18) The value of ΔS° for the decomposition of phosphorous trichloride into its constituent elements,
2PCl3 (g) → P2 (g) + 3Cl2( g)
is __________ J/K∙ mol.
A) -311.7
B) +311.7
C) +263.6
D) +129.4
E) -129.4
19) The value of ΔS° for the formation of calcium chloride from its constituent elements,
Ca (s) + Cl2 (g) → CaCl2 (s)
is __________ J/K∙ mol.
A) -104.6
B) +104.6
C) +369.0
D) -159.8
E) +159.8
20) The value of ΔS° for the decomposition of calcium chloride into its constituent elements,
CaCl2 (s) → Ca (s) + Cl2 (g)
is __________ J/K∙ mol.
A) -104.6
B) +104.6
C) +369.0
D) -159.8
E) +159.8
21) The value of ΔH° for the oxidation of solid elemental sulfur to gaseous sulfur trioxide,
2S (s, rhombic) + 3O2( g) → 2SO3 (g)
is __________ kJ/mol.
A) +790.4
B) -790.4
C) +395.2
D) -395.2
E) +105.1
22) The value of ΔH° for the decomposition of gaseous sulfur trioxide to its component elements,
2SO3 (g) → 2S (s, rhombic) + 3O2 (g)
is __________ kJ/mol.
A) +790.4
B) -790.4
C) +395.2
D) -395.2
E) +105.1
23) The value of ΔH° for the oxidation of solid elemental sulfur to gaseous sulfur dioxide,
S (s, rhombic) + O2 (g) → SO2 (g)
is __________ kJ/mol.
A) +269.9
B) -269.9
C) +0.00
D) -11.6
E) +11.6
24) The value of ΔH° for the decomposition of gaseous sulfur dioxide to solid elemental sulfur and
gaseous oxygen,
SO2 (g) → S (s,rhombic) + O2 (g)
is __________ kJ/mol.
A) +0.0
B) +135.0
C) -135.90
D) -269.9
E) +269.9
25) The value of ΔH° for the formation of POCl3 from its constituent elements,
P2 (g) + O2 (g) + 3Cl2 (g) → 2POCl3 (g)
is __________ kJ/mol.
A) -1228.7
B) -397.7
C) -686.5
D) +1228.7
E) +686.5
26) The value of ΔH° for the decomposition of POCl3 into its constituent elements,
2POCl3 (g) → P2 (g) + O2 (g) + 3Cl2 (g)
is __________ kJ/mol.
A) -1228.7
B) +1228.7
C) -940.1
D) +940.1
E) +0.00
27) The value of ΔH° for the formation of phosphorous trichloride from its constituent elements,
P2 (g) + 3Cl2 (g) → 2PCl3 (g)
is __________ kJ/mol
A) -288.1
B) +432.4
C) -720.5
D) +720.5
E) -432.4
28) The value of ΔH° for the decomposition of phosphorous trichloride into its constituent elements,
2PCl3 (g) → P2 (g) + 3Cl2 (g)
is __________ kJ/mol.
A) +576.2
B) -288.1
C) +720.5
D) +288.1
E) -720.5
29) The value of ΔH° for the formation of calcium chloride from its constituent elements,
Ca (s) + Cl2 (g) → CaCl2 (s)
is __________ kJ/mol.
A) +0.00
B) -397.9
C) +397.9
D) -795.8
E) +795.8
30) The value of ΔH° for the decomposition of calcium chloride into its constituent elements,
CaCl2 (s) → Ca (s) + Cl2 (g)
is __________ kJ/mol.
A) -0.00
B) -397.9
C) +397.9
D) -795.8
E) +795.8
31) The value of ΔG° at 25 °C for the oxidation of solid elemental sulfur to gaseous sulfur trioxide,
2S (s, rhombic) + 3O2 (g) → 2SO3 (g)
is __________ kJ/mol.
A) +740.8
B) -370.4
C) +370.4
D) -740.8
E) +185.2
32) The value of ΔG° at 25 °C for the oxidation of solid elemental sulfur to gaseous sulfur dioxide,
S (s, rhombic) + O2(g) → SO2 (g)
is __________ kJ/mol.
A) +395.2
B) +269.9
C) -269.9
D) +300.4
E) -300.4
33) The value of ΔG° at 25°C for the decomposition of gaseous sulfur trioxide to solid elemental sulfur
and gaseous oxygen,
2SO3 (g) → 2S (s, rhombic) + 3O2 (g)
is __________ kJ/mol.
A) +740.8
B) -370.4
C) +370.4
D) -740.8
E) +185.2
34) The value of ΔG° at 25°C for the decomposition of gaseous sulfur dioxide to solid elemental sulfur
and gaseous oxygen,
SO2 (g) → S (s, rhombic) + O2 (g)
is __________ kJ/mol.
A) +395.2
B) +269.9
C) -269.9
D) +300.4
E) -300.4
35) The value of ΔG° at 25°C for the formation of POCl3 from its constituent elements,
P2 (g) + O2 (g) + 3Cl2 (g) → 2POCl3 (g)
is __________ kJ/mol.
A) -1108.7
B) +1108.7
C) -606.2
D) +606.2
E) -1,005
36) The value of ΔG° at 25°C for the decomposition of POCl3 into its constituent elements,
2POCl3 (g) → P2 (g) + O2 (g) + 3Cl2 (g)
is __________ kJ/mol.
A) -1108.7
B) +1108.7
C) -606.2
D) +606.2
E) -1,005
37) The value of ΔG° at 25°C for the formation of phosphorous trichloride from its constituent elements,
P2 (g) + 3Cl2 (g) → 2PCl3 (g)
is __________ kJ/mol.
A) -539.2
B) +539.2
C) -642.9
D) +642.9
E) -373.3
38) The value of ΔG° at 25°C for the decomposition of phosphorous trichloride into its constituent
elements,
2PCl3 (g) → P2 (g) + 3Cl2 (g)
is __________ kJ/mol.
A) -539.2
B) +539.2
C) -642.9
D) +642.9
E) -373.3
39) The value of ΔG° at 25°C for the formation of calcium chloride from its constituent elements,
Ca (s) + Cl2 (g) → CaCl2 (s)
is __________ kJ/mol.
A) -795.8
B) +795.8
C) +763.7
D) +748.1
E) -748.1
40) The value of ΔG° at 25°C for the decomposition of calcium chloride into its constituent elements,
CaCl2 (s) → Ca (s) + Cl2 (g)
is __________ kJ/mol.
A) -795.8
B) +795.8
C) +763.7
D) +748.1
E) -748.1
41) The value of ΔG° at 373 K for the oxidation of solid elemental sulfur to gaseous sulfur dioxide,
S (s, rhombic) + O2 (g) → SO2 (g)
is __________ kJ/mol. At 298 K, ΔH° for this reaction is -269.9 kJ/mol, and ΔS° is +11.6 J/K.
A) -300.4
B) +300.4
C) -4,597
D) +4,597
E) -274.2
42) The value of ΔG° at 25°C for the following reaction:
C2H4 (g) + H2 (g) → C2H6 (g)
is __________ kJ/mol. At 298 K, ΔH° for this reaction is –137.5 kJ/mol, and ΔS° is +120.5 J/K.
A) -35800
B) -173.4
C) 35800
D) -101.7
E) -274.2
43) Given the thermodynamic data in the table below, calculate the equilibrium constant (at 298 K) for
the reaction:
2SO2 (g) + O2 (g) 2SO3 (g)
A) 2.37 × 1024
B) 1.06
C) 1.95
D) 3.82 × 1023
E) More data are needed.
44) The value of ΔG° for a reaction conducted at 25°C is 3.05 kJ/mol. The equilibrium constant for a
reaction is __________ at this temperature?
A) 0.292
B) -4.20
C) 0.320
D) -1.13
E) More information is needed.
45) The value of ΔG° for a reaction conducted at 25°C is 2.8 kJ/mol. The equilibrium constant for a
reaction is __________ at this temperature?
A) 1.13
B) -4.2
C) 0.32
D) -1.13
E) More information is needed.
46) Consider the reaction:
NH3 (g) + HCl (g) → NHO4Cl (s)
Given the following table of thermodynamic data at 298 K:
The value of K for the reaction at 25°C is __________.
A) 150
B) 9.2 × 1015
C) 8.4 × 104
D) 1.1 × 10-16
E) 1.4 × 108
47) Consider the reaction:
FeO (s) + Fe (s) + O2 (g) → Fe2O3 (s)
Given the following table of thermodynamic data at 298 K:
The value K for the reaction at 25°C is __________.
A) 370
B) 5.9 × 104
C) 3.8 × 10-14
D) 7.1 × 1085
E) 8.1 × 1019
48) Consider the reaction:
Ag+ (aq) + Cl– (aq) → AgCl (s)
Given the following table of thermodynamic data at 298 K:
The value of K for the reaction at 25°C is __________.
A) 810
B) 5.3 × 109
C) 1.8 × 104
D) 3.7 × 1010
E) 1.9 × 10-10
19.3 Algorithmic Questions
1) The normal boiling point of methanol is 64.7°C and the molar enthalpy of vaporization if 71.8
kJ/mol. The value of ΔS when 2.15 mol of CH3OH (l) vaporizes at 64.7°C is __________ J/K.
A) 0.457
B) 5.21 × 107
C) 457
D) 2.39 × 103
E) 2.39
2) 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) -88.8
C) -238
D) 373
E) -40.7
3) The normal boiling point of C2Cl3F3 is 47.6°C and its molar enthalpy of vaporization is 27.49
kJ/mol. What is the change in entropy in the system in J/K when 24.1 grams of C2Cl3F3 vaporizes to a
gas at the normal boiling point?
A) -11.0
B) -4.19
C) 4.19
D) 11.0
E) 27.5
4) The normal boiling point of ethanol (C2H5OH) is 78.3°C and its molar enthalpy of vaporization is
38.56 kJ/mol. What is the change in entropy in the system in J/K when 97.2 grams of ethanol at 1 atm
condenses to a liquid at the normal boiling point?
A) 330
B) 1038
C) -330
D) -1038
E) -231
5) The standard Gibbs free energy of formation of __________ is zero.
(a) H2O (l)
(b) O (g)
(c) I2 (s)
A) (a) only
B) (b) only
C) (c) only
D) (b) and (c)
E) (a), (b), and (c)
6) The standard Gibbs free energy of formation of __________ is zero.
(a) H2O (l)
(b) Mg (s)
(c) Br2 (l)
A) (a) only
B) (b) only
C) (c) only
D) (b) and (c)
E) (a), (b), and (c)
7) The standard Gibbs free energy of formation of __________ is zero.
(a) Si (s)
(b) F2 (g)
(c) Ni (s)
A) (a) only
B) (b) only
C) (c) only
D) (b) and (c)
E) (a), (b), and (c)
8) 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) -612.3
B) 3.65 × 104
C) 1.08 × 105
D) -683.3
E) -829.7
9) The value of ΔG° at 100.0°C for the formation of calcium chloride from its constituent elements:
Ca (s) + Cl2 (g) → CaCl2 (s)
is __________ kJ/mol. At 25.0°C for this reaction, ΔH° is –795.8 kJ/mol, ΔG° is –748.1 kJ/mol, and ΔS°
is -159.8 J/K.
A) -855.4
B) -736.1
C) 5.88 × 104
D) -779.8
E) 1.52 × 104
10) For the reaction
C(s) + H2O(g) → CO(g) + H2(g)
ΔH° = 131.3 kJ/mol and ΔS° = 127.6 J/K ∙ mol at 298 K. At temperatures greater than __________°C
this reaction is spontaneous under standard conditions.
A) 273
B) 325
C) 552
D) 756
E) 1029
11) For a given reaction, ΔH = –19.9 kJ/mol and ΔS = -55.5 J/K-mol. The reaction will have ΔG = 0 at
__________ K. Assume that ΔH and ΔS do not vary with temperature.
A) 359
B) 2789
C) 298
D) 2.79
E) 0.359
12) For a given reaction, ΔH = +35.5 kJ/mol and ΔS = +83.6 J/K-mol. The reaction is spontaneous
__________. Assume that ΔH and ΔS do not vary with temperature.
A) at T < 425 K
B) at T > 425 K
C) at all temperatures
D) at T > 298 K
E) at T < 298 K
13) In the Haber process, ammonia is synthesized from nitrogen and hydrogen:
N2 (g) + 3H2 (g) → 2NH3 (g)
ΔG° at 298 K for this reaction is –33.3 kJ/mol. The value of ΔG at 298 K for a reaction mixture that
consists of 1.9 atm N2, 1.6 atm H2, and 0.65 atm NH3 is __________.
A) -1.8
B) -3.86 × 103
C) -7.25 × 103
D) -104.5
E) -40.5
14) Phosphorous and chlorine gases combine to produce phosphorous trichloride:
P2 (g) + 3Cl2 (g) → 2PCl3 (g)
ΔG° at 298 K for this reaction is –642.9 kJ/mol. The value of ΔG at 298 K for a reaction mixture that
consists of 1.5 atm P2, 1.6 atm Cl2, and 0.65 atm PCl3 is __________.
A) -44.2
B) -3.88 × 103
C) -7.28 × 103
D) -708.4
E) -649.5
15) The equilibrium constant for a reaction is 0.35 at 25°C. What is the value of ΔG° (kJ/mol) at this
temperature?
A) 2.6
B) -4.2
C) 220
D) 4.2
E) More information is needed.
16) The equilibrium constant for the following reaction is 3.5 × 108 at 25°C.
N2 (g) + 3H2 (g) 2NH3 (g)
The value of ΔG° for this reaction is __________ kJ/mol.
A) 22
B) -4.1
C) 4.1
D) -49
E) -22
19.4 Short Answer Questions
1) A reversible change produces the maximum amount of ________ that can be achieved by the system
on the surroundings.
2) Calculate ΔG° (in kJ/mol) for the following reaction at 1 atm and 25°C:
C2H6 (g) + O2 (g) → CO2 (g) + H2O (l) (unbalanced)
ΔGf° C2H6 (g) = –32.89 kJ/mol; ΔGf° CO2 (g) = –394.4 kJ/mol; ΔGf° H2O (l) = -237.13 kJ/mol
3) Calculate ΔG° (in kJ/mol) for the following reaction at 1 atm and 25°C:
C2H6 (g) + O2 (g) → CO2 (g) + H2O (l) (unbalanced)
ΔHf° C2H6 (g) = -84.7 kJ/mol; S∘C2H6 (g) = 229.5 J/K ∙ mol;
ΔHf° CO2 (g) = -393.5 kJ/mol; S∘CO2 (g) = 213.6 J/K ∙ mol;
ΔHf° H2O (l) = -285.8 kJ/mol; S∘H2O (l) = 69.9 J/K ∙ mol;
S∘O2 (g) = 205.0 J/K ∙ mol
4) Find the temperature (in K) above which a reaction with a ΔH of 123.0 kJ/mol and a ΔS of 90.00 J/K∙
mol becomes spontaneous.
5) Find the temperature (in K) above which a reaction with a ΔH of 53.00 kJ/mol and a ΔS of 100.0 J/K∙
mol becomes spontaneous.
6) Calculate ΔG° for the autoionization of water at 25°C. Kw = 1.0 × 10–14
19.5 True/False Questions
1) The melting of a substance at its melting point is an isothermal process.
2) The vaporization of a substance at its boiling point is an isothermal process
3) The quantity of energy gained by a system equals the quantity of energy gained by its surroundings.
4) The entropy of a pure crystalline substance at 0°C is zero.
5) The more negative ΔG° is for a given reaction, the larger the value of the corresponding equilibrium
constant, K.