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Problem 63a,b
Classify each of the following reactions as one of the four possible types summarized in Table 19.3: (i) spontanous at all temperatures; (ii) not spontaneous at any temperature; (iii) spontaneous at low T but not spontaneous at high T; (iv) spontaneous at high T but not spontaneous at low T.
(a) N2(g) + 3 F2(g) → 2 NF3(g) ΔH° = -249 kJ; ΔS° = -278 J/K
(b) N2(g) + 3 Cl2(g) → 2 NCl3(g) ΔH° = 460 kJ; ΔS° = -275 J/K
Problem 63c
Classify each of the following reactions as one of the four possible types summarized in Table 19.3: (i) spontaneous at all temperatures; (ii) not spontaneous at any temperature; (iii) spontaneous at low T but not spontaneous at high T; (iv) spontaneous at high T but not spontaneous at low T.
(c) N2F4(g) ⟶ 2 NF2(g) ΔH° = 85 kJ; ΔS° = 198 J/K
Problem 64
From the values given for ΔH° and ΔS°, calculate ΔG° for each of the following reactions at 298 K. If the reaction is not spontaneous under standard conditions at 298 K, at what temperature (if any) would the reaction become spontaneous?
a. 2 PbS(s) + 3 O2(g) → 2 PbO(s) + 2 SO2(g) ΔH° = −844 kJ; ΔS° = −165 J/K
b. 2 POCl3(g) → 2 PCl3(g) + O2(g) ΔH° = 572 kJ; ΔS° = 179 J/K
- A particular constant-pressure reaction is barely spontaneous at 390 K. The enthalpy change for the reaction is +23.7 kJ. Estimate ΔS for the reaction.
Problem 65
- For a particular reaction, ΔH = -32 kJ and ΔS = -98 J>K. Assume that ΔH and ΔS do not vary with temperature. (a) At what temperature will the reaction have ΔG = 0? (b) If T is increased from that in part (a), will the reaction be spontaneous or nonspontaneous?
Problem 67
Problem 68
Reactions in which a substance decomposes by losing CO are called decarbonylation reactions. The decarbonylation of acetic acid proceeds according to: CH3COOH(l) → CH3OH(g) + CO(g) By using data from Appendix C, calculate the minimum temperature at which this process will be spontaneous under standard conditions. Assume that ΔH° and ΔS° do not vary with temperature.
Problem 69b
Consider the following reaction between oxides of nitrogen: NO2(g) + N2O(g) → 3 NO(g) (b) Calculate ΔG at 800 K, assuming that ΔH° and ΔS° do not change with temperature. Under standard conditions is the reaction spontaneous at 800 K?
Problem 69c
Consider the following reaction between oxides of nitrogen: NO2(g) + N2O(g) → 3 NO(g) (c) Calculate ΔG at 1000 K. Is the reaction spontaneous under standard conditions at this temperature?
Problem 70b
Methanol (CH3OH) can be made by the controlled oxidation of methane: CH4(g) + 12 O2(g) → CH3OH(g) (b) Will ΔG for the reaction increase, decrease, or stay unchanged with increasing temperature?
Problem 72
(a) Using data in Appendix C, estimate the temperature at which the free-energy change for the transformation from I2(s) to I2(g) is zero. (b) Use a reference source, such as Web Elements (www.webelements.com), to find the experimental melting and boiling points of I2. (c) Which of the values in part (b) is closer to the value you obtained in part (a)?
- Acetylene gas, C2H2(g), is used in welding. (b) How much heat is produced in burning 1 mol of C2H2 under standard conditions if both reactants and products are brought to 298 K?
Problem 73
Problem 74a
The fuel in high-efficiency natural-gas vehicles consists primarily of methane (CH4). (a) How much heat is produced in burning 1 mol of CH4(g) under standard conditions if reactants and products are brought to 298 K and H2O(l) is formed?
