Ex1_S07_ans - Name_A Key Problem Session_All Chem 114 Exam...

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Name ______A. Key___________ Problem Session _All__ Chem 114 Exam 1 Dr. A. H. Martin Total Points = 100 February 9, 2007 Complete calculations must be shown for all problems to receive full credit. (6) 1. Consider the reaction 3A + 2B C + 4D If the rate of formation of D is ∆[D]/∆t, write the rate of reaction expressed in terms of A, B, and C.  = - 4 D [A] 3 D t   =   - 2 D [B] D t =   4 D [C] D t (6) 2. Answer the following based on the mechanism below: A + C X (fast) X + C Y (slow) Y + B Z + A (fast) Z + C P (fast) a) Give the overall equation for the reaction. B + 2C P b) Give the rate law for the reaction. rate = k[A][C] 2 c) What is (are) the catalyst(s) in the reaction? ____A_________________ (10) 3. Consider the reaction 2A + B 2C + D. A kinetic study of this reaction was conducted with the initial concentration of a equal to 0.20 M. A graph of the ln [A] versus time in seconds for this reaction was linear with a slope of -55 sec -1 . a) What is the value of k for this reaction? 55 sec -1 b) What is the rate law for the reaction? rate =55[A] c) What is the half life for the reaction? _t 1/2 = 0.963/k = 0.693/55 = 0.0126 sec_____ d) What is the concentration of A left after 2 half lives? 0.05 M e) Assuming no volume change, what is the concentration of D produce after 2 half lives? ____0.075 M______ (8) 4. Answer the following based on the diagram below. a) Give the letter for the activation energy of the forward reaction. _B__ b) Is the forward reaction exothermic or endothermic? _Exothermic__ c) Which letter indicates the energy change of the reaction? ___F____ d) Which the letter that indicates the transition state. _____C______ reaction coordinate energy A C B D E F
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Chem 114 Exam 1 Page 2 (18) 5. Predict the following and justify your prediction. a) Does lowering the activation energy of a reaction, increase or decrease the rate of the reaction? Increase – with a lower activation energy a greater percentage of the collisions will have enough energy for the reaction to take place. This will result in an increase in the reaction rate b) If the rate law for a reaction is rate =k[C] 2 , will the first half-life or the second half-life of the reaction be longer? 2 nd half-life – for a second order reaction the initial concentration is included in the half-life term (t 1/2 = 1/k[C] 0 ). Since the initial concentration at the start of the second half-life is half of that at the start of the reaction, the second half-life will be twice as long as the first half life. c)
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This note was uploaded on 04/03/2008 for the course CHEM 114 taught by Professor Martin during the Spring '08 term at Moravian.

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Ex1_S07_ans - Name_A Key Problem Session_All Chem 114 Exam...

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