115b_exam2key_08

115b_exam2key_08 - Chem 115b Spring 2008 Exam 2 February...

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Chem 115b KEY Spring 2008 Print Name: Last First Exam 2 Last 3 digits of Student ID # February 21, 2008 TA's Name P r o f e s s o r s R e i s l e r / K r y l o v M a j o r Questions Points Score Grader 1 16 2 12 3 12 4 13 5 12 6 15 7 20 Total 100 INSTRUCTIONS 1. YOU MUST SHOW YOUR WORK TO RECEIVE CREDIT. 2. If necessary, please continue your solutions on the back of the preceding page (facing you). 3. YOU MUST USE BLACK INK TO BE ABLE TO REQUEST A REGRADE 4. Please read each question carefully before you write your answer. 5. There are 7 questions on 8 pages. ± Please Sign Below: I certify that I have observed all the rules of Academic Integrity while taking this examination. Signature:
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1 1. (16 points) Circle the correct letter answer in the multiple choice questions (a) (3 points) Which of the following statements is true? A. The concentration of the products equals that of reactants and is constant at equilibrium. B. Catalysts are an effective means of changing the position of the equilibrium. X C. When two opposing processes are proceeding at identical rates, the system is at equilibrium. D. An endothermic reaction shifts toward reactants when heat is added to the reaction. E. None of these statements is true. (b) (3 pts) When cobalt chloride is added to pure water, the Co 2+ ions hydrate. The hydrated form then reacts with the Cl - ions to set up the equilibrium. Co(H 2 O) 6 2+ + 4Cl - CoCl 4 2- + 6H 2 O (pink) (blue) How would the color change when hydrochloric acid is added? X A. It would become more blue. B. It would become more pink. C. There will be no change in color (c) (3 pts) The equilibrium reaction H 2 O (g) + Cl 2 O (g) 2HOCl (g) is known to be an elementary reaction. Write an expression for K in terms of the rate constants for these reactions. At equlibrium: k 1 [H 2 O][Cl 2 O] = k -1 [HOCl] 2 -> K = [HOCl] 2 /[H 2 O][Cl 2 O] = k 1 / k -1 (d) For the reaction: 2AsH 3 (g) 2As(s) + 3H 2 (g) (i) (2 pt) Write the expression for K p (ii) (3 pts ) Write the expression for K c in terms of K p p = (n/V)RT = [C]RT -> [C] = p/RT (iii) (2 pts) Write an expression for K' p for the reaction: As(s) + (3/2)H 2 (g)
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This note was uploaded on 07/14/2008 for the course CHEM 115BL taught by Professor Qin,reisler during the Spring '08 term at USC.

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115b_exam2key_08 - Chem 115b Spring 2008 Exam 2 February...

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