CHEM126 - CHAPTER 13 - BASIC HOMEWORK / KINETICS I

CHAPTER 13 BASIC HOMEWORK

KINETICS I

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Question 1

For the reaction: 3BrO^–(aq) –> BrO₃^–(aq) + 2Br^–(aq) [BrO^–]_initial is 0.60 M. 70 seconds later [BrO^–] is 0.12 M. What is the rate of change of [BrO^–] in M/s? (The brackets, [ ], indicate concentration, that is, molarity (M) or moles/liter.)

Help: Rate of change defined

Answer:

Explanation

Notice that the rate of change of a reactant is negative because it is being used up.

CHEM126 - CHAPTER 13 - BASIC HOMEWORK / KINETICS I 1

Question 2

Under a different set of conditions, the initial concentration of Br^– is 0.00 M. 81 seconds later it is 0.82 M. What is the rate of change of Br^– in M/s?

Answer:

Explanation

Notice that the rate of change of a product is positive because it is being produced.

CHEM126 - CHAPTER 13 - BASIC HOMEWORK / KINETICS I 2

Question 3

Under a different set of conditions, the initial concentration of BrO₃^– is 0.23 M. 14 seconds later it is 0.83 M. What is the rate of change of BrO₃^– in M/s?

Answer:

Explanation

Notice that the rate of change of a product is positive because it is being produced.

Question 4

Still for the reaction: 3BrO^–(aq) –> BrO₃^–(aq) + 2Br^–(aq), what is the rate of reaction in M/s, if Δ[BrO^–]/Δt = -0.074 M/s? Help: Rate of reaction

Answer:

Explanation

We are given the rate of change of [BrO^–]. Because the chemical equation has 3 moles of BrO^–, we must divide by 3 to get the rate of reaction.

CHEM126 - CHAPTER 13 - BASIC HOMEWORK / KINETICS I 3

Note that the rate of reaction is always positive.

Question 5

Under a different set of conditions Δ[BrO₃^– ]/Δt = 0.029 M/s. What is the rate of reaction in M/s?

Answer:

Explanation

In this case, the coefficient of [BrO₃^–] is 1. Therefore:

Δ[BrO₃^– ]/Δt = Rate of reaction = .029

Note that the rate of reaction is always positive.

Question 6

Under a different set of conditions Δ[Br^–]/Δt = 0.035 M/s. What is the rate of reaction in M/s?

Answer:

Explanation

CHEM126 - CHAPTER 13 - BASIC HOMEWORK / KINETICS I 4

Note that the rate of reaction is always positive.

Question 7

If Δ[BrO₃^– ]/Δt = 0.010 M/s. What is Δ[Br^–]/Δt in M/s? Reminder, the rate of change [BrO₃^– ] is Δ[BrO₃^– ]/Δt. Help: Rate of change of reactants and products

Answer:

Explanation

Once again, take a look at the coefficients (molar amounts) in the chemical reaction to help you solve this one. If Δ[BrO₃^– ]/Δt = 0.010 M/s, then Δ[Br^–]/Δt = 0.010 x 2 = 0.020

Question 8

If Δ[BrO₃^–]/Δt = 0.024 M/s. What is [BrO^–]/Δt in M/s?

Answer:

Explanation

Note that [BrO^–]/Δt is negative, because BrO^– is a reactant.

CHEM126 - CHAPTER 13 - BASIC HOMEWORK / KINETICS I 5

Question 9

The rate of change of [B] is -0.243 M/min. What is the rate of reaction for the following reaction in M/min? 2A + 5B → 3C + 7D

Answer:

Explanation

(-.0243) / -5 = .0486

Question 10

Under a different set of conditions, the rate of change of [C] is 0.162 M/min. What is the rate of change of [D] in M/min? Hint given in feedback

Answer:

Explanation

Hint, if a = b and b = c, then a = c. Specifically, what is the rate of reaction using [C] and what is the rate using [D]? Set the rate using [C] = the rate using [D] and solve for the rate of change of [D].

CHEM126 - CHAPTER 13 - BASIC HOMEWORK / KINETICS I 6

Question 11

If the rate of change of [C] is 0.149 M/min. What is the rate of change of [A] in M/s? Hint given in feedback’

Answer:

Explanation

Hint. What is the rate of reaction using [C] and what is the rate using [A]? Set the rate using [C] = the rate using [A] and solve for the rate of change of [A]. Check: is the rate of change of [A] positive or negative? Finally, units for rate of change of [A] are M/s not M/min. (1/min) = (1/min)(1 min/60 s).

CHEM126 - CHAPTER 13 - BASIC HOMEWORK / KINETICS I 7

Question 12

For the reaction 2A +3B → C + 4D The rate of reaction = k[A]^0.5[B]² Which of the following statements are true?

Help: Order of reaction

Select one or more:

a. The reaction rate with respect to A is 0 order.

b. The reaction rate with respect to A is one-half order. Correct

c. The reaction rate with respect to B is first order.

d. The reaction rate with respect to B is second order. Correct

e. The overall reaction rate order is 1.

f. The overall reaction rate order is 2.

g. The overall reaction rate order is 2.5. Correct

Explanation

To determine order of a particular reactant, look at its superscript. To determine overall reaction rate order, find the sum of superscripts.

Question 13

For a new reaction with reactant “A”, suppose the rate of reaction is 0.04 M/sec when [A] = 0.23 M. The concentration of A is doubled to 0.46 M. Match the rate of reaction to the reaction order.

