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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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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 |

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