Chemistry 2C Practice Midterm 2 - University of California ...

Name _______________________
Chemistry Specialist: Alicia Hart
Professors: Dr. Toupadakis & Dr. Lievens
Fall 2013

Chemistry 2C
Practice Midterm 2

Instructions:

You will have EXACTLY 50 minutes to complete the exam on test day, but this practice
exam is a bit longer. Please take this practice exam under standard conditions (i.e. closed
book). SHOW ALL OF YOUR WORK in the space provided. Lastly, read each question
CAREFULLY and determine what the question is asking BEFORE you put down your
answer. Feel free to reference the periodic table that you are supposed to keep in your
notebook.

Please Note:

We will go over this exam during the Midterm 2 Review on Wed 11/20
from 6:10 – 8:00 pm in 194 Young. It WILL benefit you greatly to come to the test review
prepared and ready to go over the solutions.

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I. Multiple-Choice Questions

1. Complete the reaction:

SiO2 + 2 C

a) SiO + C2O
b) SiC + CO2
c) Si + 2 CO(g)
d) SiCO + CO
e) SiC2O2

2. Choose the INCORRECT statement:

a) Xenon compounds in several different oxidation states have been formed.
b) The noble gas compounds are very stable.
c) Xenon compounds are excellent reducing agents.
d) The Noble gas (except helium) electron configuration has ns2np6.
e) The formation of noble gas compounds were predicted many years before they

were made.

3. What is the rate law for the following reaction and its mechanism?

O3 → O2 + O· (Slow)

O· + O3 → 2O2 (Fast)

2O3 → 3O2 (overall reaction)

a) rate = k[O3]
b) rate = k[O3]2
c) rate = k[O3]2/[O2]
d) rate = k[O3]/[O2]
e) rate = k[O3][O2]

4. Which of these is the strongest oxidizing agent?

a) HClO2
b) HClO3
c) HClO4
d) KClO3
e) KClO2

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5. Through a set of temperature-controlled experiments, researchers determined the rate law
for the following reaction:

C2H5I + -OH C2H5OH + I-

The data from the different trials are listed in the table below.

Trial [C2H5I] [-OH] Initial Rate
1 2.0 x 10-3 6.0 x 10-3 1.3 x 10-4
2 4.0 x 10-3 6.0 x 10-3 5.2 x 10-4
3 4.0 x 10-3 1.2 x 10-2 5.2 x 10-4

What is the rate law expression for this reaction?

a) rate = k[C2H5I][OH]2
b) rate = k[OH]2
c) rate = k[C2H5I]2
d) rate = k[C2H5I]
e) rate = k[C2H5I][OH]

6. Which incorrectly shows the main product of the reaction of the indicated alkali metal
with excess oxygen?

a) Li/Li2O
b) Na/Na2O2
c) K/K2O2
d) Rb/RbO2
e) Cs/CsO2

7. Write the general reaction for a group 1 (1A) metal with water.

a) 2 M(s) + 2 H2O(l) → H2O2(aq) + 2 MH(s)
b) 2 M(s) + 2 H2O(l) → 2 MOH(aq) + H2(g)
c) M(s) + H2O(l) → MO(s) + H2(g)
d) 2 M(s) + H2O(l) → M2O(s) + H2(g)
e) 2 M(s) + 2H2O(l) → M(OH)2(s) + H2(g)

8. For the given reaction, use the following information to determine the rate of
disappearance of A.
2A + B2 C

rate of reaction = 4 x 10-3 Ms-1 = ∆C/∆t

a) -8 x 10-3 Ms-1
b) 8 x 10-3 Ms-1
c) 4 x 10-3 Ms-1
d) -4 x 10-3 Ms-1
e) Not enough information.

