CHM 2046C Module Nine
Kotz 5^th Edition Chapter 15
Sample Multiple Choice #2 Answers
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1. The correct answer is:
heat of reaction.

Explanation:
The rate of the reaction is independent of whether the reaction is endothermic or exothermic as long as its temperature does not change while the reaction is taking place.

Solution Reference:
Page 692, Reaction Conditions and Rate

2. The correct answer is:


Explanation:
The rate of the reaction is the change in concentration divided by the change in time (Dc/Dt or dc/dt) divided by the appropriate stoichiometric coefficient and converted to a positive number.

Solution Reference:
Page 688, Rates of Chemical Reactions

3. The correct answer is:


Explanation:
Substitute the appropriate units into the rate law and solve for k.


Solution Reference:
Page 697, Determination of the Rate Equation

4. The correct answer is:
Cannot tell from the information given above.

Explanation:
The rate law must be determined experimentally. It cannot be obtained from a consideration of the stoichiometric equation.

Solution Reference:
Page 697, Determination of the Rate Equation

5. The correct answer is:
1.

Explanation:


Solution Reference:
Page 696, The Order of a Reaction

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6. The correct answer is:
it is endothermic.

Explanation:
The change in enthalpy for a reaction does not tell us anything about the rate of a chemical reaction. The sign of DH tells us whether the reaction is endothermic or exothermic.

Solution Reference:
Page 687, Chemical Kinetics

7. The correct answer is:
is approximately doubled for a 10°C rise in temperature.

Explanation:
Let us look at each of the responses: a. The rate of a reaction decreases with time because the concentration of the reactants is decreasing. b. is dependent of the amount of contact surface of a solid involved. c. the rate depends upon the magnitude of the activation energy. d. For many chemical reactions with 10°C rise in temperature, the number of molecules with enough energy to react approximately doubles. e. The rate varies proportionately with the absolute temperature.

Solution Reference:
Page 710, A Microscopic View of Reaction Rates.

8. The correct answer is:
1 and 4

Explanation:
Thermodynamics is concerned with the energy changes in a reaction. Kinetics is concerned with the reaction mechanism, the rate of reaction, and the temperature dependence of the reaction.

Solution Reference:
Page 687, Chemical Kinetics and Page 710, A Microscopic View of Reaction Rates

9. The correct answer is:
the reaction rate decreases, but k remains the same.

Explanation:
This is a difficult question for most students since OH^- does not appear directly in the rate law. This prompts many students to select option e. The sodium hydroxide decreases the H⁺ concentration.

Solution Reference:
Page 697, Reaction Conditions and Rate

10. The correct answer is:
31.2 min.

Explanation:


Solution Reference:
Page 707, Half-Life and First-Order Reactions

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11. The correct answer is:
1.0 x 10^-3.

Explanation:


Solution Reference:
Page 707, Half-Life and First-Order Reactions

12. The correct answer is:
3.

Explanation:
Rate = k[Cl₂][NO]²

Solution Reference:
Page 697, Determination of the Rate Equation

Question Instructions: The reaction between selenious acid and iodide ion in acid solution is

H₂Se₂O₃ + 6 I^- + 4H⁺ --> Se(s) + 2I₃^- + 3H₂O

The data below were measured at 0°C.

13. The correct answer is:
4.

Explanation:
Compare Experiments I and II. Doubling the concentration of H₂S₂O₃ results in the rate doubling. Therefore, in the rate law H₂S₂O₃ is first order.

Solution Reference:
Page 697, Determination of the Rate Equation

Question Instructions: The reaction between selenious acid and iodide ion in acid solution is

H₂Se₂O₃ + 6 I^- + 4H⁺ --> Se(s) + 2I₃^- + 3H₂O

The data below were measured at 0°C.

14. The correct answer is:
4.

Explanation:
Compare Experiments III and IV. Doubling the concentration of H⁺ results in the rate quadrupling. Therefore, the reaction is second order in H⁺. (2/1)² = 4/1.

Solution Reference:
Page 697, Determination of the Rate Equation

Question Instructions: The reaction between selenious acid and iodide ion in acid solution is

H₂Se₂O₃ + 6 I^- + 4H⁺ --> Se(s) + 2I₃^- + 3H₂O

The data below were measured at 0°C.

15. The correct answer is:
27.

Explanation:
Compare Experiments IV and V. Doubling the concentration of I- results in the rate increasing by a factor of 8. Therefore, I^- appears in the reaction to the third power. (3/1)³ = 27/1

Solution Reference:
Page 697, Determination of the Rate Equation

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Question Instructions: The reaction between selenious acid and iodide ion in acid solution is

H₂Se₂O₃ + 6 I^- + 4H⁺ --> Se(s) + 2I₃^- + 3H₂O

The data below were measured at 0°C.

16. The correct answer is:
k[H₂Se₂O₃][H⁺]²[I^-]³.

Solution Reference:
Page 697, Determination of the Rate Equation

17. The correct answer is:
R = k [(CH₃)₃CCl]

Explanation:
The rate of reaction is directly proportional to the concentration of (CH₃)₃CCl and the rate is independent of the concentration of OH^-. Therefore [OH^-] is to the zero power.

Solution Reference:
Page 697, Determination of the Rate Equation

18. The correct answer is:
ln A - ln A_o = -kt

Solution Reference:
Page 700, First-Order Reactions

19. The correct answer is:
5000

Explanation:


Solution Reference:
Page 703, Second-Order Reactions

20. The correct answer is:
providing an alternative reaction pathway.

Explanation:
By decreasing the activation energy and providing another pathway.

Solution Reference:
Page 718, Effect of Catalysts on Reaction Rate

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21. The correct answer is:
62 kJ.

Explanation:
Draw a potential energy diagram for this reaction or use the relationship.
DH_reaction = E_af - E_ar
38 kJ = 100 kJ - E_ar
E_ar = 100 - 38 = 62 kJ

Solution Reference:
Page 718, Effect of Catalysts on Reaction Rate

22. The correct answer is:
1.4 x 10⁷ s^-1.

Explanation:

23. Question Instructions: The complete mechanism for a reaction is considered to occur in two steps, one of which is slow and the other fast:

A + B --> C + D (slow)
A + C --> E + F (fast)
The correct answer is:
k[A][B].

Explanation:
In each elementary reaction, the stoichiometric coefficients are the respective exponents in the rate law for that step.

Solution Reference:
Page 724, Reaction Mechanisms

24. Question Instructions: The complete mechanism for a reaction is considered to occur in two steps, one of which is slow and the other fast:

A + B --> C + D (slow)
A + C --> E + F (fast)
The correct answer is:
2A + B --> D + E + F.

Explanation:
The stoichiometric equation is given by the sum of the elementary reactions.

Solution Reference:
Page 724, Reaction Mechanisms

25. The correct answer is:
Rate = k₂K_eq [CHCl₃][Cl₂]^1/2.

Explanation:
1.
Solving for [Cl] we get [Cl] = K_eq^1/2 [Cl₂]^1/2

2. Rate = k₂ [CHCl₃][Cl]
Combining equations 1 and 2 by eliminating the active intermediate [Cl] and getting the rate law in terms of the reactants we get
Rate = k₂ K_eq^1/2 [CHCl₃][Cl₂]^1/2

Solution Reference:
Page 724, Reaction Mechanisms

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