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Unformatted text preview: Name_____________GSI______________ Page 1 of 7 Chemistry 1A, Fall 2007 KEY Midterm Exam III November 13, 2007 (90 min, closed book) N a m e : T A : S I D : S e c t i o n : Please read this first: Write your name and that of your TA on all 8 pages of the exam Test-taking Strategy In order to maximize your score on the exam: Do the questions you know how to do first. Go back and spend more time on the questions you find more challenging. Budget your time carefully -- don't spend too much time on one problem. Show all work for which you want credit and don't forget to include units. Question Page Points Score 1 3 18 2 4 10 3abcd 5 12 3efghi 6 18 4 7 14 5 8 8 Total 80 Useful Equations and constants: G = H - T S H = n H f (products) - n H f (reactants) S = nS (products) - nS (reactants) G = n G f (products) - n G f (reactants) S = k B lnW S = q rev /T E = q + w w = - P ext V G = - RTln K G = G + RTln Q G = - nF = - (RT/nF) lnQ R S T R H K + = 1 ln N = 6.02214 x 10 23 mol-1 T (K) = T (C) + 273.15 F = 96,485 C / mol 1 V = 1 J / C R = 8.31451 J K-1 mol-1 R = 8.20578 x 10-2 L atm K-1 mol Name_____________GSI______________ Page 2 of 7 1) Evaluating H, S, and G. Consider some reactions you have seen in demonstrations in lecture. The change in free energy under standard conditions is given. a. Place checks in the boxes if the reactions match the statements at the top of the columns. Reaction G rxn (kJ) at 25C Products favored Definitely positive S Definitely exothermic I. N 2 O 4 (g) ' 2NO 2 (g) (smog) +4.73 3 II. C 12 H 22 O 11 (s) 12C (s) + 11H 2 O (l) (dehydration of sucrose, black snake) -1062 3 3 III. I 2 (s) ' I 2 (g) +19.33 3 b. Determine the equilibrium constant K P at 25C for Reaction I. Show your work. G = - RTln K 4730 J = - (8.314J/K)(298K)lnK lnK = -1.91, K P = 0.148 c. Consider Reaction II. In the demonstration, Lonnie had to add concentrated H 2 SO 4 to get the reaction started. The diagram of potential energy vs. reaction progress is shown for the reaction without H 2 SO 4 . Draw the diagram for the reaction with H 2 SO 4 . H 2 SO 4 acts as a catalyst, lowering E act d. Consider Reaction III. Suppose you have I 2 (s) in equilibrium with I 2 (g) at the sublimation point of iodine. What is G rxn ?...
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This note was uploaded on 02/08/2010 for the course CHEM 1A taught by Professor Nitsche during the Spring '08 term at University of California, Berkeley.
- Spring '08