Thermodynamics Test Study Guide—AP
_____ 1. The entropy change (ΔS) is positive for which of the following reactions?
I.
II.
III.
a)
b)
c)
d)
e)
H2O (g)  H2O (l)
O2 (g)  O2 (aq)
Br2 (l)  Br2 (g)
I only
I and II only
II and III only
III only
I, II, and III
_____ 2. When KNO3 dissolves in water the temperature of the solution decreases. What
are the correct signs for the ΔH, ΔS, and ΔG for this process?
ΔH
ΔS
ΔG
a)
b)
c)
d)
e)
+
+
+
+
+
+
+
+
+
+
_____ 3. Which of the following statements is true if ΔG is positive is positive for a
certain process?
I.
The reaction is spontaneous at that temperature.
II.
The reaction is endothermic.
III.
The reaction is non-spontaneous at that temperature.
IV.
The reaction is exothermic.
a)
b)
c)
d)
e)
I only
I and II only
III only
III and IV only
I and IV only
_____ 4. It is found that a certain process is spontaneous at a temperature of 278K, but is
non-spontaneous at 398K. Which of the following statements are true when the system
is at 278K?
a)
b)
c)
d)
e)
ΔS and ΔH are positive, and ΔG is negative
ΔS, ΔH, and ΔG are negative
ΔS and ΔH are negative, and ΔG is positive
ΔG and ΔH are negative, and ΔS is positive
ΔS, ΔH, and ΔG are positive
_____ 5. 2CO (g)  O2 (g) + 2C (s) ΔH = +220 kJ/mol
2CO (g) + O2 (g)  2CO2 (g) ΔH = -566 kJ/mol
Use the information above to find the enthalpy change for the following reaction:
2C(s) + 2O2  2CO2
a)
b)
c)
d)
e)
-346 kJ/mol
+346 kJ/mol
+786 kJ/mol
-786 kJ/mol
-393 kJ/mol
_____ 6. Find the enthalpy change, ΔH, for the following reaction using the information
in the table below.
H2 + F2  2HF
Bond
H--H
F—F
H—F
Average Bond Energy (kJ/mol)
432
154
565
a)
b)
c)
d)
e)
-544 kJ/mol
+544 kJ/mol
+21 kJ/mol
-21 kJ/mol
+1151 kJ/mol
2007 Free Response A
7. N2 (g) + 3F2 (g)  2NF3 (g) ΔH298 = -264 kJ/mol ΔS298 = -278 J/Kmol
The following questions are related to the synthesis reaction represented by the chemical
equation above
a) calculate the value of the standard free energy change (ΔG298) for the
reaction.
b) Determine the temperature at which the equilibrium constant (Keq) for the
reaction is equal to 1.00. ( Assume the ΔH and the ΔS are independent of
temperature).
c) Calculate the standard enthalpy change (ΔH) that occurs when 0.256 mol of
NF3 (g) is formed from N2 (g) and F2 (g) at 1.00 atm and 298K.
d) The enthalpy change in a chemical reaction is the difference between energy
absorbed in breaking bonds in the reactants and energy released by bond
formation in the products. How many bonds are formed when two molecules
of NF3 are produced according to the equation?
e) Use both the information in the equation above and the table of average bond
enthalpies below to calculate the average enthalpy in the F—F bond.
Bond
N—N
N—F
F—F
Average Bond Enthalpy
(kJ/mol)
946
272
?
8. Parts (a) through (c) pertain to the following process.
2C4H10 (g) + 13O2 (g)  8CO2 (g) + 10H2O (g)
a) Find the standard enthalpy change, ΔH, for the reaction above using the
information given in the following table.
4C(graphite) + 5H2  C4H10 (g)
C(graphite) + O2  CO2 (g)
2H2 (g) + O2 (g)  2H2O (g)
Standard Enthalpy Change (ΔH), kJ/mol
-124.73
-393.50
-483.64
b) Predict the sign for the entropy change, ΔS, in this reaction. Justify your answer.
c) Predict the sign for the free energy change, ΔG, in this reaction. Justify your
answer.
9. A 200.0-gram metal bar requires 1.200 kcal to change its temperature from 0.0oC to
100.0oC. What is the specific heat of the metal, in J/g-oC?
10. A student adds 200.0 grams of copper metal shot at 25.0oC to 200.0 mL of water at
80.0oC. The final temperature of the mixture is 75.3oC. Assuming that the specific
heat of water is 1.00 cal/g-oC and that no heat is lost to or gained from the
surroundings, what is the specific heat of copper, in cal/g-oC?
11. The combustion of 0.100 gram of ethane causes a temperature rise of 2.00oC in a
bomb calorimeter that has a heat capacity of 2.510 kJ/oC. What is the internal
energy change, per mole, of ethane for the combustion reaction?
______12. It is found that Go = -394 kJ/mole at a given temperature for the reaction:
C(s) + O2(g)  CO2(g)
At this temperature, which statement is TRUE for the reaction?
A) The system is at equilibrium.
B) The process, as written, is not possible.
C) Gaseous carbon dioxide will be formed spontaneously.
D) Gaseous carbon dioxide will decompose spontaneously.
E) The process will proceed very rapidly.
_____13. For which of the following reaction systems would Ssystem < 0?
A) 2 H2O(g)  2 H2(g) + O2(g) ; B) CH4(g) + 2 O2(g)  C O2(g) + 2 H2O(g)
C) CH4(g) + 2 O2(g)  CO2(g) + 2 H2O(liq);
2 H2O(liq)
D) CH4(g) + 3/2 O2(g)  CO(g) +
_____ 14. Which of the following statements is FALSE?
A) For an irreversible process, entropy is not conserved.
B) PV can have
units of joules.
C) The enthalpy of a perfect crystal at 0 K is zero. D) Energy can be transferred
as heat or work.
E) For reactions involving no gases, H is approximately equal to E.
_____ 15. Which of the following is the standard formation reaction for NH4Br(s) at
o
25 C?
A)
B)
C)
D)
E)
1/2 N2(g) + 2 H2(g) + 1/2 Br2(g) --------> NH4Br(s)
NH3(g) + HBr(g) ------------> NH4Br(s)
NH3(aq) + HBr(aq) ------------> NH4Br(s)
1/2 N2(g) + 2 H2(g) + 1/2 Br2(liq) --------> NH4Br(s)
1/2 N2(g) + 2 H2(g) + 1/2 Br2(s) --------> NH4Br(s)
o
______ 16. Given the reaction below, with thermodynamic values (25 C) tabulated
beneath each species, what is the standard free energy change for this reaction at
298 K?
C3H8(g) -------->
CH4(g)
+
C2H4(g)
o
H f
o
S
A) -9644 kcal;
+9644 kcal.
-24.82
+64.51
B) -9.77 kcal;
-17.88
+44.49
C) +9.77 kcal;
+12.49
+52.45
kcal/mole
.
cal/mole K
D) +19.42 kcal;
______ 17. Which of the following must be true for a spontaneous process?
A) H < 0;
B) Stotal > 0;
C) G > 0;
D)  Ssystem > 0;
TSsystem < H.
E)
E)
_____ 18. Which of the following statements is FALSE?
A) According to the third law of thermodynamics, S = 0 for a perfect crystal at
o
0 C.
B) According to the first law of thermodynamics, energy is conserved.
C) According to the second law of thermodynamics, the total energy change is
positive for a spontaneous process.
D) PV has the units of energy.
E) For reactions involving only condensed phases, H is approximately equal to
E.