Chemistry 3202 Unit 1 Test 1 2005-06

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CDLI - Chemistry 3202 Unit 1 Test 1 Reaction Kinetics and Equilibrium December 2006 Part I - Multiple Choice: Using the form on page 4, circle the letter of the best response. 1.

Which states that particles of matter are in constant random motion? A. collision theory B. Hess’s law C. kinetic molecular theory D. law of chemical equilibrium

2.

Reactants A and B collided with the correct orientation required to form product C; however, product C did not form. What best explains this observation? A. the activated complex was stable B. the collision lacked sufficient intensity C. the kinetic energy of the colliding particles was too high D. no catalyst was present

3.

In the diagram on the right, which label represents the activation energy of the reverse reaction? A. Q B. R C. S D. T

4.

In the diagram on the right, which label represents the heat of reaction? A. Q B. R C. S D. T

Q T EP

R

S

Progress of Reaction

5.

The activation energy for this reaction, Cu + S → CuS + 53.1kJ , is 50 kJ. What is the activation energy of the reverse reaction? (hint: draw a diagram) A. 3.1 kJ B. 50 kJ C. 53.1 kJ D. 103.1 kJ

6.

Substance X is a highly unstable, undetectable, short lived structure formed upon the collision of reactants. How should substance X be classified? A. activated complex B. catalyst C. elementary particle D. reaction intermediate

Chemistry 3202 Unit 1 Test 1 2005-06

7.

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Which reaction should proceed at a faster rate if surface area of a reactant and pressure are increased? A. Zn(NO3 )2(aq) + Na2S (aq) → ZnS (s) + 2 NaNO3 (aq) B.

ZnS(l)

→

C.

Zn (s)

+

Cl2

D.

Zn(s)

+

H2SO4(aq)

Zn(s) (g)

+

S (l)

→

ZnCl2

(s)

H2(g)

→

ZnSO4

+

(aq)

8.

What effect does a catalyst have on a chemical reaction? A. it changes the reaction mechanism B. it decreases the heat of reaction C. it increases the intensity of collisions D. it blockes the activated complex

9.

Consider this proposed reaction mechanism: Step 1 :

H2

Step 2 :

N (g)

NO (g)

+

(g)

+

NO (g)

H2O (g)

→ →

N2

(g)

N (g)

+ +

O (g)

Step 3 : H2 (g) + O (g) → H2O (g) ______________________________________________ 2 H2

+

(g)

2 NO (g)

→

2 H2O (g)

What is the role of O(g) in this reaction mechanism? A. activated complex B. catalyst C. product D. reaction intermediate 10. Which is the rate determining step? 1

3 2 4

EP

Progress of Reaction A. B. C. D.

step 1 step 2 step 3 step 4

+

N2

(g)

Chemistry 3202 Unit 1 Test 1 2005-06

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11. Which change will result in a faster rate for the overall reaction in this proposed mechanism? Step 1 :

Cl2

Step 2 :

CH4

(g) (g)

→ +

2 Cl(g) Cl (g)

fast CH3 (g)

→

+

HCl (g)

slow

Step 3 : CH3 (g) + Cl (g) → CH3Cl (g) fast ______________________________________________ Cl2

A. B. C. D.

(aq)

+

CH4

(g)

→

CH3Cl (g)

+

HCl (g)

increase the concentration of CH3(g) increase the concentration of CH4(g) reduce the pressure on the system reduce the temperature of the system

12. What is the catalyst for the formation of ground level ozone? A. carbon monoxide B. methyl tert-butyl ether C. nitrogen monoxide D. tetraethyl lead 13. What is equal in an equilibrium? A. activation energy of forward and reverse reactions B. final concentrations of reactants and products C. opposing rates of change D. starting concentrations of reactants

Use this equation A ⇌ B and the graph to the right to answer the next two items. Labels T1 to T4 represent four times when concentrations of species A and B were sampled. 14. When is the forward reaction proceeding at the fastest rate? A. T1 B. T2 C. T3 D. T4 15. When is equilibrium achieved? A. T1 B. T2 C. T3 D. T4

T1 T2 T3 T4

Concentration

A B

Progress of reaction

Chemistry 3202 Unit 1 Test 1 Page 4 of 6 Name: ____________________________________ School: _______________________page:___of___

Chemistry 3202 Unit 1 Test 1 Answer Sheet Part 1: For each item, circle the letter corresponding to your choice. 1.

A

B

C

D

6

A

B

C

D

11. A

B

C

D

2.

A

B

C

D

7.

A

B

C

D

12. A

B

C

D

3.

A

B

C

D

8.

A

B

C

D

13. A

B

C

D

4.

A

B

C

D

9.

A

B

C

D

14. A

B

C

D

5.

A

B

C

D

10. A

B

C

D

15. A

B

C

D

Part II: Constructed Responses: Complete each item in the space provided. State final answers in sentence form and follow the rules for rounding/significant digits. 16. Magnesium metal reacts with ethanoic acid. Mg (s)

a)

+

CH3COOH (aq)

→

H2

(g)

+

Mg ( CH3COO )2

(aq)

(2)

Predict the effect of each change on the overall rate of reaction, and explain your prediction in terms of the collision theory. i) diluting the ethanoic acid with water

(2)

ii) increasing the temperature of the ethanoic acid from 20°C to 30°C.

(2)

b) Describe an experiment you could carry out to verify the prediction you made in item ii above.

Chemistry 3202 Unit 1 Test 1 Page 5 of 6 Name: ____________________________________ School: _______________________page:___of___

(3) 17. a) Sketch a potential energy diagram for this uncatalysed reaction 2 O3

+

300 kJ

→

3 O2

assuming an activation energy for the forward reaction of 500 kJ. Label the reactants, products, activated complex, activation energy of forward reaction, and heat of reaction. (Leave room for item c below.)

Ep

Progress of Reaction b)

Consider this proposed mechanism for the catalyzed reaction: Step 1 :

O3

+

OH

→

O2

+

HO2

fast

Step 2 : HO2 + O3 → OH + 2 O2 slow ____________________________________________

(1)

i)

Identify the reaction intermediate and briefly explain your choice.

(1)

ii)

Identify the catalyst and briefly explain your choice.

(1)

c) On the diagram you produced above, indicate the reaction pathway for the catalyzed reaction using a dotted line.

Chemistry 3202 Unit 1 Test 1 Page 6 of 6 Name: ____________________________________ School: _______________________page:___of___

(2)

(1)

18. a)

The modern catalytic converter is a ceramic structure coated with metals like platinum, rhodium and palladium. The structure consists of numerous honeycomb shaped channels. In terms of rates of reaction, what is the purpose of the honeycomb design? Explain.

b) Give two reasons why tetraethyl lead is no longer added to gasoline.

19. Equal amounts of hydrogen and iodine gases are added to an empty round bottomed flask. The gases react to produce hydrogen iodide and eventually this equilibrium is established. H2

+

I2

⇌

2 HI

(1.5)

a) Describe the changes in the concentrations of the reactants and products as this equilibrium is established. (a diagram may be helpful here)

(1.5)

b) List the conditions that must be met in order for the equilibrium to be maintained.