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9. What are the units of the rate constant for a second-order reaction in A and fourth order
overall?

a) mol-1 L s-1
b) mol-1 L-1 s-1
c) mol-2 L s-1
d) mol-3 L3 s-1
e) mol-3 L-3 s-1

10. The first order reaction A B has a half-life = 50 secs. What percent of the sample has
been reacted after 150 secs?

a) 12.5%
b) 25%
c) 50%
d) 87.5%
e) 100%

11. Choose the incorrect statement:

a) Reaction rate is always a positive value.
b) The exponents in the rate law are determined experimentally.
c) Rate of disappearance is always a negative value.
d) Transition states cannot be isolated.
e) The units for the rate of a first order reaction M-2s-1

12. What is the half-life for a second-order reaction (A Products) if the [A] = 0.580 M at
t = 300 secs (k= 2.0 x 10-3 M-1s-1) ?

a) 560 secs
b) 332 secs
c) 893 secs
d) 420 secs
e) None of the above.

13. Which of the following exists in more different allotropic forms than any other element?

a) xenon
b) tellurium
c) sulfur
d) phosphorus
e) oxygen

14. Choose the INCORRECT statement about the most common oxidation states:

a) For Ti, it is +4
b) For Sc, it is +2
c) For V, it is +5
d) For Cr, it is +6
e) For Mn, it is +7

4

II. Short Answer Questions

15. Draw the energy (H) profile labeling the reactants, products, change in enthalpy, transition
states, intermediates, and energy of activation for a reaction if you know the following:
a. The reaction is a three-step reaction.
b. Enthalpy of products is lower than enthalpy of the reactants.
c. Activation energies of first and third step are equal and two-thirds the activation
energy of the second step.
d. The first intermediate is higher in Energy than the second.

16. The reaction CH3Cl + NH3 CH3NH2 + HCl is second order in CH3Cl and zero
order in NH3. The value of the rate constant is 0.014 M-1s-1. What is the rate of the reaction
when [CH3Cl] = 0.325 M and [NH3] = 0.560 M?

17. I need to double the rate of a chemical reaction at 25°C by increasing the temperature.
The activation energy for the reaction is found to be 22.2 kJ. What temperature in °C would
I have to change the reaction to?

18. In the first-order reaction, A B, [A] = 0.600 M initially and 0.250 M after 22.0 min, at
what time will [A] = 0.150 M?

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19. For the reaction 2 NO(g) + Cl2(g) 2 NOCl(g) the following data was collected at 25°C.

time (s) Initial [Cl2]

0.00 0.255
1.25 0.213

a) Calculate the average reaction rate in M.min-1.

b) Calculate the rate of disappearance of NO(g) in M.min-1.

c) Calculate the rate of appearance of at 25°C NOCl(g) in atm.min-1.

20. For the reaction N2O3(g) ⇒ NO(g) + NO2(g) at room temperature the following data
was collected (other points not noted were also placed on the line):

-9.31 (Note data is not real for the reaction)
-19.31
ln[N2O3]

20 40
time (seconds)

a) What is the rate law for this reaction?

b) What is the value of the rate constant?

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III. Long Answer Questions

21. Through a set of temperature-controlled experiments, researchers determined the rate
law for the following reaction:

2A(aq) + B(g) + 5C(g) + 3D (aq) 6E(aq)

The data from the different trials are listed in the table below.

Trial [A] [B] [C] [D] Initial Rate
1 0.10 0.10 0.40 0.10 2.10 x 10-5
2 0.137 0.10 0.60 0.20 3.16 x 10-4
3 0.137 0.10 0.80 0.20 3.16 x 10-4
4 0.137 0.0547 0.90 0.20 2.33 x 10-4
5 0.137 0.1 0.40 0.269 7.68 x 10-4

a) What is the rate law expression for this reaction?

b) What is the overall order of the reaction?
c) The value of the rate constant is?

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22. Below is a proposed mechanism for a chemical reaction along with assumed relative
rates. First, determine the overall balanced reaction assuming the proposed mechanism is
correct. Next, determine the rate law that is expected to be observed based on this
mechanism. Show work, clearly label constants and state any assumptions.

B2 ⇔ 2B (fast)

B + A2 ⇔ BA2 (fast)

BA2 + B 2AB (slow)

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