Ch.18 - Free Energy and Thermodynamics

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Tro 4th Edition

Ch.18 - Free Energy and Thermodynamics

Problema 67

Determine ΔG° for the reaction: Fe₂O₃(s) + 3 CO(g) → 2 Fe(s) + 3 CO₂(g) Use the following reactions with known ΔG°_rxnvalues:

2 Fe(s) + 3/2 O₂(g) → Fe₂O₃(s) ΔG°_rxn= -742.2 kJ

CO(g) + 12 O₂( g) → CO₂(g) ΔG°_rxn= -257.2 kJ

Problema 68

Calculate ΔG°rxn for the reaction: CaCO3(s) → CaO(s) + CO2(g). Use the following reactions and given ΔG°rxn values: Ca(s) + CO2(g) + 1/2 O2(g) → CaCO3(s) ΔG°rxn = -734.4 kJ, 2 Ca(s) + O2(g) → 2 CaO(s) ΔG°rxn = -1206.6 kJ.

Problema 69

Consider the sublimation of iodine at 25.0 °C: I2(s) → I2(g). a. Find ΔG°rxn at 25.0 °C.

Problema 69b

Consider the sublimation of iodine at 25.0 °C : I₂(s) → I₂(g) b. Find ΔG°_rxnat 25.0 °C under the following nonstandard conditions: i. P_I2 = 1.00 mmHg ii. P_I2 = 0.100 mmHg

Problema 69c

Consider the sublimation of iodine at 25.0 °C : I₂(s) → I₂(g) c. Explain why iodine spontaneously sublimes in open air at 25.0 °C

Problema 70a

Consider the evaporation of methanol at 25.0 °C : CH₃OH(l) → CH₃OH(g) a. Find ΔG°_r at 25.0 °C.

Problema 70b

Consider the evaporation of methanol at 25.0 °C : CH₃OH(l) → CH₃OH(g) b. Find ΔG_r at 25.0 °C under the following nonstandard conditions: i. P_CH3OH = 150.0 mmHg ii. P_CH3OH= 100.0 mmHg iii. P_CH3OH = 10.0 mmHg

Problema 70c

Consider the evaporation of methanol at 25.0 °C : CH₃OH(l) → CH₃OH(g) c. Explain why methanol spontaneously evaporates in open air at 25.0 °C

Problema 71

Consider the reaction: CH3OH(g) → CO(g) + 2 H2(g). Calculate ΔG for this reaction at 25 °C under the following conditions: i. PCH3OH = 0.855 atm ii. PCO = 0.125 atm iii. PH2 = 0.183 atm.

Problema 72

Consider the reaction: CO₂(g) + CCl₄(g) ⇌ 2 COCl₂(g) Calculate ΔG for this reaction at 25 °C under the following conditions: i. P_CO2 = 0.112 atm ii. P_CCl4 = 0.174 atm iii. P_COCl2 = 0.744 atm

Problema 73a

Use data from Appendix IIB to calculate the equilibrium constants at 25 °C for each reaction. a. 2 CO(g) + O₂(g) ⇌ 2 CO₂(g)

Problema 73b

Use data from Appendix IIB to calculate the equilibrium constants at 25 °C for each reaction. b. 2 H₂S(g) ⇌ 2 H₂(g) + S₂(g)

Problema 74

Use data from Appendix IIB to calculate the equilibrium constants at 25 °C for each reaction. ΔG°f for BrCl(g) is -1.0 kJ/mol. a. 2 NO2(g) ⇌ N2O4(g) b. Br2(g) + Cl2(g) ⇌ 2 BrCl(g)

Problema 75

Consider the reaction: CO(g) + 2 H2(g) ⇌ CH3OH(g) with Kp = 2.26 * 10^4 at 25°C. Calculate ΔG°rxn for the reaction at 25°C under each of the following conditions: a. standard conditions b. at equilibrium c. PCH3OH = 1.0 atm; PCO = PH2 = 0.010 atm

Problema 76a

Consider the reaction: I₂(g) + Cl₂(g) ⇌ 2 ICl(g) K_p = 81.9 at 25 °C Calculate ΔG_rxn for the reaction at 25 °C under each of the following conditions: a. standard conditions

Problema 76b

Consider the reaction: I₂(g) + Cl₂(g) ⇌ 2 ICl(g) K_p = 81.9 at 25 °C Calculate ΔG_rxn for the reaction at 25 °C under each of the following conditions: b. at equilibrium

Problema 76c

Consider the reaction: I₂(g) + Cl₂(g) ⇌ 2 ICl(g) K_p = 81.9 at 25 °C Calculate ΔG_rxnfor the reaction at 25 °C under each of the following conditions: c. P_ICl = 2.55 atm; P_I2 = 0.325 atm; P_Cl2 = 0.221 atm

Problema 77

Is the value of the equilibrium constant at 525 K for each reaction in Problem 73 estimated correctly?

