#Chem 162-2008 3rd week homework

#Chem 162-2008 3rd week homework - Hill Petrucci Chapter 13...

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Hill & Petrucci Chapter 13 Homework Problems Rate of Reaction and Reaction Order 23. The initial concentration of H 2 O 2 is 0.2546 M, and the initial rate of reaction is 9.32 x 10 -4 Ms -1 . What will be [H 2 O 2 ] at t = 35s? Reaction rate = -(C 2 -C 1 )/(t 2 -t 1 ) 9.32 x 10 -4 Ms -1 = -(C 2 – 0.2546M)/(35s – 0s) X = 0.2220 M H 2 O 2 25. In the reaction A + 2B → C + 3D, the rate of disappearance of B is -6.2 x 10 -4 Ms -1 . What is (a) the rate of disappearance of A? (b) The rate of formation of D? (c) The general rate of reaction as described on page 530? (a) The rate of disappearance of A is ½ the rate of disappearance of B. Therefore, the rate of disappearance of A is 3.1 x 10 -4 Ms -1 . (The rate of disappearance of B is incorrectly stated as -6.2 x 10 -4 Ms -1 . If the rate of disappearance of B were -6.2 x 10 -4 Ms -1 , then that would mean that the rate of appearance of b was +6.2 x 10 -4 Ms -1 , which would mean that the concentration of B was increasing, which is impossible since B is a reactant. (b) The rate of formation of D is 3/2 the rate of disappearance of B. Therefore it is 9.3 x 10 -4 Ms -1 . (c) The general rate of reaction the rate of appearance or disappearance of any of the reactants or products, but normalized to a coefficient of 1. Since A already has a coefficient of 1 in the stoichiometry equation, then the general rate is the same as the rate of disappearance of A, which is 3.1 x 10 -4 Ms -1 . 27. For the reaction A → products, a graph of [A] versus time is a curve. What can be concluded about the order of this reaction? Since only a zero order reaction provides a straight line when the concentration of A is plotted against time, then we can conclude that the reaction of A to form products is not a zero order reaction. 29. For the reaction 2A → B + C, at least one of the following statements is true. Label the statements as true or false, and explain your reasoning. (a) The half-life of this reaction can be determined with the expression t 1/2 = 1/k[A] o , where k is the rate constant and [A] o is the initial concentration of A. (b) The rate at which B is produced is not the same as the rate at which A is consumed. (a) Maybe true, maybe false. This would be true only if this was a second order reaction. However, we have no way of knowing the order of this reaction. I disagree with the Solutions Manual answer. There is not enough information provided to know if this is true or false. This could be true if it was a second order reaction. (b) True. The rate at which B is produced is ½ the rate at which A is consumed. 1
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31. The rate of the following reaction in aqueous solution is monitored by measuring the rate of formation of I 3 - . Data obtained are listed in the table. S 2 O 8 2- + 3I - → 2SO 4 2- + I 3 - Experiment [S 2 O 8 2- ],M [I - ],M Initial Rate, Ms -1 1 0.038 0.060 1.4 x 10 -5 2 0.076 0.060 2.8 x 10 -5 3 0.076 0.120 5.6 x 10 -5 (a) Determine the order of the reaction with respect to S 2 O 8 2- , with respect to I - , and overall.
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