1. Which of the Following Statements Is Always True?Answer

Question 1

1.  Which of the following statements is always true?Answer

Exothermic reactions have lower activation energies than endothermic reactions.
The rate for a reaction depends on the concentrations of all the reactants.
The rate of a catalyzed reaction is independent of the concentration of the catalyst.
The rate constant is independent of the concentrations of the reacting species.
The rate law can be determined from the stoichiometric equation.

5 points

Question 2

1.  For the formation of 1 mol of nitrosyl chloride at a given temperature, ΔH = -40 kJ.
NO(g) + ½Cl2(g) → NOCl(g)
The activation energy for this reaction is 84 kJ/mol. What is the activation energy for the reverse reaction?Answer

-40 kJ/mol
44 kJ/mol
84 kJ/mol
124 kJ/mol
-124 kJ/mol

5 points

Question 3

1.  The rate constant for a reaction at 40.0°C is exactly 2 times that at 20.0°C. Calculate the Arrhenius energy of activation for the reaction.Answer

2.00 kJ/mol
5.8 kJ/mol
26.4 kJ/mol
3.18 kJ/mol
none of these

5 points

Question 4

1.  The following mechanism has been suggested for the reaction between nitrogen monoxide and oxygen:
NO(g) + NO(g) ↔ N2O2(g) (fast)
N2O2(g) + O2(g) → 2NO2(g) (slow)
According to this mechanism, the experimental rate law isAnswer

second-order in NO and zero-order in O2.
second-order in NO and first-order in O2.
first-order in NO and first-order in O2.
first-order in NO and second-order in O2.
first-order in NO and zero-order in O2.

5 points

Question 5

1.  Which of the following corresponds to the correct integrated expression for a first-order reaction?Answer

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5 points

Question 6

1.  For a certain second-order decomposition reaction, the rate is 0.48 mol/(L · s) when the concentration of the reactant is 0.33 mol/L. What is the rate constant for this reaction?Answer

1.45 L/(mol · s)
0.48 L/(mol · s)
0.23 L/(mol · s)
0.69 L/(mol · s)
4.4 L/(mol · s)

5 points

Question 7

1.  The oxidation of ammonia produces nitrogen and water via the following reaction:
4NH3(g) + 3O2(g) → 2N2(g) + 6H2O(l)
Suppose the rate of formation of H2O(l) is 3.0 mol/(L · s). Which of the following statements is true?Answer

The rate of formation of N2 is 2.0 mol/(L · s).
The rate of consumption of NH3 is 2.0 mol/(L · s).
The rate of consumption of O2 is 2.0 mol/(L · s).
The rate of consumption of NH3 is 0.50 mol/(L · s).
The rate of formation of N2 is 1.3 mol/(L · s).

5 points

Question 8

1.  Below is a proposed mechanism for the decomposition of H2O2.
H2O2 + I- → H2O + IO- slow
H2O2 + IO- → H2O + O2 + I- fast
Which of the following statements is incorrect?Answer

The reaction is first-order with respect to [I-].
The reaction is first-order with respect to [H2O2].
I- is a catalyst.
The net reaction is 2H2O2 → 2H2O + O2.
IO- is a catalyst.

5 points

Question 9

1.  The rate constant for a first-order reaction is 1.6 × 10-2 s-1 at 738 K and 3.5 × 10-2 s-1 at 918 K. What is the activation energy?Answer

11 kJ/mol
24 kJ/mol
2900 kJ/mol
24 kJ/mol
11 kJ/mol

5 points

Question 10

1.  The nuclide 96Nb decays by a first-order process with a rate constant of 2.96 × 10-2 h-1. How long will it take for 69.0% of the initial amount of 96Nb to be consumed?Answer

39.6 h
23.3 h
33.8 h
12.5 h
10.5 h

5 points

Question 11

1.  For a given reaction, the rate constant, k, was determined at different temperatures. To obtain the activation energy, one should plotAnswer

k vs. T.
log k vs. T.
ln k vs. T.
k vs. 1/T.
ln k vs. 1/T.

