Dr. White
Chem 1B
Worksheet 16 Free Energy and the equilibrium
1. An equilibrium reaction was studied at various temperatures. The data was plotted and is
shown below:
a. If the equation for the line is y = 1.0x104x + 11.4, what is the ΔS° and the ΔH° for
the reaction?
b. When the temperature is decreased what happens to the value of K?
2. The thermodynamic equilibrium constant for the vaporization of water,
H2O(l) ⇄ H2O(g)
is Kp = PH2O. Over a wide range of temperatures, ΔH˚ = 44.0 kJ and ΔS˚ = 118.8 J/K.
(a) Calculate ΔG˚ at 45˚C
(b) Calculate K at 45˚C
(c) What is the vapor pressure of water at 45˚C?
(d) What is the value of K at 100.°C?
3. The Ksp of PbCl2 (s) is 1.7 x 10-5 at 25°C.
(a) What is ΔG°?
(b) Is it possible to prepare a solution that contains Pb2+ (aq) and Cl- (aq) at their
standard state concentrations?
1
Dr. White
Chem 1B
2
4. Consider the following gas phase reaction of A2 (clear) and B2 (filled) molecules:
A2 (g) + B2 (g)
2 AB (g)
ΔG˚ = 15 kJ
Which of the following reaction mixtures has the largest ΔG of reaction and which has
the smallest? Explain. (HINT: How is ΔG related to ΔG°?)
(1)
(2)
(3)
(b) If the partial pressure of each reactant and product in reaction mixture (1) is equal to
1 atm, what is the value of ΔG for the reaction in mixture (1)?
5. Sulfuric acid is produced in larger amounts than any other chemical. It is used in
manufacturing fertilizers, oil refining, and literally hundreds of other processes. An
intermediate step in the industrial process for synthesis of H2SO4 involves catalytic oxidation
of sulfur dioxide:
2SO2(g) + O2(g) --> 2SO3(g);
ΔG˚ = -141.8 kJ
Calculate ΔG at 25˚C given the following sets of partial pressures:
(a) 100 atm SO2, 100 atm O2, 1.0 atm SO3
(b) 2.0 atm SO2, 1.0 atm O2, 10 atm SO3
6. A BaSO4 slurry is ingested before the gastrointestinal tract is x-rayed because it is opaque
to x-rays and defines the contour of the tract. Ba2+ ion is toxic, but the compound is nearly
insoluble, If ΔG° at 37°C (body temperature) is 59.1 kJ/mol for the process
BaSO4 (s)  Ba2+ (aq) + SO42- (aq)
What is the [Ba2+] in the intestinal tract? (Assume that the only source of SO42- is the
ingested slurry).
7. The air pollutant nitrogen monoxide is produced in automobile engines because of the high
temperature reaction of N2 (g) with O2 (g):
N2 (g) + O2 (g)
2 NO (g)
ΔH˚ = +180.5 kJ
At a temperature of 2300. K, an equilibrium mixture of reactants and products is found to
contain 5.29 atm of NO (g), 129.5 atm N2 (g) and 129.5 atm O2 (g).
a) Would this reaction be considered product-favored at 2300 K?
b) What is the value of ΔS˚ (in J/K) at 2300 K for this reaction?
Dr. White
Chem 1B
3
8. You have a mixture initially containing [CO] = 0.0102 M and [Cl2] = 0.0069 M at 600. K that
reacts according to
CO (g) + Cl2 (g)
COCl2 (g)
If [Cl2] = 0.00301 M at equilibrium, calculate ΔG˚ for this reaction at 600. K and explain what it
tells you about this process.
9. At what temperature will the equilibrium constant for the formation of NOCl (g) be equal to
1.00 x 10 3? Data for this reaction at 25°C are: 2 NO (g) + Cl2 (g) ⇄ 2 NOCl (g) ∆G° = -40.9
kJ/mole ∆H° = -77.1 kJ/mole ∆S° = -121.3 J/mole K (You can assume that ∆H° and ∆S° do
not change much with temperature, but ∆G° will.)
10. At 298 K, ∆Gf°[CO(g)] = -137.2 kJ/mole and K p = 6.5 x 1011 for the reaction CO (g) + Cl2
(g) ⇄ COCl2 (g). Use these data to determine ∆Gf°[COCl2 (g)].
11. Consider the following reaction and it’s ΔG° and ΔH° for parts a-d below
CO2 (g) + 4 H2 (g)  CH4 (g) + 2 H2O (g)
ΔG° = -32.3 kJ/mol at 550°C; ΔH° = 41.2 kJ/mol over a wide range of temperatures
a. What is the value of the Gibbs free-energy change for a mixture of gases that contain the
following pressures at 550°C?
Substance Pressure
CO2
0.90 atm
H2
2.00 atm
CH4
0.10 atm
H2 O
0.50 atm
b. Based on your answer in part a, which of the following is true? (Circle ONE)
The reaction is
product-favored
The reaction is
reactant-favored
The reaction is
spontaneous
The reaction is nonspontaneous
c. What is the value for the standard free energy change of this reaction at 25°C?
d. Based on your answer in part c, which of the following is true? (Circle ONE)
The reaction is
product-favored
The reaction is
reactant-favored
The reaction is
spontaneous
The reaction is nonspontaneous