s11Q2W3

# s11Q2W3 - CHEM 0120 Golde SPRING 2011 QUIZ 2 WEEK 3 Tuesday...

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CHEM 0120 SPRING 2011 Tuesday 8:00 AM Golde QUIZ 2 WEEK 3 January 18, 2011 Name_______________________________ 1. a) The reaction HNO 2 + H 2 O H 3 O + + - 2 NO (1) has an equilibrium constant, K c = 4.5 x 10 -4 . Calculate K c for the reaction: H 3 O + + - 2 NO HNO 2 + H 2 O. (2) b) What is the active species in the strong acid, HNO 3 ? c) Would you expect the reaction of a strong acid with KNO 2 to have a large or a small value of K c ? Give your reasoning. Hint: this question is related to Question 1(a)!! 2. At a certain temperature, the equilibrium constant of the reaction N 2 (g) + 3H 2 (g) 2NH 3 (g) is K p = 7.52. If an equilibrium mixture contains 4.19 atm of N 2 and 0.564 atm of H 2 , what is the pressure of NH 3 in this mixture? Hint: write the equilibrium constant expression. ANSWERS 1. a) The reaction has been reversed, so K c = 4 - 10 x 4.5 1 = 2.2 x 10 3 . b,c) The active species in a strong acid is H 3 O + and that in KNO 2 is the NO 2 - ion. Thus, the cited reaction is the same as reaction (2), so a large value of K c is expected. 2. K p = 2 3 3 2 2 p(NH ) p(N ) x p(H ) p(NH 3 ) 2 = 7.52 x 4.19 x (0.564) 3 = 5.65 p(NH 3 ) = 2.38 atm CHEM 0120 SPRING 2011 Tuesday 1:00 PM Golde QUIZ 2 WEEK 3 January 18, 2011 For Make-up Only Regular recitation Day: Time: instructor: Quiz Score: Group score: Scores recorded by:

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Name_______________________________ 1. Consider the following equilibria, occurring at room temperature. Br 2 (l) Br 2 (g) K p = 0.35 (1) H 2 O(l) H 2 O(g) K p = 0.031 (2) a) Write the K p equilibrium constant expression for reaction (1) b) Which chemical, Br 2 or H 2 O, has the greater equilibrium vapor pressure at room temperature? Give your reasoning. 2. At 600 K, 4.20 moles of NO and 3.40 moles of Cl 2 were introduced into a 1.0 liter container (no ClNO initially). When the reaction 2NO (g) + Cl 2(g) 2ClNO (g) had come to equilibrium, there were 1.70 moles of ClNO in the container. a) Construct a complete I-C-E table for the reaction and find the molar concentrations of NO and Cl 2 at equilibrium. b) Calculate K c for the reaction. ANSWERS 1. For the first reaction, K p = p(Br 2 (g)) [as pure liquids do not appear in the equilibrium constant expression]. Thus the equilibrium constant equals the vapor pressure of the substance, so Br 2 has the larger vapor pressure. 2. a) 2NO (g) + Cl 2(g) 2ClNO (g) Initial moles 4.20 3.40 0 ___ given info Change moles -1.70 -0.85 +1.70 Equilibrium moles 2.50 2.55 1.70 First determine the change in moles of ClNO, then use stoichiometry to find the changes in the moles of NO and Cl 2 . Then the equilibrium amounts of NO and Cl 2 are found.
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