Problema 78

Estimate the value of the equilibrium constant at 655 K for each reaction in Problem 74. (ΔHf° for BrCl is 14.6 kJ/mol.)

Problema 80

Consider the reaction: 2 NO(g) + O₂(g) ⇌ 2 NO₂(g) The following data show the equilibrium constant for this reaction measured at several different temperatures. Use the data to find ΔH°_rxnand ΔS°_rxnfor the reaction.

Problema 81

The change in enthalpy (ΔH°_rxn) for a reaction is -25.8 kJ/mol. The equilibrium constant for the reaction is 1.4⨉10³ at 298 K. What is the equilibrium constant for the reaction at 655 K?

Problema 82

A reaction has an equilibrium constant of 8.5⨉10³ at 298 K. At 755 K, the equilibrium constant is 0.65. Find ΔH°_rxnfor the reaction.

Problema 83a

Determine the sign of ΔS_sys for each process. a. water boiling

Problema 83b

Determine the sign of ΔS_sys for each process. b. water freezing

Problema 85

Our atmosphere is composed primarily of nitrogen and oxygen, which coexist at 25 °C without reacting to any significant extent. However, the two gases can react to form nitrogen monoxide according to the reaction: N2(g) + O2(g) → 2 NO(g). a. Calculate ΔG° and Kp for this reaction at 298 K. Is the reaction spontaneous? b. Estimate ΔG° at 2000 K. Does the reaction become more spontaneous as temperature increases?

Problema 86

Nitrogen dioxide, a pollutant in the atmosphere, can combine with water to form nitric acid. One of the possible reactions is shown here. Calculate ΔG° and K_p for this reaction at 25 °C and comment on the spontaneity of the reaction. 3 NO₂(g) + H₂O(l)→ 2 HNO₃(aq) + NO(g)

Problema 87

Ethene (C₂H₄) can be halogenated by the reaction: C₂H₄(g) + X₂(g) → C₂H₄X₂(g) where X₂can be Cl₂, Br₂, or I₂. Use the thermodynamic data given to calculate ΔH°, ΔS°, ΔG°, and Kp for the halogenation reaction by each of the three halogens at 25 °C. Which reaction is most spontaneous? Least spontaneous? What is the main factor responsible for the difference in the spontaneity of the three reactions? Does higher temperature make the reactions more spontaneous or less spontaneous?

Compound ΔH°_f (kJ/mol) S° (J/mol·K)

C₂H₄Cl₂(g) -129.7 308.0

C₂H₄Br₂(g) +38.3 330.6

C₂H₄I₂(g) +66.5 347.8

Problema 88

H₂ reacts with the halogens (X₂) according to the reaction: H₂(g) + X₂(g) → 2 HX(g) where X₂ can be Cl₂, Br₂, or I₂. Use the thermodynamic data in Appendix IIB to calculate ΔH°, ΔS°, ΔG°, and K_p for the reaction between hydrogen and each of the three halogens. Which reaction is most spontaneous? Least spontaneous? What is the main factor responsible for the difference in the spontaneity of the three reactions? Does higher temperature make the reactions more spontaneous or less spontaneous?

Problema 89a

Consider this reaction occurring at 298 K: N₂O(g) + NO₂(g) ⇌ 3 NO(g) a. Show that the reaction is not spontaneous under standard conditions by calculating ΔG°_rxn.

Problema 89b

Consider this reaction occurring at 298 K: N₂O(g) + NO₂(g) ⇌ 3 NO(g) b. If a reaction mixture contains only N₂O and NO₂ at partial pressures of 1.0 atm each, the reaction will be spontaneous until some NO forms in the mixture. What maximum partial pressure of NO builds up before the reaction ceases to be spontaneous?