103B Exam 1-D

103B Exam 1-D - Exam I master Page 1 Chemistry 103B Exam 1...

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Page 1 Exam I master 4/10/2008 12:19:56 AM http://www.chem.arizona.edu/~kellerp/exams/Exam1/Exam1Dan/Exam1Dan.htm Chemistry 103B Exam 1 Answer Key Form D 1. (2) When a chemical reaction has reached equilibrium (a) the reaction quotient Q has reached a minimum (b) the concentrations of the reactants have become equal to the concentrations of the products (c) the concentrations of the reactants have all reached 0 mol/L (d) the concentrations of reactants and products have reached constant values (e) the forward and reverse reactions have both stopped 2. (2) Shown below are the elementary steps in the mechanism of a gas phase reaction BC(g) B(g) + C(g) [slow] B(g) + A(g) AB(g) [fast] C(g) + A(g) AC(g) [fast] AB(g) + AC(g) A 2 BC(g) [fast] If more molecules of A are added (a) the rate will increase (b) the rate willbe unchanged (c) the rate will decrease (d) the activation energy will decrease (e) the activation energy will increase 3. (2) In a period of 300s the concentration of BC(g) in the above reaction dropped from0.500mol/L to 0.250mol/L. How long would it take for the concentration of BCto drop from0.250to 0.125mol/L? (a) 300s (b) 710s (c) 655s (d) 175s (e) none of these The mechanism clearly shows the slow step is unimolecular. For such reactions , the half-lifeis constant . It took 300s for the concentration of BCto drop from0.500to 0.250mol/L. It willtake 300s for it to drop from0.250mol/L to half that value.
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Page 2 Exam I master 4/10/2008 12:19:56 AM http://www.chem.arizona.edu/~kellerp/exams/Exam1/Exam1Dan/Exam1Dan.htm 4. (2) This reaction is exothermic: CO(g) + 2 H 2 (g) CH 3 OH(g). A reaction vessel contains these compounds in equilibrium. What willbe the effect of adding more CO(g) to the vessel ? (a) the concentration of CH 3 OH willdrop (b) the concentration of H 2 willdrop (c) the concentration of H 2 willincrease (d) the temperature will decrease (e) none of these 5. (2) This reaction is exothermic: CO(g) + 2 H 2 (g) CH 3 OH(g). A reaction vessel contains these compounds in equilibrium. What willbe the effect of lowering the temperature? (a) the
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This test prep was uploaded on 04/10/2008 for the course CHEM 103B taught by Professor Keller during the Spring '08 term at Arizona.

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103B Exam 1-D - Exam I master Page 1 Chemistry 103B Exam 1...

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