Chemistry 2
Practice Exam 5 1.   Which statement(s) are TRUE ?

I.   Rate is the change in quantity per change in time.
II.   Rate is directly proportional to the concentration at a given time.
III.  Instantaneous rate is the rate at the moment the reactants are mixed.

a)   I & II
b)   I & III
c)   II & III
d)   I, II, & III
e)   II only

2.   Which equation describes the relationship between the rates at which O2 is consumed and NO is produced?

4 NH3(g) + 5 O2(g) 4 NO(g) + 6 H2O(g)

a)   - (O2)/ t = (NO)/ t
b)   - 4 (O2)/ t = 5 (NO)/ t
c)   - 5 (O2)/ t = 4 (NO)/ t
d)   - (1/5) (O2)/ t = (1/4) (NO)/ t
e)   - (1/4) (O2)/ t = (1/5) (NO)/ t

3.   The rate is 2nd order in NO and 1st order in O2 with a rate constant of 1.73 x 103 M-2 sec-1 for a given reaction. What is the rate if the initial concentrations are NO = 0.0130 M and O2 = 0.0220 M ?

a)   4.95 x 10-7 M/sec
b)   2.15 x 10-3 M/sec
c)   6.43 x 10-3 M/sec
d)   1.09 x 10-2 M/sec
e)   4.95 x 10-1 M/sec

4.   What is the reaction rate law for the possible mechanism described below for the reaction of NO and O2.

2 NO(g) + O2(g) 2 NO2(g)

Step 1: 2 NO N2 + O2 (fast)
Step 2: N2 + 2 O2 2 NO2 (slow)

a) Rate = k (NO)2
b) Rate = k (N2) (O2)2
c) Rate = k (NO)2 (O2)
d) Rate = k (NO)2 (O2)3
e) Rate = k (NO2 (N2) (O2)2

5.   Use the data below to determine the rate law for the reaction.

4 A + 3 B 2 C

 Trial # Init. Conc. of A (M) Init. Conc. of B (M) Instant. Rate (M/sec) 1 0.100 0.100 5.00 2 0.300 0.100 45.0 3 0.100 0.200 10.0 4 0.300 0.200 90.0

a)   Rate = k (A)2 (B)1
b)   Rate = k (A)3 (B)1
c)   Rate = k (A)4 (B)3
d)   Rate = k (A)1 (B)2
e)   Rate = k (A)2.63 (B)0

6.   The following reaction obeys the rate law below. What is the reaction order for the individual reactants and for the overall order ?

H2O2(aq) + 3 I-(aq) + 2 H+(aq) I3-(aq) + 2 H2O(l)

Rate = k (H2O2) (I-)

 Order of H2O2 Order of I- Order of H+ Overall Order a) 1 3 2 6 b) 1 1 0 2 c) 2 2 1 5 d) 1 3 0 4 e) 2 1 1 4

7.   What are the units of the rate constant for the following reaction ?

2 Br-(aq) + H2O2 + 2 H+(aq) Br2(aq) + 2 H2O(l)

Rate = k(Br-) (H2O2) (H+)

a)   M/sec
b)   M2/sec
c)   M3/sec
d)   M-2 sec-1
e)   M-3 sec-1

8.   The decomposition of H2O2 is first order in H2O2. How long will it take for the 0.50 M sample to decompose to 0.10 M if the rate constant is 5.6 x 10-2 sec-1 ?

