Post on 09-Feb-2018
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,
P2 (g) + 3Cl2 (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
1)
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:
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
3)
4) ΔS is negative for the reaction __________.
A) H2O (l) → H2O (g)
B) 2SO2 (g) + O2 (g) → 2SO3 (g)
C) NH4Cl (s) → NH3 (g) + HCl (g)
D) 2C (s) + O2 (g) → 2CO2 (g)
E) PbCl2 (s) → Pb2+ (aq) + 2Cl- (aq)
4)
5) The standard emf for the cell using the overall cell reaction below is +2.20 V:
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
5)
6) Which substance is the reducing agent in the reaction below?
Pb + PbO2 + 2H2SO4 → 2PbSO4 + 2H2O
A) H2SO4 B) PbO2 C) Pb D) H2O E) PbSO4
6)
7) __________ is the oxidizing agent in the reaction below.
Cr2O72- + 6S2O3
2- + 14H+ → 2Cr3+ + 3S4O62- + 7H2O
A) S2O32- B) S4O6
2- C) H+ D) Cr3+ E) Cr2O72-
7)
8) The equilibrium constant for the following reaction is 5.0 × 108 at 25°C.
N2 (g) + 3H2 (g) 2NH3 (g)
The value of ΔG° for this reaction is __________ kJ/mol.
A) -50 B) -25 C) -4.2 D) 22 E) -22
8)
9) Given the thermodynamic data in the table below, calculate the equilibrium constant (at 298 K) for
the reaction:
2 SO2 (g) + O2 (g) 2 SO3 (g)
Substance ΔHf° (kJ/mol) S° (J/mol · K)
SO2 (g) -297 249
O2 (g) 0 205
SO3 (g) -395 256
A) 2.37 × 1024
B) 3.82 × 1023
C) 1.95
D) 1.06
E) More data are needed.
9)
10) The standard cell potential (E°cell) for the reaction below is +0.63 V. The cell potential for this
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 B) 0.63 C) 0.41 D) 0.52 E) 0.74
10)
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)
(pg. 2)
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) ΔG°f (kJ/mol) S (J/K-mol)
Carbon
C (s, diamond) 1.88 2.84 2.43
C (s, graphite) 0 0 5.69
C2H2 (g) 226.7 209.2 200.8
C2H4 (g) 52.30 68.11 219.4
C2H6 (g) -84.68 -32.89 229.5
CO (g) -110.5 -137.2 197.9
CO2 (g) -393.5 -394.4 213.6
Hydrogen
H2( g) 0 0 130.58
Oxygen
O2 (g) 0 0 205.0
H2O (l) -285.83 -237.13 69.91
13) The combustion of ethene in the presence of excess oxygen yields carbon dioxide and water:
C2H4 (g) + 3O2 (g) → 2CO2 (g) + 2H2O (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
13)
14) The value of ΔS° for the reaction
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
14)
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
15)
(pg. 3)
16) Consider the reaction:
Ag+ (aq) + Cl- (aq) → AgCl (s)
Given the following table of thermodynamic data at 298 K:
Substance ΔHf° (kJ/mol) S° (J/K· mol)
Ag+ (aq) 105.90 73.93
Cl- (aq) -167.2 56.5
AgCl(s) -127.0 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
16)
17) What is the coefficient of the dichromate ion when the following equation is balanced?
Fe2+ + Cr2O72- → Fe3+ + Cr3+ (acidic solution)
A) 6 B) 3 C) 1 D) 2 E) 5
17)
18) What is the coefficient of Fe3+ when the following equation is balanced?
CN- + Fe3+ → CNO- + Fe2+ (basic solution)
A) 1 B) 2 C) 3 D) 4 E) 5
18)
(pg. 4)
Answer KeyTestname: 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
(pg. 5)