Engel & Reid, 3rd
Chapter 6 Answers
CHM 3001
P6.33) A sample containing 2.50 mol of an ideal gas at 325 K is expanded from an initial volume of
10.5 L to a final volume of 60.0 L. Calculate the final pressure. Calculate DG and DA for this process
for (a) an isothermal reversible path and (b) an isothermal expansion against a constant external pressure
equal to the final pressure. Explain why DG and DA do or do not differ from one another.
Ans.
a)
b)
ΔG = -11.8 x 103 J, ΔA = -11.8 x 103 J
ΔG = -11.8 x 103 J, ΔA = -11.8 x 103 J
P6.32) Calculate DGR for the reaction CO(g) + ½ O2(g) ↔ CO2(g) at 298.15 K. Calculate DGR at 600.
K assuming that DH R is constant in the temperature interval of interest.
Hint: Use Table 4.1.
Ans. ΔGRo = -257.2 kJ/mol at 298 K, ΔGRo = -231.1 kJ/mol at 600. K
P6.17) Calculate µOmixture ( 298.15 K, 1 bar ) for oxygen in air, assuming that the mole fraction of O2 in
2
air is 0.210. Use the conventional molar Gibbs energy defined in Section 6.17.
Hint: Ignore the last sentence. Instead, recall that µ is the molar Gibbs energy for a pure substance and
recognize that Hmo = ΔHfo = 0 for any element in its stable state so µO2o can be calculated using Table
4.1.
Ans. µOmixture
( 298.15 K, 1 bar )= -65.05 kJ mol-1
2
P6.4) Consider the equilibrium NO2(g) ↔ NO(g) + 1/2O2(g). One mole of NO2(g) is placed in a vessel
and allowed to come to equilibrium at a total pressure of 1 bar. An analysis of the contents of the vessel
gives the following results:
T
700. K
800. K
PNO
0.872
2.50
PNO2
a. Calculate KP at 700. and 800. K.
b. Calculate DGR and DH R for this reaction at 298.15 K using only the data in this problem. Assume that
DH R is independent of temperature.
c. Calculate DH R using the data tables and compare your answer with that obtained in part (b).
Note: Use only the data given in this problem, not the Appendix, except for part (c).
Ans.
a)
b)
c)
KP = 0.380 at 700 K, KP = 1.28 at 800 K
ΔGRo = 35.0 kJ/mol, ΔHRo = 56.7 kJ/mol at 298 K
ΔHRo = 58.1 kJ/mol
P6.24) Consider the reaction FeO(s) + CO(g) ↔ Fe(s) + CO2(g) for which KP is found to have the
following values:
T
KP
700.ºC
0.688
1200.ºC
0.310
a. Calculate DGR , DS R and DH R for this reaction at 700.ºC. Assume that DH R is independent of
temperature.
b. Calculate the mole fraction of CO2(g) present in the gas phase at 700.ºC.
Note: Use only the data given in this problem, not the Appendix.
Ans.
a)
b)
ΔGRo = 3.03 kJ/mol, ΔHRo = -19.0 kJ/mol, ΔSRo = -22.6 J/mol K
XCO2 = 0.408
P6.36) Consider the equilibrium in the reaction 3O2(g) ↔2O3(g). Assume DH R is independent of
temperature.
a. Without doing a calculation, predict whether the equilibrium position will shift toward reactants or
products as the pressure is increased.
b. Using only the data tables, predict whether the equilibrium position will shift toward reactants or
products as the temperature is increased.
c. Calculate KP at 600. and 700. K. Compare your results with your answer in part (b).
d. Calculate Kx at 600. K and pressures of 1.00 and 2.25 bar. Compare your results with your answer in
part (a).
Note: Use data in the Appendix for part (c) only.
Ans. a)
Prediction
b)
Prediction
c)
KP =9.0 x 10-33 at 600 K and 3.2 x 10-29 at 700 K.
d)
KX = 9.0 x 10-33 at P = 1.00 bar, 2.0 x 10-32 at 2.25 bar.
P6.13) Ca(HCO3)2(s) decomposes at elevated temperatures according to the stoichiometric equation
Ca(HCO3)2(s) → CaCO3(s) + H2O(g) + CO2(g).
a. If pure Ca(HCO3)2(s) is put into a sealed vessel, the air is pumped out, and the vessel and its contents
are heated, the total pressure is 0.290 bar. Determine KP under these conditions.
b. If the vessel initially also contains 0.120 bar H2O(g), what is the partial pressure of CO2(g) at
equilibrium?
Note: Use only the data given in this problem, not the Appendix.
Ans. a)
KP = 2.10 x 10-2
b)
PCO2 = 0.0969 bar