5 points

Question 12

1.  In aqueous solution, iodine reacts with acetone as represented by the following equation:
I2(aq) + CH3COCH3(aq) → CH3COCH2I(aq) + H+(aq) + I-(aq)
The experimental rate law is Rate = k[H+][CH3COCH3]. According to the information above, an increase in the hydrogen ion concentration has what effect on the reaction?Answer

It increases the value of the equilibrium constant.
It decreases the value of the equilibrium constant.
It increases the rate of the reaction.
It decreases the rate of the reaction.
It does not affect the rate of the reaction.

5 points

Question 13

1.  A reaction that is second-order in one reactant has a rate constant of 2.0 × 10-2 L/(mol · s). If the initial concentration of the reactant is 0.240 mol/L, how long will it take for the concentration to become 0.120 mol/L?Answer

35 s
104 s
210 s
2100 s
350 s

5 points

Question 14

1.  A mechanism that explains the rate law, Rate = k[(CH3)3CO2C(CH3)3], for the gas-phase thermal decomposition of di-tert-butyl peroxide is given below.

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2. 
For this reaction, the rate-determining step(s) must beAnswer

step 1.
step 2.
step 3.
2 times step 2.
step 1 + step 2 + step 3.

5 points

Question 15

1.  Consider the reaction
aA + bB

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2.  dD + eE C = catalyst
The rate law is
Rate = k[A]qr[C]s
Which of the following statements is incorrect?Answer

The exponents q, r, and s are often integers.
The exponents q and r are always equal to the coefficients a and b, respectively.
The exponent s must be determined experimentally.
The symbol k represents the rate constant.
The overall reaction order is q + r + s.

5 points

Question 16

1.  For the hypothetical first-order reaction A → products, k = 0.0472 s-1. If the initial concentration of A is 0.671 M, how long would it take for A to be 81.8% consumed?Answer

36.1 s
21.2 s
14.7 s
4.26 s
31.6 s

5 points

Question 17

1.  A second-order reaction starts with an initial concentration of 0.100 mol/L of the reactant. If the rate constant is 2.2 × 10-2 L/(mol · s), what is the time required to decrease the initial concentration to 0.050 mol/L?Answer

450 s
31.5 s
2.27 s
1400 s
680 s

5 points

Question 18

1.  For the elementary reaction A + B → C + D, what is the predicted rate law?Answer

Rate = k[A]
Rate = k[A]2
Rate = k2
Rate = k
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Rate = k[A]/[C]

5 points

Question 19

1.  The complete mechanism for a reaction is considered to occur in two steps, one of which is slow and the other fast:
A + 2B → C + D slow
A + C → E + F fast
What is the rate law predicted by this mechanism?Answer

Rate = k[A]2
Rate = k[A][C]
Rate = k[A]2[C]
Rate = k[A][C]
Rate = k[A]2

5 points

Question 20

1.  The reaction between selenous acid and the iodide ion in acid solution is
H2SeO3(aq) + 6I-(aq) + 4H+(aq) → Se(s) + 2I3-(aq) + 3H2O(l)
The data in the following table were measured at 0°C.

Experiment / [H2SeO3]0 (M) / [H+]0 (M) / [I-]0 (M) / Initial Rate [mol/(L · s)]
1 / 1.00 × 10-4 / 2.00 × 10-2 / 3.00 × 10-2 / 5.30 × 10-7
2 / 2.00 × 10-4 / 2.00 × 10-2 / 3.00 × 10-2 / 1.06 × 10-6
3 / 3.00 × 10-4 / 4.00 × 10-2 / 3.00 × 10-2 / 6.36 × 10-6
4 / 3.00 × 10-4 / 8.00 × 10-2 / 3.00 × 10-2 / 2.54 × 10-5
5 / 3.00 × 10-4 / 8.00 × 10-2 / 6.00 × 10-2 / 2.04 × 10-4
6 / 2.00 × 10-4 / 2.00 × 10-2 / 6.00 × 10-2 / 8.48 × 10-6

2.  Tripling the initial concentration of I- while holding the initial concentrations of H2SeO3 and H+ constant increases the initial rate of the reaction by a factor ofAnswer

3.
6.
8.
9.
27.

5 points

Question 21

1.  For the first-order reaction
½N2O4(g) → NO2(g); ΔH = 28.6 kJ
the activation energy is 53.7 kJ/mol. What is the activation energy for the reverse reaction?Answer

25.1 kJ/mol
15.2 kJ/mol
53.7 kJ/mol
82.3 kJ/mol
-53.7 kJ/mol