chem1A-Fall08-mt2-Stacy-soln

chem1A-Fall08-mt2-Stacy-soln - Name_GSI_ Chemistry 1A, Fall...

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Name_____________GSI______________ Page 1 of 8 Chemistry 1A, Fall 2008 KEY Midterm Exam #2 October 14, 2008 (90 min, closed book) Name:____________________ _____ SID:___________________________________ GSI Name:________________ The test consists of 4 short answer questions and 11 multiple choice questions. Put your written answers in the boxes provided. Answers outside the boxes may not be considered in grading. Show your work to receive the maximum credit possible. Write your name on every page of the exam. Page Points Score Question A 2 15 Question B(i-vii) 3 17 Question B (viii-ix) Question C (bonus) 4 6 Question D 5 27 Question E 6 13 Question F and G (multiple choice) 7-8 24 Total 100 Useful Equations and Constants: pH = - log[H 3 O + ] pX = - log X ] [ ] [ log HA A pK pH a + = N 0 = 6.02×10 23 1/mol Strong acids and bases: HCl LiOH HNO 3 NaOH H 2 SO 4 KOH HClO 4 HBr HI
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Name_____________GSI______________ Page 2 of 8 0 1 2 3 4 5 Time (sec) Number (moles) A) Gas Phase Equilibria Consider the reaction between ethylene, C 2 H 4 , and hydrogen, H 2 to form ethane, C 2 H 6 . C 2 H 4 (g) + H 2 (g) ' C 2 H 6 (g) The progress of a reaction between 5.0 moles of C 2 H 4 (g) and 5.0 moles of H 2 (g) is shown in the graph below. i. What is the equilibrium constant for the reaction? Assume the reaction container is 1.0 liter. Show your work. Imagine that the same reaction starts with the ethylene, C 2 H 4 (g), and hydrogen, H 2 (g) reactants only. This reaction mixture results in the moles listed below at equilibrium . moles ethylene, C 2 H 4 (g) at equilibrium = 1.0 moles moles hydrogen, H 2 (g) at equilibrium = 0.50 moles moles ethane, C 2 H 6 (g) at equilibrium = 2.0 moles ii. How many moles of ethylene, C 2 H 4 (g), and hydrogen, H 2 (g) were present at the start of the reaction? C 2 H 4 ( g ) + H 2 ( g ) ' C 2 H 6 ( g ) Initial X Y 0 Change -2.0 -2.0 +2.0 Equilibrium 1.0 0.50 2.0 X – 2.0 = 1.0, X = moles of C 2 H 4 ( g ) = 3.0 moles Y – 2.0 = 0.50, Y = moles of H 2 ( g ) = 2.5 moles Imagine that the same reaction begins with 5.0 moles of ethane, C 2 H 6 (g) and no reactants. iii. moles C 2 H 6 + moles C 2 H 4 = ____5.0 moles _____ iv. moles C 2 H 6 + moles H 2 = ______5.0 moles ____ v. Draw a graph showing the progress of the reaction. Label the curves showing all 3 molecules. may have reasoned it out or done ICE table, if ICE then 4x 2 – x – 5 = 0 and x = 1 = moles C 2 H 4 and H 2 moles of C 2 H 6 (g) moles of C 2 H 4 (g) or H 2 0 1 2 3 4 5 Time (sec) initial equilibrium ( ) () () 0 . 4 0 . 1 0 . 1 0 . 4 ] ][ [ ] [ 2 4 2 6 2 = = = M M M H H C H C K eq moles of C 2 H 4 (g) or H 2 moles of C 2 H 6 (g)
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Name_____________GSI______________ Page 3 of 8 B) Heterogeneous Equilibria The common light bulb has a thin wire made of tungsten, W, in a glass bulb with all the air removed. The tungsten wire glows when it is heated with an electric current. If the tungsten wire breaks, the light bulb no longer lights. i.
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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.

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chem1A-Fall08-mt2-Stacy-soln - Name_GSI_ Chemistry 1A, Fall...

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