Help: Rate of reaction and order

Rate is still 0.04 M/s	Answer 1
Rate is 0.04 x 2^0.5 = 0.057 M/s	Answer 2
Rate is 0.04 x 2¹ = 0.08 M/s	Answer 3
Rate is 0.04 x 2² = 0.16 M/s	Answer 4

Explanation

Here we are essentially comparing the relative amount of change in concentration (∆[A]) to the relative amount of change in reaction rate in order to find the reaction order. Note that K (rate constant) cancels out in each equation.

Answer 1:

CHEM126 - CHAPTER 13 - BASIC HOMEWORK / KINETICS I 8

Answer 2:

CHEM126 - CHAPTER 13 - BASIC HOMEWORK / KINETICS I 9

Answer 3:

CHEM126 - CHAPTER 13 - BASIC HOMEWORK / KINETICS I 10

Answer 4:

CHEM126 - CHAPTER 13 - BASIC HOMEWORK / KINETICS I 11

Question 14

For the reaction 2NO₂(g) → 2NO(g) + O₂(g) the following experimental data was obtained for the rate:

Run	[NO₂] (M)	Rate (M/s)
1	0.16	0.27
2	0.32	1.08
3	0.64	4.32

What is the reaction rate order? Hint given in feedback.

Select one:

a. zero-order

b. one half-order

c. first-order

d. second order Correct

Explanation

Hint, what happens to the reaction rate when the reactant concentration is doubled?

CHEM126 - CHAPTER 13 - BASIC HOMEWORK / KINETICS I 12

Question 15

What is k? Hint given in feedback

Answer:

Explanation

Substitute the data from one of the runs into the appropriate equation and solve for k. For zero-order, the rate of reaction = k[NO₂]⁰ = k. For first-order, the rate of reaction = k[NO₂]¹ For one half-order, the rate of reaction = k[NO₂]^0.5 For second-order, the rate of reaction = k[NO₂]²

CHEM126 - CHAPTER 13 - BASIC HOMEWORK / KINETICS I 13

Question 16

What are the units of k?

Help: Finding units of k

Select one:

a. M/s

b. M^0.5/s

c. 1/s or s^-1

d. 1/(Ms) or M^-1s^-1 Correct

e. unitless

Explanation

Khan Academy – How to find units of rate constant k

CHEM126 - CHAPTER 13 - BASIC HOMEWORK / KINETICS I 14

Question 17

What is the rate when [NO₂] = 0.121 M? Hint given in feedback

Answer:

Explanation

Use the rate equation for the correct order with the k that you determined.

CHEM126 - CHAPTER 13 - BASIC HOMEWORK / KINETICS I 15

Question 18

For the reaction 2H₂O₂(aq) → 2H₂O(l) + O₂(g) the following experimental data was obtained for the rate:

Run	[H₂O₂] (M)	Rate (M/s)
1	0.043	0.19
2	0.065	0.29
3	0.086	0.38

What is the reaction rate order? Hint given in feedback

Select one:

a. zero-order

b. one half-order

c. first-order Correct

d. second order

Explanation

It is easiest to use the first and third run to determine the order.

CHEM126 - CHAPTER 13 - BASIC HOMEWORK / KINETICS I 16

Question 19

What is k? Hint given in feedback

Answer:

Explanation

Substitute the data from one of the runs into the appropriate equation and solve for k. For zero-order, the rate of reaction = k[H₂O₂]⁰ = k. For first-order, the rate of reaction = k[H₂O₂]¹ For one half-order, the rate of reaction = k[H₂O₂]^0.5 For second-order, the rate of reaction = k[H₂O₂]²

CHEM126 - CHAPTER 13 - BASIC HOMEWORK / KINETICS I 17

Question 20

What are the units of k?

Select one:

a. M/s

b. M^0.5/s

c. 1/s or s^-1 Correct

d. 1/(Ms) or M^-1s^-1

e. unitless

Explanation

Khan Academy – How to find units of rate constant k

Question 21

What is the rate when [H₂O₂] = 0.082 M? Hint given in feedback

Answer:

Explanation

Use the rate equation for the correct order with the k that you determined.

CHEM126 - CHAPTER 13 - BASIC HOMEWORK / KINETICS I 18

Question 22

For the reaction 2A(g) + 3B(g) → C(g) + 2D(g) the following experimental data was obtained for the rate:

Run	[A] (M)	[B] (M)	Rate (M/min)
1	0.01	0.2	2.2
2	0.01	0.4	4.4
3	0.02	0.4	8.8

The rate of reaction = kA^xB^y. What is x? Hint given in feedback

Answer:

Explanation

Hint: Notice that in run #2 and #3 the concentration of B does not change. So, it does not change the rate. Therefore, you can use these runs to find the order of the reaction with respect to A. In what two runs is the concentration of A the same? Use these runs to find the order of the reaction with respect to B. From run 2 to 3, [A] doubles. Rate also doubles. This means that x=1.

Question 23

What is y?

Answer:

Explanation

From run 1 to 2, [B] doubles. Rate also doubles. This means that y=1.

Question 24

What is k?

Answer:

Explanation

Plug in values for a single run, as well as the x and y values determined above to solve for k.

Question 25

What are the units of k?

Select one:

a. M/min

b. M^0.5/min

c. 1/min or min^-1

d. 1/(Mmin) or M^-1min^-1 Correct

e. unitless

Explanation

Khan Academy – How to find units of rate constant k

Question 26

What is the rate when [A] = 0.043 M and [B] = 0.038 M? Hint given in feedback

Answer: