Chapter 17 – Entropy, Free Energy, and Equilibrium
32.
Calculate G for the reaction 3NO2(g) + H2O(l) → 2HNO3(l) + NO(g).
33.
Ozone (O3) in the atmosphere can react with nitric oxide (NO):
O3(g) + NO(g) → NO2(g) + O2(g).
Calculate the G for this reaction at 25C. (H = –199 kJ/mol, S = –4.1 J/K·mol)
Chapter 17 – Entropy, Free Energy, and Equilibrium
34. Sodium carbonate can be made by heating sodium bicarbonate:
2NaHCO3(s) → Na2CO3(s) + CO2(g) + H2O(g)
Given that H = 128.9 kJ/mol and G = 33.1 kJ/mol at 25C, above what minimum
temperature will the reaction become spontaneous under standard state conditions?
35. The element oxygen was prepared by Joseph Priestley in 1774 by heating mercury(II)
oxide:
HgO(s) → Hg(l) + 1/2O2(g), H = 90.84 kJ/mol.
Estimate the temperature at which this reaction will become spontaneous under standard state
conditions.
S(Hg) = 76.02 J/K·mol
S(O2) = 205.0 J/K·mol
S(HgO) = 70.29 J/K·mol
Chapter 17 – Entropy, Free Energy, and Equilibrium
36. For the reaction H2(g) + S(s) → H2S(g), H = –20.2 kJ/mol and S = +43.1 J/K·mol.
Which of these statements is true?
37.
The normal freezing point of ammonia is –78C. Predict the signs of H, S, and G for ammonia when it freezes at –80C
and 1 atm: NH3(l) → NH3(s).
Chapter 17 – Entropy, Free Energy, and Equilibrium
38. The normal melting point of sulfur is 113 C. If a sample of solid sulfur is at 95 C,
predict the signs of H, S, and G for the melting process at this temperature.
39. The normal boiling point of acetic acid is 118.1C. If a sample of the acetic acid is at
125.2C, predict the signs of H, S, and G for the boiling process at this temperature.
Chapter 17 – Entropy, Free Energy, and Equilibrium
40. Hydrogen peroxide (H2O2) decomposes according to the equation
H2O2(l) → H2O(l) + 1/2O2(g).
Calculate Kp for this reaction at 25C. (H = –98.2 kJ/mol, S = 70.1 J/K·mol)
41.
At 1500C the equilibrium constant for the reaction CO(g) + 2H2(g) CH3OH(g) has the value Kp = 1.4 10–7.
Calculate G for this reaction at 1500C.
Chapter 17 – Entropy, Free Energy, and Equilibrium
42.
Calculate Kp at 298 K for the reaction SO2(g) + NO2(g) SO3(g) + NO(g).
43.
The equilibrium constant at 427C for the reaction N2(g) + 3H2(g) 2NH3(g) is Kp = 9.4 10–5. Calculate the value of
G for the reaction under these conditions.
Chapter 17 – Entropy, Free Energy, and Equilibrium
44.
Determine the equilibrium constant Kp at 25C for the reaction N2(g) + 3H2(g) 2NH3(g).
[Gf (NH3(g)) = –16.6 kJ/mol]
45.
Calculate the equilibrium constant for the decomposition of water
2H2O(l) 2H2(g) + O2(g)
at 25C, given that Gf (H2O(l)) = –237.2 kJ/mol.
Chapter 17 – Entropy, Free Energy, and Equilibrium
46.
Nitrosyl chloride (NOCl) decomposes at elevated temperatures according to the equation
2NOCl(g) 2NO(g) + Cl2(g). Calculate Kp for this reaction at 227C. (H = 81.2 kJ/mol, S = 128 J/K·mol)
47.
The equilibrium constant for the reaction AgBr(s) Ag+(aq) + Br– (aq) is the solubility product constant, Ksp = 7.7 10–
13 at 25C. Calculate G for the reaction when [Ag+] = 1.0 10–2 M and [Br–] = 1.0 10–3 M. Is the reaction spontaneous or
nonspontaneous at these concentrations?
Chapter 17 – Entropy, Free Energy, and Equilibrium
48. For the reaction 2C(graphite) + H2(g) → C2H2(g), G= +209.2 kJ/mol at 25C. If P(H2)
= 100. atm, and P(C2H2) = 0.10 atm, calculate G for this reaction.
49.
