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- Give an equation that relates the entropy change in the surroundings to the enthalpy change in the system. What is the sign of ∆Ssurr for the following? (a) An exothermic reaction (b) An endothermic reaction
Problem 70
- What are the values of x and y for the following reaction if E° = 0.91 V and ∆G° = -527 kJ?
Problem 71
- Reduction of mercury(II) oxide with zinc gives metallic mercury: (b) Estimate at what temperature, if any, the reaction will become nonspontaneous
Problem 72
- Elemental sulfur is formed by the reaction of zinc sulfide with oxygen: (b) At what temperature, if any, the reaction will become nonspontaneous?
Problem 73
Problem 77a
Phosphorus pentachloride forms from phosphorus trichloride and chlorine:
(a) Use data in Appendix B to calculate ∆Ssys, ∆Ssurr, and ∆Stotal for this reaction. Is the reaction spontaneous under standard-state conditions at 25 °C?
Problem 78a
For the vaporization of benzene, ∆Hvap = 30.7 kJ/mol and ∆Svap = 87.0 J/(K*mol). Calculate ∆Ssurr and ∆Stotal at: (a) 70 °C
Problem 78d
For the vaporization of benzene, ∆Hvap = 30.7 kJ/mol and ∆Svap = 87.0 J/(K*mol). Does benzene boil at 70 °C and 1 atm pressure? Calculate the normal boiling point of benzene.
Problem 85a
Consider a twofold expansion of 1 mol of an ideal gas at 25 °C in the isolated system shown in Figure 18.1. (a) What are the values of ∆H, ∆S, and ∆G for the process?
Problem 85b
Consider a twofold expansion of 1 mol of an ideal gas at 25 °C in the isolated system shown in Figure 18.1. (b) How does this process illustrate the second law of thermodynamics?
- Given the data in Problem 18.78, calculate ∆G for the vaporization of benzene at: (a) 70 °C Predict whether benzene will boil at each of these temperatures and 1 atm pressure.
Problem 86
- Define (a) the standard free-energy change, ∆G°, for a reaction, and (b) the standard free energy of formation, ∆G°f, of a substance.
Problem 92
Problem 93
What is meant by the standard state of a substance?
- Use the data in Appendix B to tell which of the following compounds are thermodynamically stable with respect to their constituent elements at 25 °C: (a) BaCO3(s) (b) HBr(g) (c) N2O(g) (d) C2H4(g).
Problem 98
- Use the data in Appendix B to determine which of the following compounds are thermodynamically stable with respect to their constituent elements at 25 °C.
Problem 99
(a) C6H6(l) (b) NO(g) (c) PH3(g) (d) FeO(s) - Ethanol is manufactured in industry by the hydration of ethylene: Using the data in Appendix B, calculate ∆G° and show that this reaction is spontaneous at 25 °C. Why does this reaction become nonspontaneous at higher temperatures? Estimate the temperature at which the reaction becomes nonspontaneous.
Problem 102
- Consider the conversion of 1,2-dichloroethane to vinyl chloride, the starting material for manufacturing poly(vinyl chloride) (PVC) plastics: Is this reaction spontaneous under standard-state conditions? Would it help to carry out the reaction in the presence of base to remove HCl? Explain. Is it possible to synthesize vinyl chlo-ride from graphite, gaseous H2, and gaseous Cl2 at 25 °C and 1 atm pressure?
Problem 105
- What is the relationship between the free-energy change under nonstandard-state conditions, ∆G, the free-energy change under standard-state conditions, ∆G°, and the reaction quotient, Q?
Problem 106
- Compare the values of ∆G and ∆G° when: (a) Q < 1. (b) Q = 1. (c) Q > 1. Does the thermodynamic tendency for the reaction to occur increase or decrease as Q increases?
Problem 107
- What is the relationship between the standard free-energy change, ∆G°, for a reaction and the equilibrium constant, K? What is the sign of ∆G° when: (a) K > 1? (b) K = 1? (c) K < 1?
Problem 112
- Do you expect a large or small value of the equilibrium constant for a reaction with the following values of ∆G°? (a) ∆G° is positive. (b) ∆G° is negative.
Problem 113
- Ammonium nitrate is dangerous because it decomposes (sometimes explosively) when heated: (a) Using the data in Appendix B, show that this reaction is spontaneous at 25 °C.
Problem 120
Problem 122a,b
Use the data in Appendix B to calculate the equilibrium pressure of CO2 in a closed 1 L vessel that contains each of the following samples:
(a) 15 g of MgCO3 and 1.0 g of MgO at 25 °C
(b) 15 g of MgCO3 and 1.0 g of MgO at 280 °C .
Assume that ∆H° and ∆S° are independent of temperature.
Problem 124d
Consider the Haber synthesis of gaseous NH3 (∆H°f = -46.1 kJ/mol; ∆G°f = -16.5 kJ/mol: (d) What are the equilibrium constants Kp and Kc for the reaction at 350 K? Assume that ∆H° and ∆S° are independent of temperature.
- Is it possible for a reaction to be nonspontaneous yet exo-thermic? Explain.
Problem 125
Problem 126b
Trouton's rule says that the ratio of the molar heat of vaporization of a liquid to its normal boiling point (in kelvin) is approximately the same for all liquids: ∆Hvap/Tbp ≈ 88 J/(K*mol) (b) Explain why liquids tend to have the same value of ∆Hvap/Tbp.
- Tell whether reactions with the following values of ΔH and ΔS are spontaneous or nonspontaneous and whether they are exothermic or endothermic. (a) ΔH = - 48 kJ; ΔS = + 135 J>K at 400 K (b) ΔH = - 48 kJ; ΔS = - 135 J>K at 400 K (c) ΔH = + 48 kJ; ΔS = + 135 J>K at 400 K (d) ΔH = + 48 kJ; ΔS = - 135 J>K at 400 K
Problem 132
- The following reaction, sometimes used in the laboratory to generate small quantities of oxygen gas, has ∆G° = -224.4 kJ/mol at 25°C:
Problem 133
Use the following additional data at 25 °C to calculate the standard molar entropy S° of O2 at 25°C: ∆H°f(KClO3) = -397.7 kJ/mol, ∆H°f(KCl) = -436.5 kJ/mol, S°(KClO3) = 143.1 J/(K*mol), and S°(KCl) = 82.6 J/(K*mol).
- Suppose that a reaction has ΔH = - 33 kJ and ΔS = - 58 J>K. At what temperature will it change from spontaneous to nonspontaneous?
Problem 134
- A mixture of 14.0 g of N2 and 3.024 g of H2 in a 5.00 L container is heated to 400 °C. Use the data in Appendix B to calculate the molar concentrations of N2, H2, and NH3 at equilibrium. Assume that ∆H° and ∆S° are independent of temperature, and remember that the standard state of a gas is defined in terms of pressure.
Problem 136
Problem 138b
The lead storage battery uses the reaction: (b) Calculate ∆G for this reaction on a cold winter's day (10 °F) in a battery that has run down to the point where the sulfuric acid concentration is only 0.100 M.