g C
15. Methylhydrazine, CH6N2, is commonly used as a liquid rocket fuel. The combustion of methylhydrazine with oxygen produces N2 (g),
CO2 (g), and H2O (l):
2CH6N2 (l) + 5O2 (g) 2N2 (g) + 2CO2 (g) + 6H2O(g)
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When 4.00g of methylhydrazine is combusted in a bomb calorimeter, the temperature of the calorimeter increases from 25.00 C to
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39.50 C. In a separate experiment, the heat capacity of the calorimeter is measured to be 7.794 KJ/ C. What is the heat of reaction for
the combustion of a mole of CH6N2 in the calorimeter?
a) +1302 KJ/mol
b) -1302 KJ/mol
c) +89.83 KJ/mol
d) -89.83 KJ/mol
e) 7.794 KJ/mol
16. What is ∆H° of the reaction: C6H6 (l) + 15/2O2 (g) → 6CO2 (g) + 3H2O (l)? The heat of formation of the substances involve is
summarized in the table below.
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Substances ∆Hf (kJ / mol)
C6H6 49.0
CO2 -393.5
H2O -285.8
a) -3267 KJ/mol
b) +3267 KJ/mol
c) +3169 KJ/mol
d) -3169 KJ/mol
e) 0 KJ/mol
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For numbers 8 and 9, consider the data below (all values are at 25 C).
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∆Hf (kJ / mol) S (J / mol · K)
Fe(CO)5(l) –774.0 338.0
Fe(CO)5(g) –733.8 445.2
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17. What is ∆G for Fe(CO)5(l) → Fe(CO)5(g) at 298 K?
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a) -3.191 x 10 KJ/mol
b) -10.0 KJ/mol
c) +8.238 KJ/mol
d) +72.15 KJ/mol

3. 18. At what temperature will Fe(CO)5(l) start to vaporize (assuming the thermodynamic values are independent of temperature)?
a) 290 K
b) 298 K
c) 369 K
d) 375 K
19. Use bond energies to estimate the enthalpy of the following gas phase reaction: CH4(g) +3Cl2(g) CHCl3(g) +3HCl(g)
Average bond energies per
Bonds
mole of bonds (KJ)
C-H 413
Cl-Cl 242
H-Cl 432
C-Cl 339
a) -348 KJ/mol
b) +348 KJ/mol
c) -529 KJ/mol
d) +529 KJ/mol
e) -909 KJ/mol
20. Which is not a state function
a) Enthalpy
b) Entropy
c) Heat
d) Gibbs free energy
ELECTRONIC STRUCTURE
1. Which of the following states that each electron has a unique set of quantum number.
a) Heisenberg Uncertainty Principle
b) Aufbau Principle
c) Pauli Exclusion Principle
d) Hund’s Rule
2. Which of the quantum numbers determines the location of the electrons in space?
a) Principal quantum number
b) Azimuthal quantum number
c) Magnetic quantum number
d) Electron spin quantum number
3+
3. Which is the correct electron configuration of 26Fe ?
2 6
a) [Ar] 4s 3d
2 3
b) [Ar] 4s 3d
0 5
c) [Ar] 4s 3d
d) 2 6 3
[Ar] 4s 3d 4p
e) None of the above
2-
4. Which is the correct electron configuration of 8O ?
2 4
a) [He] 2s 2p
2 6
b) [He] 2s 2p
2 2
c) [He] 2s 2p
0 4
d) [He] 2s 2p
e) None of the above
5. What is the quantum number for the last entering electron of 28Ni
ANSWER: n=3; l=2; ml=0; ms=-1/2
6. Which of the following is a CORRECT set of quantum numbers?
a) n = 2, ℓ = 0, mℓ = 1, ms = –½
b) n = 4, ℓ = 2, mℓ = –3, ms = +½
c) n = 3, ℓ = 3, mℓ = 0, ms = ½
d) n = 4, ℓ = 2, mℓ = –1, ms = +½
e) All are not allowed

4. 7. Which of the following is diamagnetic?
a) 13Al
b) 11Na
c) 37Rb
2+
d) 12Mg
8. Which has the most number of unpaired electrons in the ground state?
a) 7N
b) 8O
c) 16S
d) 17Cl
9. Which of the following pair is not isoelectronic?
a) - 3-
F and N
b) 2- 2+
O and Sr
2+
c) Ne and Mg
3+ +
d) Al and Na
PERIODIC TRENDS
Arrange the given elements in each number in the decreasing order (from the largest value followed by the second largest and then the
smallest).
Given Answer
1. Atomic radius: Ba, Ta, Cr Ba> Ta> Cr
2. Electronegativity: P, Si, O O> P> Si
3. Ionization energy: Sn, Te, Sb Te> Sb> Sn
4. Electron affinity (from N, P, Al N> P> Al
most to least negative):
5. Metallic property: Ge, Cd, Cl Cd> Ge> Cl
CHEMICAL BONDING ANG MOLECULAR GEOMETRY
1. Which contains a central atom that does not follow the octet configuration?
+
a) H3O
b) BBr3
+
c) NF4
2-
d) CO3
e) CO2
2. Which is the most polar covalent bond?
a) C-Br
b) C-F
c) C-N
d) C-O
3. Which molecule is non-polar?
a) PCl3
b) CCl4
c) OF2
d) H2S
4. Which of the following has the most number of lone pairs at the central atom?
a) XeF4
b) PCl5
c) SF6
-
d) I3
e) SF4
5. What is the molecular geometry of ClF3?
a) Trigonal planar
b) See-saw
c) Trigonal bipyramidal
d) T-shaped

5. 6. What is the electron group geometry of BrF5?
a) See-saw
b) Square pyramidal
c) Octahedral
d) Trigonal bipyramidal
For 7-11, refer to the lewis structure below.
7. How many σ and π bonds are present in the molecule?
a) 14σ and 0π bonds
b) 15σ and 2π bonds
c) 14σ and 3π bonds
d) 15σ and 5π bonds
8. What is the molecular geometry group of oxygen C?
a) Tetrahedral
b) Angular
c) Trigonal pyramidal
d) See-saw
9. Which of the following has the largest bond angle?
a) H-Ca-H
b) Ce-Cf-N
c) O-Cb-O
d) H-Ce-Cf
10. Which of the following has the shortest bond?
a) Cd-H
b) Cf-N
c) Cb-O
d) Oc-Cd
11. What are the orbital overlaps involved in the sigma bonds at Ce?
3 3 3 3 2
a) sp -sp , sp -s, and sp -sp
3 3
b) sp -sp only
2 2 2 3 3 3
c) sp -sp , sp -sp , and sp -sp
3 3 3 3
d) sp -sp , sp -s, and sp -sp
12. Which of the following is diamagnetic?
a) O2
2-
b) O2
+
c) O2
d) None of the above
13. What is the bond order of O2?
a) 1
b) 2
c) 3
d) 4
14. What is the HOMO and LUMO of O2?
* * *
a) HOMO= 2π py and 2π pz; LUMO= 2σ px
* *
b) HOMO= 2π py and 2π pz; LUMO= 2πpy and 2πpz
*
c) HOMO= 2σ px; LUMO= 2σpx
d) HOMO= 2πpy and 2πpz ;LUMO= 2σpx

6. 15. Which of the following does not exist?
a) He2
+
b) He2
c) H2
d) None of the above