H2O2(aq) 2 H2O(l) + O2(g)

a)   0.0902 sec
b)   7.10 sec
c)   12.5 sec
d)   16.4 sec
e)  28.7 sec

9.   Iodine-123 is a radioactive isotope with a first order half-life of 13.1 hours. It is used to study thyroid gland functions. What is the rate constant for the process?

a)   0.0382 hr-1
b)   0.0529 hr-1
c)   0.153 hr-1
d)   9.08 hr-1
e)   18.9 hr-1

10.   Plutonium-239 (first order half-life = 2.41 x 104 yr) is a serious nuclear waste disposal problem. If a sample must decay to 0.78 % of the original amount to reach a tolerable level of radioactivity, how long must the 239Pu be stored ?

a)   2.72 x 102 years
b)   8.63 x 103 years
c)   7.32 x 104 years
d)   1.69 x 105 years
e)   2.88 x 105 years

11.  What is the rate of O3 appearance if the rate of disappearance of O2 is 2.17 x 10-5 M/sec ?

3 O2(g) 2 O3(g)

a)   7.23 x 10-6 M/sec
b)   1.09 x 10-5 M/sec
c)   1.45 x 10-5 M/sec
d)   3.26 x 10-5 M/sec
e)   4.34 x 10-5 M/sec

12.   In a potential Energy diagram which has the forward Ea = 200 kJ/mol and
the H° = -50 kJ/mol. What is the reverse Ea ?

a)   150 kJ/mol
b)   200 kJ/mol
c)   250 kJ/mol
d)   300 kJ/mol

13.   In the first order decomposition of CS2, the following data was collected. What is the value of the rate constant ?

Rate = k (CS2)1

 Trial # Init. Conc. of CS2 (M) Instant. Rate (M/sec) 1 0.044 1.2 x 10-7 2 0.055 1.5 x 10-7

a)   1.0 x 10-5 sec-1
b)   3.7 x 10-5 sec-1
c)   5.0 x 10-5 sec-1
d)   2.7 x 10-6 sec-1
e)   1.3 x 10-7 sec-1

14.  In the atmosphere, chlorofluorocarbons, CFC's, absorb photons to produce ·Cl atoms. Chlorine atoms react with ozone, O3, by the following mechanism. Which statement concerning the mechanism is TRUE ?

Step 1: O3 + ·Cl ·ClO + O2
Step 2: ·ClO + O ·Cl + O2

overall rxn: O3 + O 2 O2

a)   ·Cl and ·ClO are both catalysts.
b)   ·Cl and ·ClO are both intermediates
c)   ·Cl is a catalyst and ·ClO is an intermediate.
d)   ·Cl is an intermediate and ·ClO is a catalyst.
e)   Information about the slow step must be given.

15.   A biochemist studied the hydrolysis of sucrose (table sugar) and plotted the data in the graphs below. What information can be inferred from these graphs ?

C12H22O11(s) + H2O(l) C6H12O6(aq) + C6H12O6(aq)

1st plot: ln(C12H22O11) vs time is a straight line.
2nd plot: 1/ (C12H22O11) vs time is a curve.
3rd plot: (C12H22O11) vs time is a curve.

a)   The reaction is 1st order in sucrose.
b)   The reaction is 2nd order in sucrose.
c)   The reaction is 3rd order in sucrose.
d)   The reaction is pseudo first order in water.
e)   No information can be inferred from the graphs.

16.   Which statement is TRUE ?

a)   The equilibrium constant increases upon addition of a catalyst.
b)   A catalyst speeds up both the forward and reverse reaction rates.
c)   The higher the activation energy, the faster the rate of the reaction.
d)   A catalyst increases the rate by decreasing the number of collisions.
e)   At a given temperature, all molecules have the same kinetic energy.

17.   The following reaction diagram depicts the atmospheric reaction of O atoms. The arrow marked 2) corresponds to

O + H2O 2 OH

a)   D H° rxn
b)   reverse Ea
c)   forward Ea
d)   the transition state
e)   catalyzed forward Ea

18.   BONUS: Sodium-24, with a first order half life of 15 hours, is used to study blood circulation. If a patient is injected with a 24NaCl solution, how much radioactivity remains after four days, if the initial radioactivity is 2.5 x 105 dps?

a)   1.19 dps
b)   9.18 dps
c)   2.29 x 106 dps
d)   3.0 x 107 dps
e)   2.10 x 107 dps