For the reaction 2 SO2(g) + O2(g) → 2 SO3(g), if initially P(SO2) = 1.2 atm, P(O2) = 1.8 atm, and P(SO3) = 2.1 atm, calculate
G for this reaction at 25C. The following data is valid at 25C:
Chapter 17 – Entropy, Free Energy, and Equilibrium
50.
For the reaction 2NO(g) + O2(g) → 2NO2(g) if initially P(NO) = 1.5 atm, P(O2) = 1.4 atm, and P(NO2) = 2.0 atm, calculate
G for this reaction at 25C. The following data is valid at 25C:
51.
Determine the equilibrium constant (Kp) at 25C for the reaction
G = –28.5 kJ/mol
Chapter 17 – Entropy, Free Energy, and Equilibrium
52. Kw for the auto-ionization of water, H2O(l) → H+(aq) + OH– (aq), is 1.0 10–14. What are
the signs (+/–) of S and H for the reaction at 25C?
53. Which of the following is consistent with a reaction at equilibrium?
Chapter 17 – Entropy, Free Energy, and Equilibrium
54.
Which of the following is consistent with a reaction that proceeds spontaneously in the forward direction?
55.
Which of the following is consistent with a reaction that proceeds spontaneously in the reverse direction (assume all variables
are in terms of the forward direction only)?
Chapter 17 – Entropy, Free Energy, and Equilibrium
56. The reaction rates of many spontaneous reactions are actually very slow. Which of these
statements is the best explanation for this observation?
57.
The solubility product constant at 25C for AgI(s) in water has the value 8.3 10–17. Calculate Grxn at 25C for the process
AgI(s) Ag+(aq) + I– (aq) where [Ag+] = 9.1 10–9 and [I–] = 9.1 10–9.
Chapter 17 – Entropy, Free Energy, and Equilibrium
58.
Calculate G for the combustion of ethanol vapor, C2H5OH(g), at 750C in oxygen to form carbon dioxide and water vapor.
The following data is valid at 25C:
Chapter 17 – Entropy, Free Energy, and Equilibrium
59.
Find the temperature at which the reaction N2O4(g) 2NO2(g) will be in equilibrium when both gases are present at
partial pressures of 1.00 atm.
Chapter 17 – Entropy, Free Energy, and Equilibrium
60.
Predict the normal boiling point of triethylborane (C6H15B) using the following data:
Chapter 17 – Entropy, Free Energy, and Equilibrium
61.
A sample of solid naphthalene is introduced into an evacuated flask. Use the data below to calculate the equilibrium vapor
pressure of naphthalene (C10H8) in the flask at 35C.
62.
The standard free energy of formation of gaseous hydrogen iodide is 1.30 kJ/mol at 25C. Find Kp for the reaction H2(g) +
I2(s) 2HI(g) at this temperature.
Chapter 17 – Entropy, Free Energy, and Equilibrium
63.
Find the temperature at which Kp = 4.00 for the reaction N2O4(g) 2NO2(g). [Given: at 25C, for NO2(g), Hf = 33.85
kJ/mol, S = 240.46 J/mol·K; for N2O4(g), Hf = 9.66 kJ/mol, S = 304.3 J/mol·K; assume that H and S are
independent of temperature.]
64.
Find the temperature at which Kp = 42.0 for the reaction H2(g) + I2(g) 2HI(g). [Given: at 25C, for H2(g), Hf = 0, S
= 131.0 J/mol·K; for I2(g), Hf = 62.26 kJ/mol, S = 260.6 J/mol·K; for HI(g), Hf = 25.9 kJ/mol, S = 206.3 J/mol·K;
assume that H and S are independent of temperature.]
Chapter 17 – Entropy, Free Energy, and Equilibrium
65.
For the reaction HCONH2(g) NH3(g) + CO(g), Kc = 4.84 at 400 K. If H for this reaction is 29 kJ/mol, find Kc at 500
K.
66.
In the gas phase, formic acid forms a dimer, 2HCOOH(g) (HCOOH)2(g). For this reaction, H = –60.1 kJ/mol and
G = –13.9 kJ/mol at 25C. Find the equilibrium constant (Kp) for this reaction at 75 C.
Chapter 17 – Entropy, Free Energy, and Equilibrium
67.
In the gas phase, methyl isocyanate (CH3NC) isomerizes to acetonitrile (CH3CN),
H3C–NC (g) H3C–CN (g)
with H = –89.5 kJ/mol and G = – 73.8 kJ/mol at 25C. Find the equilibrium constant for this reaction at 100C.