1
General Chemistry II
Exam 1 Practice Problems
Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.
____
1. How much heat is released when 75 g of octane is burned completely if the enthalpy of combustion is -5,500 kJ/mol
C8H18?
C8H18 + 25/2 O2 → 8CO2 + 9H2O
a.
b.
c.
d.
e.
____
7200 kJ
8360 kJ
4.1 × 105 kJ
3600 kJ
5500 kJ
2. Calculate the amount of heat released in the complete combustion of 8.17 grams of Al to form Al2O3(s) at 25°C and 1
atm. ∆H for Al2O3(s) = 1676 kJ/mol
4Al(s) + 3O2(g) → 2Al2O3(s)
a.
b.
c.
d.
e.
____
254 kJ
203 kJ
127 kJ
237 kJ
101 kJ
3. Given the following at 25°C and 1.00 atm:
∆H0
33.2 kJ
11.1 kJ
1/2N2(g) + O2(g) → NO2(g)
N2(g) + 2O2(g) → N2O4(g)
Calculate the ∆H0 for the reaction below at 25°C.
2NO2(g) → N2O4(g)
a.
b.
c.
d.
e.
____
+11.0 kJ
+44.3 kJ
+55.3 kJ
-22.1 kJ
-55.3 kJ
4. Calculate ∆H0 for the following reaction at 25.0°C.
∆H (kJ/mol)
a.
b.
c.
d.
e.
-263 kJ
54 kJ
19 kJ
-50 kJ
109 kJ
Fe3O4(s)
-1118
+ CO(g)
-110.5
→
3FeO(s)
-272
+ CO2(g)
-393.5
2
____
5. How much heat is released when 6.38 grams of Ag(s) reacts by the equation shown below at standard state conditions?
4Ag(s) + 2H2S(g) + O2(g) → 2Ag2S(s) + 2H2O(l)
Substance
Ag(s)
H2S(g)
O2(g)
Ag2S(s)
H2O(l)
a.
b.
c.
d.
e.
____
0
-20.6
0
-32.6
-285.8
8.80 kJ
69.9 kJ
22.1 kJ
90.8 kJ
40.5 kJ
6. Evaluate ∆H0 for the following reaction from the given bond energies.
2HBr(g) → H2(g) + Br2(g)
∆HH-H = 436 kJ/mol, ∆HBr-Br = 193 kJ/mol, ∆HH-Br = 366 kJ/mol
a.
b.
c.
d.
e.
-103 kJ
-143 kJ
+103 kJ
+142 kJ
259 kJ
____
7. A 0.900-g sample of toluene, C7H8, was completely burned in a bomb calorimeter containing 4560. g of water which
increased in temperature from 23.800°C to 25.718°C. What is ∆E for the reaction in kJ/mol C7H8? The heat capacity of
the calorimeter was 780. J/°C. The specific heat of water is 4.184 J/g•°C.
a. - 4520 kJ/mol
b. +3500 kJ/mol
c. -38.1 kJ/mol
d. -2220 kJ/mol
e. -3900 kJ/mol
____
8. Calculate ∆S0 for the reaction below at 25°C. S0 for SiH4 = 204.5 J/mol•K, for O2(g) = 205.0 J/mol•K, for SiO2(s) =
41.84 J/mol•K, for H2O(l) = 69.91 J/mol•K.
SiH4(g) + 2O2(g) → SiO2(s) + 2H2O(l)
a.
b.
c.
d.
e.
____
-353.5 J/K
- 432.8 J/K
595.0 J/K
-677.0 J/K
-880.3 J/K
9. Which one of the following reactions has a positive entropy change?
a. H2O(g) → H2O(l)
b. BF3(g) + NH3(g) → F3BNH3(s)
c. 2SO2(g) + O2(g) → 2SO3(g)
d. N2(g) + 3H2(g) → 2NH3(g)
e. 2NH4 NO3(s) → 2N2(g) + 4H2O(g) + O2(g)
3
____
10. Consider the conversion of a substance from solid to liquid.
Solid
Liquid
At one atmosphere pressure and at the melting point of the substance, __________.
a. ∆H = 0 for the process
b. ∆S = 0 for the process
c. ∆E = 0 for the process
d. ∆G = 0 for the process
e. both ∆H = 0 and ∆E = 0 for the process
____
11. Calculate the ∆G at 298 K for PbCl2(s) from the following information. ∆G0 for the reaction below is -58.4 kJ at 298 K.
∆G (kJ/mol)
a.
b.
c.
d.
e.
____
PbS(s)
-98.7
+ 2HCl(g)
-95.30
→
PbCl2(s)
?
