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

Sac J/(Kmol)

Al(s)

- 136

Al2O3(s)

- 761

O2(g)

- 117

 

a)  - 1014 J/(Kmol)
b)  - 627 J/(Kmol)
c)  - 508 J/(Kmol)
d)  + 627 J/(Kmol)
e)  + 2593 J/(Kmol)
 

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
D Ssystem.

 

5. What is the spontaneity of the two processes below at 25C ?

I. CH3CH2OH(s) CH3CH2OH(l) mp = -177.3C

II. CH3CH2OH(l) CH3CH2OH(g) bp = 78.5C

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
 

  1. Two small active children enter a room and proceed to play for 1 hr. Predict what happens to the room (surroundings) and the children (system) during this time.

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

Hac kJ/mol

Sac J / (Kmol)

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)           Grxn = + 72.3 kJ/mol

a)  2.0 10+6
b)  0.99
c)  5.1
10-7
d)  2.1
10-13
e)  3.2
10-15

 

10. Calculate Grxn for the reaction below using Gac data.

2 CH3OH(g) + 3 O2(g) 2 CO2(g) + 4 H2O(g)

Compound

Gac 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
Hrxn = + 278 kJ/mol
          Srxn = + 876 J/(Kmol)

a)  0.317 K
b)  16.7 K
c)  94.6 K
d)  317 K
e)  3150K

 

12. What is Grxn in kJ for the acid dissociation reaction of citric acid in H2O at 298 K if the
Ka = 7.5
10-5 ?

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

 

  1. A reaction has a (-)Hrxn and (-)Srxn. This reaction will ...

a)  be spontaneous if Hrxn > T Srxn.
b)  be spontaneous if Hrxn < T Srxn.
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, Grxn 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 - 78C?

N2O4(g) 2 NO2(g)         Kp = 4.0 10-8

a)  1.4 10-4 atm
b)  2.0
10-4 atm
c)  2.8
10-4 atm
d)  1.0
10-6 atm
e)  4.0
10-8 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
(RT)
c)  Kp = Kc
(RT)-1
d)  Kp = Kc
(RT)7/8
e)  Kp = Kc
(RT)8/7

 

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 37C (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 10-1 M
b)   1.0
10-5 M
c)   1.1
10-10 M
d)   5.5
10-11 M
e)   3.5
10-12 M