Chemistry 2
Practice Exam 4
Helpful Information: R = 8.314 J / (K • mol)
1. Which process has a positive S°?
I. 2 H2(g) + O2(g) 2 H2O(g)
II. Ag+(aq) + Cl-(aq) AgCl(s)
III. 2 KClO3(s) 2 KCl(s) + 3 O2(g)
a) I & II
b) I & III
c) II & III
d) I & II & III
e) III only
2. What is S° for the reaction below?
4Al(s) + 3 O2(g) 2 Al2O3(s)
Compound |
S°ac J/(K·mol) |
Al(s) |
- 136 |
Al2O3(s) |
- 761 |
O2(g) |
- 117 |
a) - 1014 J/(K·mol)
b) - 627 J/(K·mol)
c) - 508 J/(K·mol)
d) + 627 J/(K·mol)
e) + 2593 J/(K·mol)
3. What relationship correctly describes a reaction at equilibrium?
a) Q = 0
b) G = 0
c) G° = 0
d) ln K = 0
e) G° = G
4. The second law of thermodynamics relates Ssystem and Ssurroundings to the Suniverse. Natural processes are spontaneous if Suniverse is ...
a) decreasing.
b) increasing.
c) positive in sign.
d) negative in sign.
e) equal to the
5. What is the spontaneity of the two processes below at 25°C ?
I. CH3CH2OH(s) CH3CH2OH(l) mp = -177.3°C
II. CH3CH2OH(l) CH3CH2OH(g) bp = 78.5°C
a) Only I is spontaneous.
b) Only II is spontaneous.
c) I & II are both spontaneous.
d) I & II are both nonspontaneous.
e) More information must be given.
6. What factor(s) determine the direction in which a reaction is spontaneous?
a) Only Enthalpy
b) Enthalpy & Entropy
c) Entropy & Temperature
d) Enthalpy & Temperature
e) Enthalpy, Entropy, & Temperature
a) Both the disorder in the room and the children will increase.
b) Both the disorder in the room and the children will decrease.
c) The disorder in the room and the children will stay a about the same.
d) The disorder of the room will decrease & disorder of the children will increase.
e) The disorder of the room will increase & disorder of the children will decrease.
8. Determine what is the driving force for the reaction below.
2 NH4NO3(s) 2 N2(g) + O2(g) + 4 H2O(g)
Compound |
H°ac kJ/mol |
S°ac J / (K·mol) |
H2O(g) |
- 926 |
- 202 |
N2(g) |
- 945 |
- 115 |
NH4NO3(s) |
- 2929 |
- 1098 |
O2(g) |
- 498 |
- 117 |
a) Entropy only
b) Enthalpy only
c) Enthalpy and Entropy
d) Neither Enthaply nor Entropy
9. What is the equilibrium constant (K) for the reaction below at 600 K ?
2 CH4(g) C2H6(g) + H2(g) G°rxn = + 72.3 kJ/mol
a) 2.0
10. Calculate G°rxn for the reaction below using G°ac data.
2 CH3OH(g) + 3 O2(g) 2 CO2(g) + 4 H2O(g)
Compound |
G°ac kJ/mol |
CO2(g) |
- 1529 |
CH3OH(g) |
- 1878 |
H2O(g) |
- 867 |
O2(g) |
- 463 |
a) - 2777 kJ/mol
b) - 1381 kJ/mol
c) - 55 kJ/mol
d) + 4757 kJ/mol
e) + 11671 kJ/mol
11. The protein trypsin can be denatured by heat as in the reaction below. What is the maximum temperature at which trypsin is stable? (e.g. G = 0 and H° and S° do not change much with temperature).
trypsin denatured trypsin
H°rxn = + 278 kJ/mol S°rxn = + 876 J/(K·mol)
a) 0.317 K
b) 16.7 K
c) 94.6 K
d) 317 K
e) 3150K
12. What is G°rxn in kJ for the acid dissociation reaction of citric acid in H2O at 298 K if the
Ka = 7.5
H3Cit(aq) + H2O(l) H3O+(aq) + H2Cit-(aq)
a) + 1.3 kJ/mol
b) + 3.1 kJ/mol
c) + 10 kJ/mol
d) + 24 kJ/mol
e) + 126 kJ/mol
a) be spontaneous if H°rxn > T S°rxn.
b) be spontaneous if H°rxn < T S°rxn.
c) be spontaneous at all temperatures.
d) not be spontaneous at any temperature.
e) need more information to predict spontaneity.
14. For a particular reaction, G°rxn is - 150 kJ/mol. You can predict that
a) the reaction is very close to equilibrium.
b) the equilibrium constant, K, is very large.
c) the equilibrium constant, K, is very small.
d) there are no driving forces for this reaction.
e) the reaction is at equilbrium at standard conditions.
15. What is the partial pressure of NO2(g) at equilibrium, if initially 1.0 atm of N2O4 is allowed to decompose at - 78°C?
N2O4(g) 2 NO2(g) Kp = 4.0
´ 10-8a) 1.4
´ 10-4 atm
16. Which equation correctly describes the relationship between Kp and Kc for the reaction below?
4 NH3(g) + 3 O2(g) 2 N2(g) + 6 H2O(g)
a) Kp = Kc
b) Kp = Kc
17. Standard state conditions for H°, S°, and G° are
a) Partial Pressures = 1 torr , Concentrations = 1 M, and Temperature = 0 K
b) Partial Pressures = 1 atm , Concentrations = 1 M, and Temperature = 273 K
c) Partial Pressures = 1 atm , Concentrations = 1 M, and Temperature = 298 K
d) Partial Pressures = 1 torr , Concentrations = 1 ppm, and Temperature = 0 K
e) whatever conditions that will achieve equilibrium.
18. BONUS: A BaSO4 slurry is consumed before an x-ray of the gastrointestinal tract to make it show up better on the x-ray. If G° at 37°C (body temperature) is
59.1 kJ/mol, what is the concentration of Ba2+ in the intestinal tract?
BaSO4(s) Ba2+(aq) + SO42-(aq)
a) 9.9