+ H2S(g)
-33.6
-16.0 kJ/mol
- 47.6 kJ/mol
-314.1 kJ/mol
-36.2 kJ/mol
-52.3 kJ/mol
12. For the reaction given below, ∆H0 = -1516 kJ at 25°C and ∆S0 = - 432.8 J/K at 25°C. This reaction is spontaneous
__________.
SiH4(g) + 2O2(g) → SiO2(s) + 2H2O(l)
a.
b.
c.
d.
e.
only below a certain temperature
only above a certain temperature
at all temperatures
at no temperatures
cannot tell from the information available
____
13. Which of the following reactions is spontaneous at relatively low temperatures?
a. NH4Br(s) + 188 kJ → NH3(g) + Br2(l)
b. NH3(g) + HCl(g) → NH4Cl(s) + 176 kJ
c. 2H2O2(l) → 2H2O(l) + O2(g) + 196 kJ
d. both (a) and (b)
e. both (a) and (c)
____
14. For a certain process at 127°C, ∆G = -16.20 kJ and ∆H = -17.0 kJ. What is the entropy change for this process at this
temperature? Express your answer in the form, ∆S = __________ J/K.
a. -6.3 J/K
b. +6.3 J/K
c. -2.0 J/K
d. +2.0 J/K
e. -8.1 J/K
____
15. Evaluate ∆S0 for the reaction below at 25°C.
∆H (kJ/mol)
CH4(g)
-74.81
+ 2Cl2(g)
0
∆G (kJ/mol)
-50.75
0
→
CCl4(l)
-135.4
+ 2H2(g)
0
-65.27
0
4
a.
b.
c.
d.
e.
____
-360 J/K
-66.9 J/K
-155 J/K
- 487 J/K
-387 J/K
16. Estimate the temperature above which this reaction is spontaneous. ∆S0 = 16.1 J/K.
CH4(g) + N2(g) + 163.8 kJ → HCN(g) + NH3(g)
a.
b.
c.
d.
e.
9.91°C
1045 K
9.90 × 103°C
10.7 K
10.1°C
____
17. For which of the following substances does
a. CO2(g)
b. H2O(g)
c. Na(s)
d. Br2(g)
e. C(diamond)
____
18. Which of the following techniques cannot be used to calculate ∆Hrxn?
a. Calorimetry
b. Using melting points of reactants and products
c. Hess's Law
d. Using of Heats of Formation of reactants and products
e. Using bond energies of reactants and products
____
19. Which statement concerning sign conventions for ∆E = q + w is false?
a. For heat absorbed by the system, q is positive.
b. For work done by the system, w is negative.
c. When energy is released by the reacting system, ∆E is negative.
d. If ∆E is positive, energy can be written as a product in the equation for the reaction.
e. For an expansion, w is negative.
____
20. A system is compressed from 50.0 L to 5.0 L at a constant pressure of 10.0 atm. What is the amount of work done?
a. 2.5 × 105 J
b. 450 J
c. 4.6 × 104 J
d. -450 J
e. -4.6 × 104 J
= 0?
____ 21. A 1.00-g sample of hexane, C6H14, undergoes complete combustion with excess O2 in a bomb calorimeter.
The temperature of the 1500. g of water surrounding the bomb rises from 22.64°C to 29.30°C. The heat
capacity of the calorimeter is 4.04 kJ/°C. What is ∆E for the reaction in kJ/mol of C6H14. The specific heat of
water is 4.184 J/g•°C.
a. -9.96 × 103 kJ/mol
b. - 4.52 × 103 kJ/mol
c. -1.15 × 104 kJ/mol
d. -7.40 × 104 kJ/mol
e. -5.91 × 103 kJ/mol
5
____ 22. Assuming the gases are ideal, calculate the amount of work done, in joules, for the conversion of 1.00 mole of
Ni to Ni(CO)4 at 75°C in the reaction below. The value of R is 8.314 J/mol•K.
Ni(s) + 4CO(g) → Ni(CO)4(g)
a.
b.
c.
d.
e.
1.80 × 103 J
8.68 × 103 J
-1.80 × 103 J
-8.68 × 103 J
- 494 J
6
General Chemistry II
Answer Section
Exam 1 Practice Problems
MULTIPLE CHOICE
1. ANS: D
TOP: Thermochemical Equations
2. ANS: A
TOP: Standard Molar Enthalpies of Formation...
3. ANS: E
TOP: Hess's Law
4. ANS: C
TOP: Hess's Law
5. ANS: A
TOP: Hess's Law
6. ANS: C
TOP: Bond Energies
7. ANS: E
TOP: Changes in Internal Energy, Delta E
8. ANS: B
TOP: Entropy
9. ANS: E
TOP: Entropy
10. ANS: D
TOP: Free Energy Change, Delta G, and Spontaneity
11. ANS: C
TOP: Free Energy Change, Delta G, and Spontaneity
12. ANS: A
TOP: The Temperature Dependence of Spontaneity
13. ANS: B
TOP: The Temperature Dependence of Spontaneity
14. ANS: C
TOP: The Temperature Dependence of Spontaneity
15. ANS: C
TOP: The Temperature Dependence of Spontaneity
16. ANS: C
TOP: The Temperature Dependence of Spontaneity
17. ANS: C
TOP: Standard Molar Enthalpies of Formation,...
18. ANS: B
TOP: Bond Energies
19. ANS: D
TOP: Changes in Internal Energy, Delta E
20. ANS: C
TOP: Relationship Between Delta H and Delta E
21. ANS: E
TOP: Changes in Internal Energy, Delta E
22. ANS: B
TOP: Relationship Between Delta H and Delta E