CHEM126 – CHAPTER 13 – BASIC HOMEWORK / KINETICS II

CHAPTER 13 BASIC HOMEWORK

KINETICS II

Question 1

For the first-order rate of reaction A –> B + C, what is the concentration of A (in M) after 46.0 s if [A]o = 0.40 M and k = 0.050 s-1?

Correct

Explanation

Here we are told that the reaction rate is first order. Use the first order integrated rate equation (can also be found on your ACS periodic table) and the given values to find [A].
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Question 2

For a first-order reaction, the initial reactant concentration is 0.789 M. After 64.7 min, the concentration is 0.520 M. What is k in min-1?

Correct

Explanation

Use first order integrated rate equation and given values to solve for k.
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Question 3

For a first order reaction, the initial reactant concentration, [A]o, is 0.94 M. After 14.4 s, the concentration is 0.67 M. What is [A] after 82 s? Hint given in feedback
Correct

Explanation

 Do the problem in 2 steps. First find k and then the new concentration. Both steps are done using first order integrated rate equation.
Step 1:
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Step 2:
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Question 4

Suppose the rate of reaction is second order for A → B + C. What is the concentration of A (in M) after 93.0 s if [A]o = 0.70 M and k = 0.034 M-1s-1 Help: Second order rate of reaction
Correct

Explanation

Use the second order integrated rate equation (can also be found on your ACS periodic table) and the given values to find [A].
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Question 5

For a second-order reaction, the initial reactant concentration is 0.90 M. After 14.8 min, the concentration is 0.28 M. What is k in M-1min-1? Help: Second order rate of reaction and k
Correct

Explanation

 Use second order integrated rate equation and given values to solve for k.
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Question 6

For a second order reaction, the initial reactant concentration, [A]o, is 0.94 M. After 11.7 s, the concentration is 0.59 M. What is [A] after 80 s? Hint given in feedback
Correct

Explanation

 Solve the problem in 2 steps. First fine k (like earlier problems) and then use the second order integrated rate equation to get the concentration.
Step 1:
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Step 2:
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Question 7

For the zero-order rate of reaction A → B + C, what is the concentration of A (in M) after 36.0 s if [A]o = 0.80 M and k = 0.010 Ms-1?

Correct

Explanation

 Use zero order integrated rate equation and given values to solve for [A].
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Question 8

For a certain reaction, when the natural log of the reactant concentration is plotted against the time in seconds a straight line is obtained. What is the reaction order? Help: Comparison of rate laws
Select one:
 Correct

Explanation

Concise explanation and comparison of orders and plots can be found here. It will serve you well to remember which graphs are linear for which orders, as this topic is likely to be on the final exam, not to mention your upcoming common exam! 😉 . Zero order: linear for [A] v. time First order: linear for ln[A] v. time Second order: linear for 1/[A] v. time

Question 9

For the above reaction, the slope is -0.016. What are the units of the slope and what is k? Note, logs are unitless! Additional hint given in feedback.

Select one or more:

 Correct
 Correct

Explanation

The slope is the change in y divided by the change in x. So, the units are the units of y divided by the units of x.

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This example plot may help you understand why k is positive

Question 10

For the reaction D → A + C when 1/[D] is plotted versus the time in seconds, a straight line is obtained whose slope is 0.017 M-1s-1. What is the concentration of D (in M) after 95.0 s if [D]o = 0.80 M? Hint given in feedback
Correct

Explanation

First use the information given about the plot to determine the order of the reaction and k. Zero order: linear for [A] v. time First order: linear for ln[A] v. time Second order: linear for 1/[A] v. time The fact that the plot is linear for 1/[D] v. time tells us that we have a second order reaction. Next use appropriate integrated rate equation to determine the concentration:
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Question 11

For the reaction A → B + C when [A] is plotted versus the time in minutes a straight line is obtained whose slope is -0.011 M/min. What is the concentration of A (in M) after 10.00 min if [A]o = 0.70 M?
Correct

Explanation

 Same as above.
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Question 12

For the reaction A → B + C, when the natural log of [A] is plotted versus the time in seconds a straight line is obtained whose slope is -0.042 s-1. What is the concentration of A (in M) after 49.0 s if [A]o = 0.90 M?
Correct

Explanation

 Same as above.
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