Page 145 - Bruno Linder Elementary Physical Chemistry

August 18, 2010 11:37 9in x 6in b985-appA Elementary Physical Chemistry

130 Elementary Physical Chemistry

8. The standard Gibbs free energy for a given reaction is ∆G o =
−1
40 kJmol at 1500 K. The enthalpy change for the reaction is ∆H =
250 kJmol −1 at 1500K and approximately constant.
(a) Calculate the equilibrium constant at T = 1500 K.
(b) Calculate the temperature at which the equilibrium constant is
K =1.
9. Which of the following reactions has a K> 1?

(a) NH 4 Cl → HCl(g) + NH 3 (g)
(b) Fe(s) + 2H 2 S(g) → FeS 2 (s) + 2H 2(g)
(c) H 2 SO 4 (l) + 2H 2 (g) → 2H 2 O+ H 2 S(g)
10. Which of the reactions in Problem 9 will be enhanced (yield more
products) by increasing the temperature?

Problem Set IV. Chapter 6
1. A liquid in equilibrium with its vapor consists of substances A, B and C.
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If the volume of the vapor phase is 100 m at 298.15K and the partial
pressures of the three substances are respectively, P a (A) = 2.33 kPa,
P a (B) = 1.43 kPa and P a (C) = 0.26 kPa, calculate
(a) the mole fraction of each substance in the vapor phase,
(b) the number of moles of each substance in the vapor phase.
2. The partial molar volumes of benzene [C 6 H 6 (l)] and cyclohexane
3
[(C 6 H 12 (l)] are respectively 75 and 80 cm mol −1 . The mole fraction
of benzene is 0.6.

(a) What is the mole fraction of cyclohexane?
(b) What is the weight per mole of the combined substances?
(c) What is the volume of a solution whose total mass is 500 g?
3. The mole fraction, x B , and partial pressure, P B,of three solutions ofa
substance is
x B 0.010 0.024 0.038
P B /kPa 64.0 153.8 243.6
Calculate Henry’s Law constant, K H .
4. (a) The partial vapor pressure of oxygen [O 2(g)] in air at sea level is
21.0 kPa at 298.15 K. Henry’s Law constant at that temperature