Practice Quiz Chapter 16

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1.

Reaction intermediates differ from activated complexes in that

A.

they are stable molecules with normal bonds and are frequently isolated.

B.

they are molecules with normal bonds rather than partial bonds and can occasionally be isolated.

C.

they are intermediate structures which have characteristics of both reactants and products.

D.

they are unstable and can never be isolated.

E.

all reactions involve reaction intermediates, but not all have activated complexes.



2.

According to the collision theory of reaction rates, what are the three requirements which must be met before an elementary reaction between two molecules can occur?


Answer:


3.

Consider the following mechanism for the oxidation of bromide ions by hydrogen peroxide in aqueous acid solution.
H+   +   H2O2   ↔     H2O+–OH (rapid equilibrium)
H2O+–OH   +   Br-   → HOBr   +   H2O (slow)
HOBr   +   H+   +   Br-   →    Br2   +   H2O (fast)
Which of the following rate laws is consistent with the mechanism?

A.

Rate = k[H2O2][H+]2[Br-]

B.

Rate = k [H2O+–OH][Br-]

C.

Rate = k[H2O2][H+][Br-]

D.

Rate = k[HOBr][H+][Br-][H2O2]

E.

Rate = k[Br-]



4.

Tetrafluoroethylene, C2F4, can be converted to octafluorocyclobutane which can be used as a refrigerant or an aerosol propellant. A plot of 1/[C2F4] vs. time gives a straight line with a slope of 0.0448 L mol-1s-1. What is the rate law for this reaction?

A.

Rate = 0.0448 (L mol-1s-1)[C2F4]

B.

Rate = 22.3 (mol L-1s)[C2F4]

C.

Rate = 0.0448 (L mol-1s-1)[C2F4]2

D.

Rate = 22.3 (mol L-1s)[C2F4]2

E.

Rate = 0.0448 s-1 [C2F4]



5.

Consider the following reaction
8A(g)   +   5B(g)   →   8C(g)   +   6D(g)
If [C] is increasing at the rate of 4.0 mol L-1s-1, at what rate is [B] changing?

A.

-0.40 mol L-1s-1

B.

-2.5 mol L-1s-1

C.

-4.0 mol L-1s-1

D.

-6.4 mol L-1s-1

E.

none of the above, since its rate of change must be positive



6.

In the gas phase at 500.°C, cyclopropane reacts to form propene in a first-order reaction. The figure shows the natural logarithm of the concentration of cyclopropane (in mol/L) plotted versus time.
a.   Explain how this plot confirms that the reaction is first order.
b.   Calculate the first-order rate constant, k.
c.   Determine the initial concentration of cyclopropane in this experiment.


Answer:


7.

The decomposition of dinitrogen pentaoxide has an activation energy of 102 kJ/mol and ΔH°rxn = + 55 kJ/mol. What is the activation energy for the reverse reaction?

A.

27 kJ/mol

B.

47 kJ/mol

C.

55 kJ/mol

D.

102 kJ/mol

E.

More information is needed, since this is a Hess's law calculation.



8.

Briefly list the features/properties common to all catalysts and how they work. Draw a labeled reaction energy diagram as part of your answer.


Answer:


9.

In the collision theory of reaction rates, the rate constant for a bimolecular reaction can be written as
k = z⋅p⋅exp(-Ea/RT)
In one sentence each, clearly explain the physical meaning (interpretation) of the following three factors which appear in the above expression:
a.   z
b.   p
c.   exp(-Ea/RT)


Answer:


10.

A reactant R is being consumed in a first-order reaction. What fraction of the initial R is consumed in 4.0 half-lives?

A.

0.94

B.

0.87

C.

0.75

D.

0.13

E.

0.063



11.

Which of the following sets of units could be appropriate for a zero-order rate constant?

A.

s-1

B.

L mol-1 s-1

C.

L2 mol-2 s-1

D.

L3 mol-3 s-1

E.

mol L-1 s-1



12.

The rate law for the reaction 3A → C is
Rate = 4.36 × 10-2 L mol-1 hr-1[A]2
What is the half-life for the reaction if the initial concentration of A is 0.250 M?

A.

0.0109 hr

B.

0.0629 hr

C.

15.9 hr

D.

23.9 hr

E.

91.7 hr



13.

Cyclobutane decomposes to ethene in a first-order reaction. From measurements of the rate constant (k) at various absolute temperatures (T), the accompanying Arrhenius plot was obtained (ln k versus 1/T).
a. Calculate the energy of activation, Ea.
b. Determine the value of the rate    constant at 740. K. (In the plot, the units of k are s-1.)


Answer:


14.

Ammonium cyanate (NH4CNO) reacts to form urea (NH2CONH2). At 65°C the rate constant, k, is 3.60 L mol-1s-1. What is the rate law for this reaction?

A.

Rate = 3.60 L mol-1s-1 [NH4CNO]

B.

Rate = 3.60 L mol-1s-1 [NH4CNO]2

C.

Rate = 0.28 mol L-1s [NH4CNO]

D.

Rate = 0.28 mol L-1s [NH4CNO]2

E.

Rate = 3.60 L mol-1s-1 [NH2CONH2]-1



15.

2NOBr(g)   →   2NO(g)   +   Br2(g)

[NOBr](mol L-1)

Rate (mol L-1s-1)

0.0450

1.62 × 10-3

0.0310

7.69 × 10-4

0.0095

7.22 × 10-5

Based on the initial rate data above, what is the value of the rate constant?

A.

0.0360 L mol-1s-1

B.

0.800 L mol-1s-1

C.

1.25 L mol-1s-1

D.

27.8 L mol-1s-1

E.

0.0360 s-1



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