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- 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?
Problem 74b
The fuel in high-efficiency natural-gas vehicles consists primarily of methane (CH4). (b) What is the maximum amount of useful work that can be accomplished under standard conditions by this system?
- 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 80a
Using data from Appendix C, write the equilibrium-constant expression and calculate the value of the equilibrium constant and the free-energy change for these reactions at 298 K: (a) NaHCO3(s) ⇌ NaOH(s) + CO2(g)
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 82
Consider the reaction PbCO3(s) ⇌ PbO(s) + CO2(g) Using data in Appendix C, calculate the equilibrium pressure of CO2 in the system at (a) 400 °C (b) 180 °C.
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?
- (c) How many reversible paths are there between two states of a system?
Problem 85
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?
- Indicate whether each of the following statements is true or false. If it is false, correct it. (a) The feasibility of manufacturing NH3 from N2 and H2 depends entirely on the value of ΔH for the process N2(g) + 3 H2(g) → 2 NH3(g). (e) Spontaneous processes are those that are exothermic and that lead to a higher degree of order in the system.
Problem 87
Problem 88
For each of the following processes, indicate whether the signs of ΔS and ΔH are expected to be positive, negative, or about zero. (a) A solid sublimes. (b) The temperature of a sample of Co(s) is lowered from 60 °C to 25 °C. (c) Ethyl alcohol evaporates from a beaker. (d) A diatomic molecule dissociates into atoms. (e) A piece of charcoal is combusted to form CO2(g) and H2O(g).
Problem 89
The reaction 2 Mg(s) + O2(g) ⟶ 2 MgO(s) is highly spontaneous. A classmate calculates the entropy change for this reaction and obtains a large negative value for ΔS°. Did your classmate make a mistake in the calculation? Explain.
Problem 90f
Consider a system that consists of two standard playing dice, with the state of the system defined by the sum of the values shown on the top faces. (f) Calculate the absolute entropy of the two-dice system.
- Ammonium nitrate dissolves spontaneously and endothermally in water at room temperature. What can you deduce about the sign of ΔS for this dissolution process?
Problem 91
Problem 92c
A standard air conditioner involves a refrigerant that is typically now a fluorinated hydrocarbon, such as CH2F2. An air-conditioner refrigerant has the property that it readily vaporizes at atmospheric pressure and is easily compressed to its liquid phase under increased pressure. The operation of an air conditioner can be thought of as a closed system made up of the refrigerant going through the two stages shown here (the air circulation is not shown in this diagram).
During expansion, the liquid refrigerant is released into an expansion chamber at low pressure, where it vaporizes. The vapor then undergoes compression at high pressure back to its liquid phase in a compression chamber. (c) In a central air-conditioning system, one chamber is inside the home and the other is outside. Which chamber is where, and why?