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)