Chem 110 Exam 2 Spring 2008 (Form 1)

CHEM 110 EXAM 2 SPRING 2008 (FORM 1)

Part 1. Multiple Choice (3 pts. each) Circle the ONE BEST answer or fill in the blank where appropriate.

1.Which balanced reaction below has the following rate relationship?

(a) N2O5 → 2 NO2 + ½ O2

2.Given the following balanced equation, what is the rate of appearance of O2 if the rate of disappearance

of O3 is –4.63 x 10−1M/ s?

2 O3 (g) → 3 O2 (g)

(b)0.694 M/ s

3.Which of the following statements is false?

(d)The half-life of a first order reaction is dependent on the initial concentration of reactant.

4.Given the following rate law, how does the rate of reaction change if the concentration of Y is doubled?

Rate = k [X]2[Y]3

(c) The rate of reaction will increase by a factor of 8.

5.How many half-lives are required for a sample of uranium to decay to 12.5 % of its original value?

6.Which of the following is true?

(e)All of the above statements are false.

7.If the activation energy for a given compound is found to be 42 kJ/ mol, with a frequency factor of

8.0 x 1010 s−1, what is the rate constant for this reaction at 298 K?

(e)3.5 x 103 s−1

8.What should be plotted to show that experimental concentration data fits a first-order reaction?

(c) ln [reactant] vs. time

9.Which of the following statements are true?

(a)Dynamic equilibrium occurs when the rate of the forward reaction equals the rate of the reverse reaction.

10. The equilibrium constant is given for two of the reactions below. Determine the value of the missing

equilibrium constant.

A (g) + 2 B (g) AB2 (g)Kc = 59

AB2 (g) + B (g) AB3 (g)Kc = ?

A (g) + 3 B (g) AB3 (g)Kc = 478

11.The reaction below has a Kc value of 61. What is the Kp for this reaction at 500. K?

N2 (g) + 3 H2 (g) 2 NH3 (g)

(d)3.6 x 10−2

12.Express the equilibrium constant for the following reaction:

KClO3 (s) KClO (s) + O2 (g)

(d)K = [O2]

13.Consider the following reaction at equilibrium. What effect will increasing the volume of the reaction

mixture have on the system?

CuS (s) + O2 (g) Cu (s) + SO2 (g)

(b)No effect will be observed.

Part 2. Matching (6 pts.) Match the following (each letter is used only once):

D QK(a)reaction is at equilibrium

C K < < 1(b)reaction does not strongly favor reactant or products

A Q = K(c) reaction will favor formation of reactants

B K ≈ 1(d) reaction favors formation of more products

E Q > > 1(e) reaction has a larger amount of products than reactants

F k(f) rate constant

Part 3. Free response. Answer each question below as completely as possible. Be sure to show all math steps. No work, no credit.

16.(15 pts.) (a)Terpenes are a class of organic compounds that are found in many coniferous trees. These compounds are studied by environmental chemists because they are known to react with ozone.

Use the following data to determine the rate law, then calculate kand report the correct units.

Experiment / [terpene] (M) / [O3] (M) / Initial rate
(M/ s)
1 / 0.10 / 0.050 / 1.25 x 10−3
2 / 0.030 / 0.050 / 1.125 x 10−4
3 / 0.040 / 0.035 / 6.9 x 10−5

[terpene]2 [O3]3

Rate = 6.9E-5 = k[0.040]2[0.035]3 k = 1005 M-4s-1

Rate = k[terpene]2[O3]3 k = 1005 units (of k): M-4s-1 _

(b) Consider the following second order process:

2 AB3 2 AB2 + B2

Assuming the initial reaction mixture contained only 5.50 moles of AB3 in a 1.0 L vessel, what is the concentration of B2 after 1.75 mins.? k = 1.50 M-1min-1.

2.57 M

17. (10 pts.) (a) The decomposition of N2O5 was a workhorse in the early days of reaction kinetics. At 55 °C, the following data were obtained from pressure measurements.

2 N2O5 → 4 NO2 + O2

Time (min) / [N2O5] (mmol/ L)
0 / 14.7
5 / 9.3
10 / 5.9
15 / 3.7
20 / 2.4

(a) Fill in all three boxes below. Only one correlation coefficient is required in each (R or R2).

(b) What is the order of the reaction (must be supported above): first order _

(d) What is the half-life of the reaction above?

t1/2 = ln2/k = ln2/0.090928 = 7.62 min

7.62 min

18. (15 pts.)Consider the following mechanism:

(a) What is the overall reaction?

I2(g) + H2(g) -> 2HI(g)

(b) Identify the intermediate(s) in the mechanism.

Consider the temperature dependence of the rate constant for the decomposition of HI:

2 HI (g) → H2 (g) + I2 (g)

T (K) / k(M−1 s−1)
629 / 3.0
647 / 8.2
666 / 22.3
683 / 52
700 / 116.6
716 / 240.6

(d) Determine the activation energy and the frequency factor (A).

Ea = 189 kJ/mol; A = 1.40E16 M−1 s−1

19. (15 pts.) (a)Hydrogen can be produced via the oxidation of methane with water according to the following reaction:

CH4 (g) + 2 H2O (g) CO2 (g) + 4 H2 (g)

What is the equilibrium concentration of hydrogen in a reaction mixture that initially contains the following partial pressures (Kp = 1.05):

CH4 (atm) / H2O (atm) / CO2 (atm) / H2 (atm)
Initial / 1.00 / 2.00 / 1.00 / 4.00
Change / +x / +2x / -x / -4x
Equilibrium / 1+x / 2+2x / 1-x / 4-4x

Form reactants

4-4(0.450)

p(H2)eq = 2.20 _

Consider the following reaction at equilibrium:

2 KClO3 (s) 2 KCl (s) + 3O2 (g) ΔHrxn < 0

(b) Predict the outcome in each scenario below, circle your choice in each.

(i) O2 is removed from the reaction mixtureshift leftshift rightno effectcan’t tell

(ii) KCl is added to the reaction mixtureshift leftshift rightno effectcan’t tell

(iii) O2 is added to the reaction mixtureshift leftshift rightno effect can’t tell

(iv) N2 is added to the reaction mixtureshift leftshift rightno effectcan’t tell

(v) The reaction mixture is heatedshift leftshift rightno effectcan’t tell