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Chem 162-2011 Chapter 13A-Some Kinetics practice problems

Chem 162-2011 Chapter 13A-Some Kinetics practice problems -...

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PRACTICE PROBLEMS CHEM 162-2010 EXAM I CHAPTER 13A - KINETICS RATES, RATE CONSTANTS, REACTION ORDERS, HALF-LIVES CONCEPTS RATES,RATE CONSTANTS, REACTION ORDERS, HALF-LIVES CALCULATIONS E. Tavss, PhD 1

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RATES, RATE CONSTANTS, REACTION ORDERS, HALF- LIVES CONCEPTS Chem 162-2007 Final exam + answers Chapter 13 – Kinetics Rates, rate constants, reaction orders, half-lives concepts 2
11 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 0 100 200 300 400 500 Time (s) Concentration (M The graph above represents data taken for the reaction: 2NO 2 (g) 2NO(g) + O 2 (g) In the experiment, 0.010 mol of NO 2 (g) is introduced into a 1.00 L rigid flask held at constant temperature. Which conclusions can be made from this graph? X. [ ] [ ] t O t NO = - 2 2 2 1 Y. The forward rate of the reaction equals zero at t = 500 seconds Z. The forward rate of the reaction is greater than the reverse rate of the reaction at t = 100 seconds A. X, Y, and Z B . X, Z only C. X, Y only D. Y, Z only E. Y only X. True. This is saying that ½ the rate of disappearance of NO 2 = the rate of appearance of O 2 . Y. False. There is always a dynamic equilibrium. There is always a finite forward rate and a finite reverse rate. Neither one is ever equal to zero. At equilibrium (e.g., 500 sec), macroscopically we see no change, which is what is observed in the graph, but this is because the forward rate equals the reverse rate, not because the forward rate or the reverse rate equals zero. Z. True. Since the reaction is going forward (i.e., the concentration of reactant is decreasing while the concentrations of products are increasing), then the forward rate must be greater than the reverse rate. 3 NO 2 NO O 2

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23 Chem 162-2007 Final exam + answers Chapter 13 – Kinetics Rates, rate constants, reaction orders, half-lives concepts A chemical system is at equilibrium A. when the concentration of reactants and products are equal. B. when all of the reactants have been used up. C. when the rate of the forward reaction becomes zero. D. when the rates of the forward reaction and the reverse reaction are both zero. E . when the rates of the forward reaction and the reverse reaction are equal. A. False. A system is only at equilibrium when the rate of the forward reaction = the rate of the reverse reaction, i.e., if A B, k f [A] = k r [B]. Since k f is rarely equal to k r , then [A] is rarely equal to [B] at equilibrium. B. False. The position of equilibrium depends on the G of the reaction. For example, if G is positive, then at equilibrium there will be more reactant than product. G would have to be infinitely negative to have a situation in which all of the reactants would be used up at equilibrium. C. False. The rate of the forward reaction is never equal to zero, except at the temperature of absolute zero. There is always a finite forward reaction and a finite reverse reaction.
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Chem 162-2011 Chapter 13A-Some Kinetics practice problems -...

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