AP Chemistry - Unit 9 Practice Test (Thermochemistry and Electrochemistry -
Chapters 19 and 20). 1) The value of ΔG° at 141.0 °C for the formation of ...
AP Chemistry - Unit 9 Practice Test (Thermochemistry and Electrochemistry - Chapters 19 and 20) 1) The value of ΔG° at 141.0 °C for the formation of phosphorous trichloride from its constituent elements,
1)
P2 (g) + 3Cl 2 (g) → 2PCl3 (g) is __________ kJ/mol. At 25.0°C for this reaction, ΔH° is -720.5 kJ/mol, ΔG° is -642.9 kJ/mol, and ΔS° is -263.7 J/K. A) -683.3 B) 3.65 × 104 C) -829.7 D) -612.3 E) 1.08 × 105 2) How many grams of copper will be plated out by a current of 2.3 A applied for 25 minutes to a 0.50 M solution of copper(II) sulfate? A) 1.8 × 10-2 B) 2.2 C) 0.019 D) 0.036 E) 1.1
2)
3) The standard cell potential (E°) of a voltaic cell constructed using the cell reaction below is 0.76 V:
3)
Zn (s) + 2H+ (aq) → Zn2+ (aq) + H2 (g) With PH2 = 1.0 atm and [Zn2+ ] = 1.0 M, the cell potential is 0.66 V. The concentration of H+ in the cathode compartment is __________ M. A) 1.4 × 10-1 B) 4.9 × 101 C) 4.2 × 10-4 D) 1.0 × 10-12 E) 2.0 × 10-2 4) ΔS is negative for the reaction __________. A) H2 O (l) → H2 O (g)
4)
B) 2SO2 (g) + O2 (g) → 2SO3 (g) C) NH4 Cl (s) → NH3 (g) + HCl (g) D) 2C (s) + O2 (g) → 2CO2 (g) E) PbCl2 (s) → Pb2+ (aq) + 2Cl- (aq) 5) The standard emf for the cell using the overall cell reaction below is +2.20 V:
5)
2Al (s) + 3I2 (s) → 2Al3+ (aq) + 6I- (aq) The emf generated by the cell when [Al3+ ] = 4.5 × 10-3 M and [I-] = 0.15 M is ________ V. A) 2.23 B) 2.32 C) 2.20 D) 2.10 E) 2.39 6) Which substance is the reducing agent in the reaction below?
6)
Pb + PbO2 + 2H2 SO4 → 2PbSO4 + 2H2 O A) H2 SO4
B) PbO2
C) Pb
D) H2 O
E) PbSO4
7) __________ is the oxidizing agent in the reaction below.
A) 2.37 × 1024 B) 3.82 × 1023 C) 1.95 D) 1.06 E) More data are needed. 10) The standard cell potential (E°cell ) for the reaction below is +0.63 V. The cell potential for this
10)
reaction is __________ V when [ Zn2+ ] = 1.0 M and [Pb2+ ] = 2.0 × 10-4 M. Pb2+ (aq) + Zn (s) → Zn2+ (aq) + Pb (s) A) 0.85
(pg. 2)
B) 0.63
C) 0.41
D) 0.52
E) 0.74
11) The normal boiling point of water is 100.0°C and its molar enthalpy of vaporization is 40.67 kJ/mol. What is the change in entropy in the system in J/K when 39.3 grams of steam at 1 atm condenses to a liquid at the normal boiling point? A) -88.8 B) -40.7 C) 373 D) 88.8 E) -238
11)
12) For a reaction to be spontaneous under standard conditions at all temperatures, the signs of ΔH° and ΔS° must be __________ and __________, respectively. A) +, + B) +, C) -, + D) -, E) +, 0
12)
Use the table below to answer the questions that follow. Thermodynamic Quantities for Selected Substances at 298.15 K (25°C) Substance
ΔH°f (kJ/mol)
Carbon C (s, diamond) C (s, graphite) C2 H2 (g) C2 H4 (g) C2 H6 (g) CO (g) CO2 (g)
ΔG°f (kJ/mol)
S (J/K-mol)
1.88 0 226.7
2.84 0 209.2
2.43 5.69 200.8
52.30
68.11
219.4
-32.89
229.5
-84.68 -110.5 -393.5
197.9 213.6
-137.2 -394.4
Hydrogen H2 ( g)
0
0
130.58
Oxygen O2 (g)
0
0
205.0
-285.83
-237.13
H2 O (l)
69.91
13) The combustion of ethene in the presence of excess oxygen yields carbon dioxide and water:
13)
C2 H4 (g) + 3O2 (g) → 2CO2 (g) + 2H2 O (l) The value of ΔS° for this reaction is __________ J/K· mol. A) -267.4 B) +347.6 C) -140.9
D) -347.6
E) +140.9
14) The value of ΔS° for the reaction
14)
2C (s, diamond) + O2 (g) → 2CO (g) is __________ J/K· mol. A) -195.7 B) +185.9
C) +9.5
D) -9.5
E) -185.9
15) How many minutes will it take to plate out 4.56 g of Ni metal from a solution of Ni+2 using a current of 45.5 amps in an electrolytic cell? A) 2.75 B) 4.55 C) 330 D) 5.49 E) 155
(pg. 3)
15)
16) Consider the reaction:
16)
Ag+ (aq) + Cl- (aq) → AgCl (s) Given the following table of thermodynamic data at 298 K: Substance Ag+ (aq) Cl- (aq) AgCl(s)
ΔHf° (kJ/mol)
S° (J/K· mol)
105.90
73.93
-167.2 -127.0
56.5 96.11
The value of K for the reaction at 25°C is __________. A) 810 B) 1.8 × 104 C) 3.7 × 1010 D) 5.3 × 109 E) 1.9 × 10-10 17) What is the coefficient of the dichromate ion when the following equation is balanced? Fe2+ + Cr2 O7 2- → Fe3+ + Cr3+ A) 6
B) 3
(acidic solution) C) 1
D) 2
E) 5
18) What is the coefficient of Fe3+ when the following equation is balanced? CN- + Fe3+ → CNO- + Fe2+ A) 1
(pg. 4)
B) 2
17)
18)
(basic solution) C) 3
D) 4
E) 5
Answer Key Testname: APCU9PRACTICE
1) D 2) E 3) E 4) B 5) B 6) C 7) E 8) A 9) A 10) D 11) E 12) C 13) A 14) B 15) D 16) D 17) C 18) B
