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Chapter 13 TAVSS

# Chapter 13 TAVSS - PRACTICE PROBLEMS CHEM 162-2007 EXAM I...

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PRACTICE PROBLEMS CHEM 162-2007 EXAM I CHAPTER 13 - KINETICS RATES, RATE CONSTANTS, REACTION ORDERS, HALF-LIFES CONCEPTS RATES,RATE CONSTANTS, REACTION ORDERS, HALF-LIFES CALCULATIONS REACTION MECHANISMS, ACTIVATION ENERGY & CATALYSTS CONCEPTS REACTION MECH., ACTIVATION ENERGY & CATALYSTS CALCULATIONS E. Tavss, PhD 1

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RATES, RATE CONSTANTS, REACTION ORDERS, HALF-LIFES CONCEPTS 3 Chem 162-2006 Hourly exam I + answers Chapter 12 – Chemical Kinetics Rates, rate constants, reaction orders, half-lives concepts Reaction rates Consider the reaction 4NH 3 (g) + 5O 2 (g) → 4NO(g) + 6H 2 O(g). If the rate of disappearance of O 2 is 0.145 atm/s, what is the rate of appearance of H 2 O? A. 0.145 atm/s B. 0.121 atm/s C. 0.0290 atm/s D. 0.870 atm/s E . 0.174 atm/s The rate of appearance of H 2 O is 6/5 the rate of disappearance of O 2 based on the stoichiometry of the equation. 6/5 x 0.145 atm/s = 0.174 atm/s 4 Chem 162-2006 Hourly exam I + answers Chapter 12 – Chemical Kinetics Rates, rate constants, reaction orders, half-lives concepts Rate laws A graph of 1/[A] vs. time gives a straight line. Which rate law is consistent with this graph? A . r = k[A] 2 B. r = k C. r = k[A] D. r = k[A] -1 E. r = k[A] 3 The graph of 1/[A] vs. time giving a straight line is for a second order reaction: 1/[A] t = kt + 1/[A] o . The rate law for a second order reaction: Rate = k[A] 2 1/[A] t is the Y axis; t is the X axis; k is the slope, and 1/[A] o is the Y-intercept. 2
11 Chem 162-2006 Hourly exam I + answers Chapter 12 – Chemical Kinetics Rates, rate constants, reaction orders, half-lives concepts Reaction order Why can we use the psuedo first order rate constant to solve rate laws with more than one reactant? A. The other reactants disappear so quickly that we can ignore them. B . During the time it takes to use up the limiting reactant, the other reactants have not changed concentration enough to consider. C. The reactant we are considering is present in great excess. D. The reactant we are considering is first order, but the others are not. E. The rate of reaction doesn’t change during the experiment. A. In a pseudo first order reaction, relative to the limiting reactant the other reactants are of such high concentration that they disappear relatively very slowly. B. In a pseudo first order reaction, relative to the limiting reactant the other reactants are of such high concentration that their concentrations essentially don’t change during the reaction, so they can be considered as being constant, and their concentrations are merged into k. C. No. The reactant we are considering is the limiting reactant. D. The reactant we are considering is first order. The order of the others is irrelevant. E. The rate of reaction decreases with time in all first order reactions. 14 Chem 162-2006 Hourly exam I + answers Chapter 12 – Chemical Kinetics Rates, rate constants, reaction orders, half-lives concepts Reaction order A plot of concentration vs. time yields a straight line. The order of the reaction is: A. first B. second C . zero D. half E. third A plot of concentration vs. time yielding a straight line is a zero order reaction.

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Chapter 13 TAVSS - PRACTICE PROBLEMS CHEM 162-2007 EXAM I...

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