Northrup's Chem 112 Section TTU General Chemistry

----

Chem 112 - Quiz 3A - Spring, 1997
Chapter 16 and 17: Chemical Kinetics and Equilibrium

1. The catalytic converter in an automobile uses NiO and Pt metal to speed the combustion of CO to CO2. This is an example of:

a) homogeneous catalysis
b) heterogeneous catalysis
c) acid hydrolysis
d) enzyme catalysis

2. The decomposition of N2O5(g) --> NO2(g) + NO3(g) proceeds as a first order reaction with a half-life of 30.0 seconds at a certain temperature. If the initial concentration [N2O5]0 = 0.400 M, what is the concentration after 120 seconds?

a) 0.000 M
b) 0.100 M
c) 0.025 M
d) 0.200 M
e) 0.050 M

3. What is the rate constant of the reaction in Problem #2?

a) 2.31 x 10-2 s-1
b) 30.0 s-1>
c) 20.7 s-1>
d) 43.3 s-1>

4. Which equation below best gives the concentration of N2O5 versus time in Problem #2?

5. Radioactive isotope concentrations typically decay by:

a) no simple order
b) zero order kinetics
c) second order kinetics
d) first order kinetics

6. The collision theory of reaction rates:

I. helps to expose how temperature affects the rate.
II. assumes that the rate depends on the frequency at which reactants collide.
III. assumes that reactants must be in correct orientation to react.
IV. assumes that only collisions with energy above the activation energy are successful.

a) I, II, and III are correct. IV is incorrect.
b) I, III, and IV are correct. II is incorrect.
c) II, III, and IV are correct. I is incorrect.
d) All are correct statements.

7. The relationship between the rate constant and temperature is expressed by the:

a) Arrhenius equation
b) rate law
c) integrated rate equation
d) reaction mechanism

8. Identify the INCORRECT statement below:

a) The rate of a typical reaction doubles with a 10° C rise in temperature.
b) The overall rate of reaction is determined by the rate of the fastest elementary step.
c) The reaction mechanism is a step-by-step pathway by which reaction occurs.
d) The reaction mechanism is typically a series of elementary reaction steps.
e) Reaction orders for a single elementary step are equal to the balancing coefficients for that step.

9. Calculator problem - Cyclopropane rearranges to form propene:

CH2CH2CH2 --> CH2=CHCH3

by first-order kinetics. The rate constant is k = 2.74 x 10-3 s-1. The initial concentration of cyclopropane is 0.290 M. What will be the concentration of cyclopropane after 100 seconds?

a) 0.220 M
b) 0.760 M
c) 2.74 x 10-1 M
d) 7.94 x 10-2 M

10. Identify the INCORRECT statement below regarding chemical equilibrium:

a) All chemical reactions are, in principle, reversible.
b) Equilibrium is achieved when the forward reaction rate equals the reverse reaction rate.
c) Equilibrium is achieved when the concentration of species become constant.
d) Equilibrium is achieved when the reaction quotient Q equals the equilibrium constant.
e) Equilibrium is achieved when the reactant and product concentrations become equal.

11. Calculator problem - Nitrogen reacts with hydrogen to form ammonia:

N2(g) + 3 H2(g) <==> 2 NH3(g)

At a certain temperature the equilibrium constant is Kc = 2.0. An equilibrium mixture is found to contain concentrations of N2 equal to 0.15 M and H2 equal to 0.30 M. What is the concentration of NH3 in this mixture?

a) 2.7 x 10-2 M
b) 0.16 M
c) 8.1 x 10-3 M
d) 9.0 x 10-2 M

12. Write the appropriate equilibrium constant expression Kc for the following reaction:

2 CO(g) + O2(g) <==> 2 CO2(g)

13. Suppose we rewrote the balanced reaction in Problem #12 as:

What would be the equilibrium constant for this reaction?

a) same, Kc´ = Kc

b) Kc´ = ˆKc

c) Kc´ = Kc/2

d) Kc´ = Kc2

e) Kc´ = 1/ Kc

14. When Kc >> 1 for a chemical reaction:

a) the equilibrium would be achieved rapidly.
b) the equilibrium would be achieved slowly.
c) reactants would be much more stable than products.
d) product concentrations would be much greater than reactant concentrations at equilibrium.
e) reactant concentrations would be much greater than product concentrations at equilibrium.

15. In the rearrangement reaction:

cyclopropane <==> propene

the equilibrium constant at a certain temperature is Kc = 3.0. A reaction vessel initial having a cyclopropane concentration [cyclopropane]0 = 2.0 M and no propene is allowed to come to equilibrium. What will be the concentration of propene at equilibrium?

a) 0.0 M
b) 0.66 M
c) 1.5 M
d) 2.0 M

For Problems #16 - 20

A proposed mechanism for the decomposition of ozone is:

16. Which step is rate-determining?

a) step (1)
b) step (2)

17. Which species is (are) an unstable intermediate?

a) O2 and O
b) O2
c) O
d) Ar
e) Ar and O

18. Which species is a catalyst?

a) O2
b) O3
c) Ar
d) Ar and O3

19. Which is the best overall rate law consistent with this mechanism?

a) k[O3][O]
b) k[O3]2
c) k[O3]
d) k[O3]2/[O2]

20. The properly written overall balanced equation is:

a) 2 O3 --> 3 O2
b) O3 --> 2 O2
c) 2 O3 + O --> 3 O2 + O
d) 3 O2 --> 2 O3

KEY

1)b 2)c 3)a 4)c 5)d 6)d 7)a 8)b 9)a 10)e 11)d 12)d 13)b 14)d 15)c 16)b 17)c 18)c 19)d 20)a
To send electronic mail to Dr. Northrup ====> snorthrup@tntech.edu, or call 615-372-3421, or come to Foster Hall 333