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- For each of the following pairs, predict which substance has the higher entropy per mole at a given temperature: (a) Ar(l) or Ar(g) (b) He(g) at 3 atm pressure or He(g) at 1.5 atm pressure (c) 1 mol of Ne(g) in 15.0 L or 1 mol of Ne(g) in 1.50 L (d) CO2(g) or CO2(s)
Problem 39
Problem 40a
For each of the following pairs, predict which substance possesses the larger entropy per mole: (a) 1 mol of O2(g) at 300 °C, 0.01 atm, or 1 mol of O3(g) at 300 °C, 0.01 atm
Problem 41a
Predict the sign of the entropy change of the system for each of the following reactions: (a) N2(g) + 3 H2(g) → 2 NH3(g)
Problem 41b
Predict the sign of the entropy change of the system for each of the following reactions: (b) CaCO3(s) → CaO(s) + CO2(g)
Problem 41c
Predict the sign of the entropy change of the system for each of the following reactions: (c) 3 C2H2(g) → C6H6(g)
Problem 41d
Predict the sign of the entropy change of the system for each of the following reactions: (d) Al2O3(s) + 3 H2(g) → 2 Al(s) + 3 H2O(g)
Problem 42a
Predict the sign of ΔSsys for each of the following processes: (a) Molten gold solidifies.
Problem 42b
Predict the sign of ΔSsys for each of the following processes: (b) Gaseous Cl2 dissociates in the stratosphere to form gaseous Cl atoms.
Problem 42c
Predict the sign of ΔSsys for each of the following processes: (c) Gaseous CO reacts with gaseous H2 to form liquid methanol, CH3OH.
Problem 42d
Predict the sign of ΔSsys for each of the following processes: (d) Calcium phosphate precipitates upon mixing Ca(NO3)2(aq) and (NH4)3PO4(aq).
- In each of the following pairs, which compound would you expect to have the higher standard molar entropy: (a) C2H2(g) or C2H6(g)? (b) CO2(g) or CO(g)?
Problem 45
Problem 46
Cyclopropane and propylene are isomers that both have the formula C3H6. Based on the molecular structures shown, which of these isomers would you expect to have the higher standard molar entropy at 25 °C?
- Predict which member of each of the following pairs has the greater standard entropy at 25°C: (a) Sc(s) or Sc(g). Use Appendix C to find the standard entropy of each substance. (b) NH3(g) or NH3(aq). Use Appendix C to find the standard entropy of each substance. (c) O2(g) or O3(g). Use Appendix C to find the standard entropy of each substance. (d) C(graphite) or C(diamond). Use Appendix C to find the standard entropy of each substance.
Problem 47
- Predict which member of each of the following pairs has the greater standard entropy at 25°C: (a) C6H6(l) or C6H6(g). Use Appendix C to find the standard entropy of each substance. (b) CO(g) or CO2(g). Use Appendix C to find the standard entropy of each substance. (c) 1 mol N2O4(g) or 2 mol NO2(g). Use Appendix C to find the standard entropy of each substance. (d) HCl(g) or HCl(aq). Use Appendix C to find the standard entropy of each substance.
Problem 48
- The standard entropies at 298 K for certain group 4A elements are: C(s, diamond) = 2.43 J>mol@K, Si1s2 = 18.81 J>mol@K, Ge1s2 = 31.09 J>mol@K, and Sn1s2 = 51.818 J>mol@K. All but Sn have the same (diamond) structure. How do you account for the trend in the S° values?
Problem 49
- Three of the forms of elemental carbon are graphite, diamond, and buckminsterfullerene. The entropies at 298 K for graphite and diamond are listed in Appendix C. (b) What would you expect for the S° value of buckminsterfullerene (Figure 12.49, p. 509) relative to the values for graphite and diamond? Explain.
Problem 50
Problem 51
Using S° values from Appendix C, calculate ΔS° values for the following reactions. In each case, account for the sign of ΔS°.
