FACULTY OF SCIENCE
MARCH 18, 2011. 6:30 TO 8:30 PM
Examiners: Prof. B. Siwick Name:_________________________
Prof. A. Mittermaier
Dr. A. Fenster
Associate Examiner: A. Fenster
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2. This examination comprises 30 questions but will be marked out of
31 (see point 1 above). All questions are of equal value.
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Page 1 of 16 1. The heat of fusion for water is 6.01 kJ/mol and for ethyl alcohol is 5.01 kJ/mol. The
amount of heat that would melt 25.0 grams of water would melt how many grams of
ethyl alcohol (C H OH) ?
a) 8.2 g
b) 53.3 g
c) 76.7 g
d) 32.0 g
e) 11.7 g
2. Which compound is most likely to be soluble in both water and benzene?
a) propyl alcohol 3 7H OH)
b) hexane (6 14)
c) calcium chloride (Ca2l )
d) naphthalene (10 8)
e) toluene (7 8 )
3. The equilibrium constants for the chemical reaction:
N 2g) + O2(g) ↔ 2NO (g)
are Kp = 1.1 × 103 and 3.6 × 103 at 2,200 K and 2,500 K respectively. Which one of
the following statements is true?
a) Higher total pressure shifts the equilibrium to the left.
b) The partial pressure of NO(g) is less at 2,200 K than at 2,500 K.
c) The total pressure at 2,200 K is the same as at 2,500 K.
d) The reaction is exothermic; i.e. ΔH° < 0.
e) K is less than K by (RT).
4. For the reaction2 H (g)2+ I (g) ↔ 2 HI(gc, K = 92.0. When equilibrium
concentrations of HI and I are [HI] = 0.115 M and [I ] = 0.250 M, the equilibrium
concentration of [2 ] is:
a) 0.135 M
b) 5.75 × 10 M
c) 1.74 × 10 M
d) 9.56 M
e) 5.00 × 10 M
Page 2 of 16 5. A total of 0.12 g of a compound is dissolved in 10.0 g benzene. The resulting solution
freezes at 4.62 °C. Pure benzene freezes at 5.48 °C and has a freezing point depression
constant of K = 4.90 °C/m. What is the molecular mass of the compound, assuming it is
not an electrolyte?
a) 68 g mol-1
b) 106 g mol
c) 570 g mol-1
d) 11 g mol
e) 57 g mol-1
6. For the formation of NO2, Kc= [NO ]2/([NO] [O ]).2At equilibrium in a 2.50 L
container, there are 3.00 mol NO, 4.00 mol O2
and 22.0 mol NO .2The value of K cs:
7. A reaction is always spontaneous if:
i) ΔG is a negative value
ii) both enthalpy and entropy increase
iii) ΔH is negative and ΔS is positive
iv) both enthalpy and entropy decrease
v) ΔH is positive and ΔS is negative
a) i and iii
b) cannot be determined without temperature
c) i and ii
d) iii and iv
e) ii and v
8. Henry’s Law constants for aqueous solutions at 25 °C are 8.20 × 10 molal/mmHg for
N 2nd 1.62 × 10 -6molal/mmHg for O . 2etermine the solubility of nitrogen in water
under an atmospheric pressure of 760 mmHg, assuming that air is 80% N 2nd 20% O , 2
a) 4.99 × 10-4m
b) 1.23 × 10-3m
c) 6.23 × 10-4m
d) 1.25 × 10 m
e) 5.16 × 10-3m
Page 3 of 16 9. The element oxygen was prepared by Joseph Priestley in 1774 by heating mercury(II)
HgO(s) ↔ Hg(l) + ½O (g2 ΔH° = 90.84 kJ
Use the data given below to estimate the temperature at which this reaction will become
spontaneous under standard state conditions.
S°(Hg) = 76.02 J/K⋅mol
S°(O2) = 205.0 J/K⋅mol
S°(HgO) = 70.29 J/K⋅mol
a) 840 K
b) 108 K
c) 620 K
d) 430 K
e) 775 K
10. Commercial perchloric acid is 70.0% by mass, HClO (aq), and has a density of 1.67
g/mL. Calculate the molarity of perchloric acid in the solution, assuming the molecular
weight of HClO i4 100.5 g/mol.
a) 23.7 M
b) 1.17 M
c) 16.5 M
d) 0.12 M
e) 11.6 M
11. The following reaction is exothermic:
2N 2(g) → 2N (g2 + O (g)2
This means the reaction
a) will be spontaneous only at low temperatures.
b) is not spontaneous at any temperature.
c) will be spontaneous only at high temperatures.
d) will be spontaneous at all temperatures.
e) none of the above
12. If ΔG is positive for a certain reaction at a given T and P, then:
a) the reaction is endothermic
b) the reaction is spontaneous at high temperatures.
c) one would need to know the Kelvin temperature to determine spontaneity.
d) the reverse of the reaction is spontaneous.
e) the system is in equilibrium.
Page 4 of 16 13. For Cl2O(g) + 3/2 O2(g) → 2 ClO 2 ΔH° = 126 kJ/mol and ΔS° = -74.9 J/mol-K at
377 °C. What is Keq
b) 6.12 × 107
c) 9.17 × 1015
d) 4.27 × 1022
e) 1.07 × 10
14. Consider the following reaction:
C(s) + H2O(g) ↔CO(g) + H (g2
At equilibrium at a certain temperature, [H O(g)] = 0.12 M, and [CO(g)] = [H (g)] = 1.2
M. If suddenly these concentrations are increased by 0.50 M, which of the following is
a) more H2O(g) will be formed
b) Kc= 4.66
c) Since Kcdoes not change, nothing happens.
d) more products are formed
e) All the additional H O(g) is consumed
15. Given the following:
I) N O(g) + 1/2 O (g) ↔ 2NO(g) K = 1.7 × 10 -13
2 2 c
II) N2(g) + O2(g) ↔ 2NO(g) K c 4.1 × 10 -31
Find the value of the equilibrium constant for the following equilibrium reaction:
N 2g) + 1/2 O2(g) ↔N O2g)
a) 7.0 × 1044
b) 1.6 × 10
c) 2.4 × 1018
d) 2.6 × 10
e) 4.2 × 107
16. Calculate the temperature at whicheq for a reaction is 1.04 × 10 if ΔH° = -83.2
kJ/mol and ΔS° = -246 J/mol ∙ K.
a) 307 K
b) 274 K
c) 0.274 K
d) cannot be determined without ΔG°
e) 0.307 K
Page 5 of 16 17. The vapor pressures of pure hexane and pure heptane at 25 °C are 151.4 mmHg and
45.62 mmHg respectively. An ideal solution contains 0.700 mol fraction hexane and
0.300 mol fraction heptane. What is the composition of the vapor in equilibrium with this
solution at 25 °C?
a) 70.0% hexane, 30.0% heptane
b) 88.6% hexane, 11.4 % heptane
c) 23.2% hexane, 76.8% heptane
d) 76.8% hexane, 23.2% heptane
e) 11.4% hexane, 88.6% heptane
18. Consider the following reaction at equilibrium:
2SO 2g) + O (2) ↔ 2SO (g)3ΔH° = -196.6 kJ/mol
The equilibrium is displaced to the left if: