1) Which of the following is probably true for
a solid solute with a highly endothermic
heat of solution when dissolved in water?
a.The solid has a low lattice energy.
b.As the solute dissolves, the temperature of
the solution increases.
c.The resulting solution is ideal.
d.The solid is more soluble at higher
temperatures.
e.The solid has a high energy of hydration.
D
2). Which of the following reactions has
the largest positive value of ΔS per mole
of Cl2.
a. H2(g) + Cl2(g) --> 2 HCl(g)
b. C12(g) + 2 O2(g) --> Cl2O(g)
c. Mg(s) + Cl2(g) --> MgCl2(s)
d. 2 NH4Cl(s) --> 4 H2(g) + Cl2(g)
e. Cl2(g) --> 2 Cl(g)
D
3). Which of the following must be true for
a reaction that proceeds spontaneously
from initial standard state conditions?
a. ΔG° > 0 and Keq > 1
b. ΔG° > 0 and Keq < 1
c. ΔG° < 0 and Keq > 1
d. ΔG° < 0 and Keq < 1
e. ΔG° = 0 and Keq = 1
• C
4) H2O(s) --> H2O(l)
When ice melts at its normal melting point,
273.16 K and 1 atmosphere, which of the
following is true for the process shown
above?
a. DH < 0, DS > 0, DV > 0
b. DH < 0, DS < 0, DV > 0
c. DH > 0, DS < 0, DV < 0
d. DH > 0, DS > 0, DV >0
e. DH > 0, DS > 0, DV < 0
E
5) CH4(g) + 2 O2(g) --> CO2(g) + 2 H2O(l)
ΔHf°CH4
= –889.1 kJ
ΔHf°H2O(l) = –285.8 kJ/mol
ΔHf°CO2(g) = –393.3 kJ/mol
What is the standard heat of formation of
methane, ΔHf°CH4(g), as calculated from
the data above?
(A) –210.0 kJ/mole (D) 75.8 kJ/mole
(B) –107.5 kJ/mole (E) 210.0 kJ/mole
(C) –75.8 kJ/mole
c
ΔH° = –286 kJ
2 Na(s) + 1/2 O2(g) --> Na2O(s) ΔH°= –414 kJ
Na(s) + 1/2 O2(g) + 1/2 H2(g) --> NaOH(s) ΔH°= –
425 kJ
6) H2(g) + 1/2 O2(g) --> H2O(l)
Based on the information above, what is the
standard enthalpy change for the following
reaction?
Na2O(s) + H2O(l) --> 2 NaOH(s)
A) –1,125 kJ (B) –978 kJ
(C) –722 kJ (D) –150 kJ
(E) +275 kJ
• D
7) For which of the following processes
would ΔS have a negative value?
I. 2 Fe2O3(s) --> 4 Fe(s) + 3 O2(g)
II.Mg2+ + 2 OH– --> Mg(OH)2(s)
III. H2(g) + C2H4(g) --> C2H6(g)
(A) I only
(B) I and II only
(C) I and III only (D) II and III only
(E) I, II, and III
• D
8)
N2(g) + 3 H2(g) --> 2 NH3(g)
The reaction indicated above is
thermodynamically spontaneous at 298 K, but
becomes nonspontaneous at higher
temperatures. Which of the following is true at
298 K?
(A) ΔG, ΔH, and ΔS are all positive.
(B) ΔG, ΔH. and ΔS are all negative.
(C) ΔG and ΔH are negative, but ΔS is positive.
(D) ΔG and ΔS are negative, but ΔH is positive.
(E) ΔG and ΔH are positive, but ΔS is negative.
• B
1997 D
For the gaseous equilibrium represented below, it is
observed that greater amounts of PCl3 and Cl2 are
produced as the temperature is increased.
PCl5(g) ® PCl3(g) + Cl2(g)
(a)
What is the sign of DS° for the reaction? Explain.
(b)
What change, if any, will occur in DG° for the
reaction as the temperature is increased? Explain your
reasoning in terms of thermodynamic principles.
(c)
If He gas is added to the original reaction mixture at
constant volume and temperature, what will happen to
the partial pressure of Cl2? Explain.
(d)
If the volume of the reaction mixture is decreased at
constant temperature to half the original volume, what
will happen to the number of moles of Cl2 in the reaction
vessel? Explain.
1996 B
C2H2(g) + 2 H2(g)  C2H6(g)
Information about the substances involved in the reaction
represented above is summarized in the following tables.
Substance
C2H2(g)
H2(g)
C2H6(g)
S° (J/molK) DH°f (kJ/mol)
200.9
226.7
130.7
0
xx
-84.7
• (a) If the value of the standard entropy change, DS°, for
the reaction is -232.7 joules per moleKelvin, calculate
the standard molar entropy, S°, of C2H6 gas.
• (b) Calculate the value of the standard free-energy
change, DG°, for the reaction. What does the sign of
DG° indicate about the reaction above?
• (c) Calculate the value of the equilibrium constant, K,
for the reaction at 298 K.
(
1998 B
C6H5OH(s) + 7 O2(g)  6 CO2(g) + 3 H2O(l)
When a 2.000-gram sample of pure phenol, C6H5OH(s), is completely
burned according to the equation above, 64.98 kilojoules of heat is
released. Use the information in the table below to answer the
questions that follow.
Substance Standard Heat of Formation
Absolute Entropy
DH°C at 25°C (kJ/mol) ,
S°, at 25°C(J/mol K)
C(graphite)
0.00
5.69
CO2(g)
-393.5
213.6
H2(g)
0.00
130.6
H2O(l)
-285.85
69.91
O2(g)
0.00
205.0
C6H5OH(s)
?
144.0
• (a) Calculate the molar heat of combustion of phenol in kilojoules
per mole at 25°C.
• (b) Calculate the standard heat of formation, DH°, of phenol in
kilojoules per mole at 25°C.
• (c) Calculate the value of the standard free-energy change, DG°,
for the combustion of phenol at 25°C.
• (d) If the volume of the combustion container is 10.0 liters,
calculate the final pressure in the container when the temperature is
changed to 110.°C. (Assume no oxygen remains unreacted and that
all products are gaseous.)