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CH 302 - [McCord] [Spring 2010] - Test 4

# CH 302 - [McCord] [Spring 2010] - Test 4 - Version 058 Exam...

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Version 058 – Exam 4 – Mccord – (52450) 1 This print-out should have 30 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points If an individual step in a reaction mechanism is bimolecular, is that step necessarily of sec- ond order? 1. Yes correct 2. No Explanation: The number of reactant molecules in an elementary step of a mechanism is the order of that step. 002 10.0 points You need that 2 in the calculation. For the reaction 2 A B the concentration of [A] after 15 hours is 0.15 M. How much of compound [A] was initially present if k = 2 . 16 × 10 7 M/s? 1. 1 . 617 × 10 1 M 2. 7 . 32 × 10 2 M 3. 1 . 733 × 10 1 M correct 4. 1 . 504 × 10 1 M 5. 1 . 535 × 10 1 M Explanation: 003 10.0 points While electroplating a spoon with silver (molar mass = 107.9 g/mol) from an Ag 2+ so- lution, 19 . 3 × 10 3 C of charge is used. By how much has the mass of the spoon increased? 1. 5.39 g 2. 10.79 g correct 3. 107.9 g 4. 53.9 g 5. 21.58 g 6. 0 g Explanation: This is a 2 electron process. g = Q(molar mass) nF = (19 . 3 × 10 3 C)(107 . 9 g / mol) (2)(9 . 65 × 10 4 C / mol) = 10 . 79 g 004 10.0 points What is the potential in an electrolysis cell formed from the two half reactions below if the sodium ion concentration is 10 3 M and the aluminum ion concentration is 1M? Half reaction E Na + -→ Na - 2 . 7 V Al 3+ -→ Al - 1 . 7 V 1. -1.18V correct 2. -1.0V 3. -0.82V 4. 1.18V 5. 1.0V 6. 0.82V Explanation: E = - 1 . 0 V E cell = E cell - 0 . 05916 N e log Q = - 1 . 0 - 0 . 05916 3 log [Al 3+ ] [Na + ] 3 = - 1 . 0 - 0 . 05916 3 × 9 = - 1 . 18

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Version 058 – Exam 4 – Mccord – (52450) 2 005 10.0 points Which statement best describes the action of a catalyst? 1. It releases activation energy for a chemical reaction. 2. It changes the reactants necessary for a chemical reaction. 3. It raises the activation energy for a chem- ical reaction. 4. It lowers the activation energy for a chem- ical reaction. correct Explanation: 006 10.0 points Consider the data below: [CH 4 ] [O 2 ] initial rate M M M · s 1 Exp 1 0 . 5 1 . 3 2 . 5 × 10 3 Exp 2 0 . 5 2 . 6 1 . 0 × 10 2 Exp 3 1 . 0 1 . 3 5 . 0 × 10 3 Which of the following is a correct rate law for the reaction? 1. k [CH 4 ] 1 [O 2 ] 2 2. k [CH 4 ][O 2 ] 2 correct 3. k [CH 4 ] 4. k [CH 4 ] 1 [O 2 ] 5. k [CH 4 ][O 2 ] Explanation: rate 1 rate 2 = [O 2 ] 1 [O 2 ] 2 2 . 5 × 10 3 1 . 0 × 10 2 = parenleftbigg 1 . 3 2 . 6 parenrightbigg x x = 2 rate 3 rate 1 = [CH 4 ] 3 [CH 4 ] 1 5 . 0 × 10 3 2 . 5 × 10 3 = parenleftbigg 1 . 0 0 . 5 parenrightbigg y y = 1 007 10.0 points The reaction 2 A + B 2 C has a negative Δ H r ; a possible mechanism for this reaction is (1) 2 A D rapid equilibrium, K (2) D + B 2 C slow, k What is the reaction profile diagram for this reaction? 1. reactants products Energy -→ Reaction progress -→ 2. reactants products Energy -→ Reaction progress -→
Version 058 – Exam 4 – Mccord – (52450) 3 3. reactants products Energy -→ Reaction progress -→ 4. reactants products Energy -→ Reaction progress -→ 5.

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CH 302 - [McCord] [Spring 2010] - Test 4 - Version 058 Exam...

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