DIRECTIONALITY THERMODYNAMICS: OF CHEMICAL REACTIONS
Chapter 17 Outline
Probs:
Sect.
16, 18, 21, 22, 24, 27, 30, 32, 36, 38, 52, 56
+ Supplementary Questions (attached)
Title and Comments
Required?
1.
Reactant-Favored and Product Favored Processes
YES
2.
Chemical Reactions and Dispersal of Energy
YES
3.
Measuring Dispersal of Energy: Entropy
YES
4.
Calculating Entropy Changes
YES
5.
Entropy and the Second Law of Thermodynamics
YES
6.
Gibbs Free Energy
YES
7.
Gibbs Free Energy Changes and Equilibrium Constants
YES
8.
Gibbs Free Energy and Maximum Work
NO
9.
Conservation of Gibbs Free Energy
NO
10.
Thermodynamic and Kinetic Stability
Note: I have added short discussions of various applications of G
in Biological/Biochemical Systems.
NOTE: You are encouraged to study the Sample Exercises in the sections.
Often in class, we will work alternative examples instead, in order to give you a
wider range of worked problems.
YES
CHAPTER 17
SUPPLEMENTARY HOMEWORK QUESTIONS
1. If a reaction is product-favored at any temperature, then Ho is
a. positive; positive
b. positive; negative
c. zero; positive
d. negative; positive
e. negative; negative
and So is
.
2. At constant T and P, in which of the following situations will the reaction never be product-favored?
a. H > 0 and S < 0
b. H > 0 and S > 0
c. H < 0 and S < 0
d. H < 0 and S > 0
e. none of the above
3. A reaction is exothermic and has a negative value of So. The value of Go for this reaction is
therefore:
a. negative at all temperatures.
b. positive at all temperatures.
c. positive above 0oC and negative below 0oC.
d. positive above a certain temperature and negative below it.
e. negative above a certain temperature and positive below it.
4. Use the data given to calculate the value of
Grxn for the reaction at 25C.
2 C(graphite) H2(g) + C2H2(g)
S (J K-1 mol-1)
Hf (kJ/mol)
C(graphite)
5.74
0
H2(g)
130.68
0
C2H2(g)
201.0
-226.8
a. -291.4 kJ
b. -244.3 kJ
c. -226.8 kJ
d.-207.6 kJ
e. -64.6 kJ
5. A certain reaction has Hrxn = +177.8 kJ, and Srxn = +160.5 J/K. Above what temperature does it
become product-favored ?
a. 384 C
b. 630 C
c. 835 C
d. 1108 C
e. 1381 C
6. What is the value of the equilibrium constant at 25oC for a reaction, if the value of Grxn is -47.8 kJ
at 25oC?
a. 1.70
b. 6.88
c. 2.30 x 102
d. 2.74 x 105
e. 2.37 108
7. Recovering aluminum directly from its ore, which is primarily aluminum oxide, involves the
following reaction, for which thermodynamic data is tabulated below:
2 Al2O3(s)
4 Al(s) + 3 O2(g)
aluminum
Hof (kJ/mole)
So (J K-1 mol-1)
aluminum oxide
-1676.0
oxygen
28.28
50.96
205.15
a. Calculate Horxn and Sorxn.
b. Explain how you could have predicted the signs of Horxn and Sorxn without any calculations.
c. Without performing any further calculations, predict whether this reaction will be product-favored
only above a certain temperature, or only below a certain temperature. Explain your answer.
d. Calculate the temperature alluded to in part c.
e. Calculate Go at this temperature.
8. For the reaction shown, G = -32.8 kJ at 25C.
N2(g) + 3H2(g) 2NH3(g)
a. Calculate the equilibrium constant for this reaction at 25oC.
b. Is a mixture of the three gases where pN2 = 3.5 bar, pH2 = 1.2 bar, and pNH3 = 0.22 bar at
equilibrium? Justify your answer.
c. What is the value of G under the conditions of part b?
d. Compare the answer from part c. with Go. Explain the difference observed.
9. For the reaction, CaCO3(s) CaO(s) + CO2(g), Ho = +178 kJ/mol and So = +161 J/mol-K.
a. What is the value of Go at 25 oC?
b. What is the value of Go at 1500 oC?
c. At what temperature, in oC, are the reactants and products in equilibrium? (i.e. Go = 0)