- Indicate whether ΔG increases, decreases, or stays the same for each of the following reactions as the partial pressure of O2 is increased: (a) 2 CO(g) + O2(g) → 2 CO2(g) (b) 2 H2O2(l) → 2 H2O(l) + O2(g) (c) 2 KClO3(s) → 2 KCl(s) + 3 O2(g)
Problem 75
- Indicate whether ΔG increases, decreases, or does not change when the partial pressure of H₂ is increased in each of the following reactions: (a) N₂(g) + 3 H₂(g) ⇌ 2 NH₃(g) (b) 2 HBr(g) ⇌ H₂(g) + Br₂(g) (c) 2 H₂(g) + C₂H₂(g) ⇌ C₂H₆(g)
Problem 76
Problem 77
Consider the reaction 2 NO2(g) → N2O4(g). (a) Using data from Appendix C, calculate ΔG° at 298 K. (b) Calculate ΔG at 298 K if the partial pressures of NO2 and N2O4 are 0.40 atm and 1.60 atm, respectively.
Problem 78a
Consider the reaction 3 CH4(g) → C3H8(g) + 2 H2(g). (a) Using data from Appendix C, calculate ΔG° at 298 K.
Problem 78b
Consider the reaction 3 CH4(g) → C3H8(g) + 2 H2(g). (b) Calculate ΔG at 298 K if the reaction mixture consists of 40.0 atm of CH4, 0.0100 atm of C3H8(g), and 0.0180 atm of H2.
- Use data from Appendix C to calculate the equilibrium constant, K, and ΔG° at 298 K for each of the following reactions: (a) H2(g) + I2(g) ⇌ 2 HI(g) (b) C2H5OH(g) ⇌ C2H4(g) + H2O(g) (c) 3 C2H2(g) ⇌ C6H6(g)
Problem 79
Problem 81a
Consider the decomposition of barium carbonate: BaCO3(s) ⇌ BaO(s) + CO2(g) Using data from Appendix C, calculate the equilibrium pressure of CO2 at (a) 298 K.
Problem 81b
Consider the decomposition of barium carbonate: BaCO3(s) ⇌ BaO(s) + CO2(g) Using data from Appendix C, calculate the equilibrium pressure of CO2 at (b) 1100 K.
Problem 83a
The value of Ka for nitrous acid (HNO2) at 25 °C is given in Appendix D. (a) Write the chemical equation for the equilibrium that corresponds to Ka.
Problem 83b
The value of Ka for nitrous acid (HNO2) at 25 °C is given in Appendix D. (b) By using the value of Ka, calculate ΔG° for the dissociation of nitrous acid in aqueous solution.
Problem 83c
The value of Ka for nitrous acid (HNO2) at 25 °C is given in Appendix D. (c) What is the value of ΔG at equilibrium?
Problem 83d
The value of Ka for nitrous acid (HNO2) at 25 °C is given in Appendix D. (d) What is the value of ΔG when [H+] = 5.0⨉10-2 M, [NO2-] = 6.0⨉10-4 M, and [HNO2] = 0.20 M?
Problem 84a
The Kb for methylamine (CH3NH2) at 25 °C is given in Appendix D. (a) Write the chemical equation for the equilibrium that corresponds to Kb.
Problem 84d
The Kb for methylamine (CH3NH2) at 25 °C is given in Appendix D. (d) What is the value of ΔG when [H+] = 6.7 × 10-9 M, [CH3NH3+] = 2.4 × 10-3 M, and [CH3NH2] = 0.098 M?
Problem 85a
(a) Which of the thermodynamic quantities T, E, q, w, and S are state functions? (b) Which depend on the path taken from one state to another?
Problem 85d
(d) For a reversible isothermal process, write an expression for ΔE in terms of q and w and an expression for ΔS in terms of q and T.
Problem 86a
The crystalline hydrate Cd(NO3)2⋅4 H2O(s) loses water when placed in a large, closed, dry vessel at room temperature: Cd(NO3)2⋅4 H2O(s) → Cd(NO3)2(s) + 4 H2O(g) This process is spontaneous and ΔH° is positive at room temperature.
(a) What is the sign of ΔS° at room temperature?
Problem 86b
The crystalline hydrate Cd(NO3)2⋅4 H2O(s) loses water when placed in a large, closed, dry vessel at room temperature: Cd(NO3)2⋅4 H2O(s) → Cd(NO3)2(s) + 4 H2O(g) This process is spontaneous and ΔH° is positive at room temperature.
(b) If the hydrated compound is placed in a large, closed vessel that already contains a large amount of water vapor, does ΔS° change for this reaction at room temperature?