(a) C2H4(g) + H2(g) → C2H6(g)
(b) N2O4(g) → 2 NO2(g)
(c) Be(OH)2(s) → BeO(s) + H2O(g)
(d) 2 CH3OH(g) + 3 O2(g) ⟶ 2 CO2(g) + 4 H2O(g)
- Calculate ΔS° values for the following reactions by using tabulated S° values from Appendix C. In each case, explain the sign of ΔS°. (a) HNO3(g) + NH3(g) → NH4NO3(s) (b) 2 Fe2O3(s) → 4 Fe(s) + 3 O2(g) (c) CaCO3(s, calcite) + 2 HCl(g) → CaCl2(s) + CO2(g) + H2O(l) (d) 3 C2H6(g) → C6H6(l) + 6 H2(g)
Problem 52
Problem 53a
(a) For a process that occurs at constant temperature, does the change in Gibbs free energy depend on changes in the enthalpy and entropy of the system?
Problem 53b
(b) For a certain process that occurs at constant T and P, the value of ΔG is positive. Is the process spontaneous?
- (a) Is the standard free-energy change, ΔG°, always larger than ΔG? (b) For any process that occurs at constant temperature and pressure, what is the significance of ΔG = 0? (c) For a certain process, ΔG is large and negative. Does this mean that the process necessarily has a low activation barrier?
Problem 54
Problem 55b
For a certain chemical reaction, ΔH° = -35.4 kJ and ΔS° = -85.5 J/K. (b) Does the reaction lead to an increase or decrease in the randomness or disorder of the system?
Problem 55c,d
For a certain chemical reaction, ΔH° = -35.4 kJ and ΔS° = -85.5 J/K. (c) Calculate ΔG° for the reaction at 298 K. (d) Is the reaction spontaneous at 298 K under standard conditions?
- A certain reaction has ΔH° = +23.7 kJ and ΔS° = +52.4 J>K. (c) Calculate ΔG° for the reaction at 298 K. (d) Is the reaction spontaneous at 298 K under standard conditions?
Problem 56
- Using data in Appendix C, calculate ΔH°, ΔS°, and ΔG° at 298 K for each of the following reactions. (a) H₂(g) + F₂(g) → 2 HF(g) (b) C(s, graphite) + 2 Cl₂(g) → CCl₄(g) (c) 2 PCl₃(g) + O₂(g) → 2 POCl₃(g) (d) 2 CH₃OH(g) + H₂(g) → C₂H₆(g) + 2 H₂O(g)
Problem 57
Problem 58
Use data in Appendix C to calculate ΔH°, ΔS°, and ΔG° at 25 °C for each of the following reactions.
a. 4 Cr(s) + 3 O2(g) → 2 Cr2O3(s)
b. BaCO3(s) → BaO(s) + CO2(g)
c. 2 P(s) + 10 HF(g) → 2 PF5(g) + 5 H2(g)
d. K(s) + O2(g) → KO2(s)
Problem 59
Using data from Appendix C, calculate ΔG° for the following reactions. Indicate whether each reaction is spontaneous at 298 K under standard conditions.
(a) 2 SO2(g) + O2(g) → 2 SO3(g)
(b) NO2(g) + N2O(g) → 3 NO(g)
(c) 6 Cl2(g) + 2 Fe2O3(s) → 4 FeCl3(s) + 3 O2(g)
(d) SO2(g) + 2 H2(g) → S(s) + 2 H2O(g)
Problem 60
Using data from Appendix C, calculate the change in Gibbs free energy for each of the following reactions. In each case, indicate whether the reaction is spontaneous at 298 K under standard conditions.
(a) 2 Ag(s) + Cl2(g) → 2 AgCl(s)
(b) P4O10(s) + 16 H2(g) → 4 PH3(g) + 10 H2O(g)
(c) CH4(g) + 4 F2(g) → CF4(g) + 4 HF(g)
(d) 2 H2O2(l) → 2 H2O(l) + O2(g)
- Without using thermochemical data, predict whether ΔG° for the reaction involving octane (1C8H182) is more negative or less negative than ΔH°.
Problem 61
- Sulfur dioxide reacts with strontium oxide as follows: SO2(g) + SrO(g) → SrSO3(s). (b) If you had only standard enthalpy data for this reaction, how would you estimate the value of ΔG° at 298 K, using data from Appendix C on other substances?
Problem 62