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5 - Elbel Brittany Homework 5 Due noon Inst J A Holcombe...

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Elbel, Brittany – Homework 5 – Due: Feb 20 2006, noon – Inst: J A Holcombe 1 This print-out should have 24 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. 001 (part 1 of 1) 10 points A certain reaction has a K c = 9 . 0 at 35 C. A(g) + B(g) * ) 2 C(g) We have a mixture in which [A] = 2 M, [B] = 4 M, and [C] = 1.5 M. Which of the following is true of the mix- ture? 1. The reaction will go to the right. correct 2. More A and B will be formed to achieve equilibrium. 3. The reaction will go to the left. 4. The mixture is at equilibrium. Explanation: K c = 9 . 0 [A] = 2 M [B] = 4 M [C] = 1 . 5 M Q = [C] 2 [A] [B] = (1 . 5 M) 2 (2 M) (4 M) = 0 . 28 < K c = 9 . 0 Therefore, equilibrium will shift to the right. 002 (part 1 of 1) 10 points At 990 C, K c is 1.6 for the reaction CO 2 (g) + H 2 (g) * ) H 2 O(g) + CO(g) If 4.0 mol of CO, 3.0 mol of H 2 O, 2.0 mol of H 2 , and 1.0 mol of CO 2 are placed in a 5.0 liter container and allowed to reach equilibrium at 990 C, which response includes all of the following statements that are correct, and no others? I) The concentration of H 2 will be greater than 0.40 mol/L. II) The concentration of H 2 O will be less than 0.60 mol/L. III) The concentration of CO will be less than 0.80 mol/L. IV) The concentration of CO 2 will be greater than 0.20 mol/L. 1. I, II, III, and IV correct 2. I and IV only 3. I and II only 4. III only 5. I, II, and IV only Explanation: [H 2 O] ini = 3 . 0 mol 5 . 0 L = 0 . 6 M [CO] ini = 4 . 0 mol 5 . 0 L = 0 . 8 M [CO 2 ] ini = 1 . 0 mol 5 . 0 L = 0 . 2 M [H 2 ] ini = 2 . 0 mol 5 . 0 L = 0 . 4 M Q = [H 2 O] [CO] [CO 2 ] [H 2 ] = (0 . 6 M) (0 . 8 M) (0 . 2 M) (0 . 4 M) = 6 > K c = 1 . 6 Therefore equilibrium will shift to the left, in- creasing [CO 2 ] and [H 2 ] and decreasing [H 2 O] and [CO]. 003 (part 1 of 1) 10 points CS 2 and Cl 2 react according to the following equation CS 2 (g) + 3 Cl 2 (g) * ) S 2 Cl 2 (g) + CCl 4 (g) . When 1.0 mole of CS 2 and 3.00 moles of Cl 2 are placed in a 2.00 liter container and allowed to come to equilibrium, the mixture is found to contain 0.25 moles of CCl 4 . What is the amount of Cl 2 at equilibrium? 1. 0.25 mol Cl 2 2. 0.75 mol Cl 2
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Elbel, Brittany – Homework 5 – Due: Feb 20 2006, noon – Inst: J A Holcombe 2 3. 2.25 mol Cl 2 correct 4. 0.50 mol Cl 2 5. 2.75 mol Cl 2 Explanation: Initially, [CS 2 ] = 1 mol 2 L = 0 . 5 M [Cl 2 ] = 3 mol 2 L = 1 . 5 M CS 2 (g)+ 3 Cl 2 (g) * ) S 2 Cl 2 (g)+ CCl 4 (g) 0.5 M 1.5 M 0 M 0 M - x M - 3 x M x M x M 0 . 5 - x 1 . 50 - 3 x x x At equilibrium, [CCl 4 ] = x = 0 . 25 mol 2 . 0 L = 0 . 125 M mol Cl 2 = [1 . 50 M - 3(0 . 125 M)](2 . 00 L) = 2 . 25 mol 004 (part 1 of 3) 10 points Consider the reaction HCHO(g) * ) H 2 (g) + CO(g) 1.0 mol of HCHO, 1.0 mol of H 2 and 1.0 mol of CO exist in equilibrium in a 2.0 L reaction vessel at 600 C. a) Determine the value of the equilibrium constant K c for this system. 1. 2.0 2. 1.0 3. K c cannot be determined for gaseous equilibria. 4. 0.50 correct 5. Some other value Explanation: The expression for K c here is K c = [H 2 ] [CO] [HCHO] , so we need to know the equilibrium concen- trations of each of the species. Since each is 1 . 0 mol 2 . 0 L = 0 . 50 M, then K c = [0 . 50] [0 . 50] [0 . 50] = 0.50 005 (part 2 of 3) 10 points 2.0 moles of HCHO and 1.0 mol of CO are then added to this system.
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