Chapter 6
1. Which reaction is fast and has Keq=1?
A) A
Ans: B
B) B
C) C
2. Which reaction has a positive ∆G, assuming that entropy changes are negligible
compared to enthalpy changes?
A) A
Ans: A
B) B
C) C
3. Which reaction is slowest?
A) A
Ans: A
B) B
C) C
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4. In which reaction is Keq > 1?
A) A
Ans: C
B) B
C) C
5. How many transition states are present in the reaction in the energy diagram?
A) 0
B) 1
Ans: C
C) 2
D) 3
E) 4
6. Which of the following letters represents ∆H for the forward reaction in the following
energy diagram?
A) A
Ans: D
B) B
C) C
D) D
E) E
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7. How many transition states and intermediates would the reaction profile have for the
reaction shown below?
A)
3 transition states and 3
intermediates
B) 2 transition states and 2
intermediates
C) 3 transition states and 2
intermediates
Ans: C
D)
E)
2 transition states and 3
intermediates
2 transition states and 1 intermediate
8. Which step would most likely have the largest energy of activation?
A)
B)
C)
D)
Ans:
Step one
Step two
Step three
It cannot be determined from the information provided.
A
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9. Based on the table of relative bond dissociation energies given below, would you predict
the overall reaction to be endothermic or exothermic?
Bond
(CH3)2CH–Cl
H–OH
(CH3)2CH–OH
H–Cl
∆H° (kcal/mol)
80
119
96
103
Cl
+
H2O
step 2
B
A) Exothermic
Ans: A
Cl
OH
Cl
step 1
A
O H2
+
HCl
step 3
C
D
B) Endothermic
10. The equilibrium constant for the conversion of A to D is predicted to be which of the
following?
Cl
+
H2O
step 2
B
A) 1
B) <1
provided.
Ans: C
Cl
+
HCl
step 3
C
C) >1
OH
Cl
step 1
A
OH2
D
D) It cannot be determined from the information
11. The ∆G (free energy change) for the conversion of A to B is predicted to be which of
the following?
Cl
+
step 1
A
A) 0
B) <0
provided.
Ans: C
H2O
O H2
step 2
B
C) >0
Cl
OH
Cl
+
step 3
C
D
D) It cannot be determined from the information
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HCl
12. What kind of reaction does the conversion of A to D represent?
Cl
OH
Cl
+
Cl
step 1
A
O H2
H 2O
+
step 2
step 3
B
C
A) Addition reaction
B) Substitution reaction
Ans: B
HCl
C)
D)
D
Elimination reaction
Subtraction reaction
13. If the conversion of A to B is slow and B to C is fast, what is the rate equation for this
reaction?
Cl
OH
Cl
+
Cl
step 1
A
O H2
H 2O
+
step 2
step 3
B
C
A) rate = k[CH3)2CHCl][H2O]
B) rate = k[CH3)2CHCl]
Ans: B
HCl
C)
D)
D
rate = k[CH3)2CH]+[ H2O]
rate = k[CH3)2CH]+
14. Which compound would you predict to be highest in energy?
Cl
+
H2O
step 1
A
A) A
Ans: B
step 2
B
B) B
O H2
C) C
Cl
OH
Cl
step 3
C
D) D
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D
+
HCl
15. Calculate the Ea for the conversion of C→B.
A) + 3 kcal
Ans: C
B) + 7 kcal
C) + 9 kcal
16. The following is an energy diagram for the conversion of A→B →C. The energies of
activation and ∆H's for each step are also given. Calculate ∆H overall (for A→B→C).
A) + 3 kcal
Ans: A
B) + 7 kcal
C) + 9 kcal
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17. A possible reaction of CH3CH3 with a chlorine radical is:
Bond dissociation energies are:
Calculate ∆H for this reaction.
A) +5 kcal
B) +4 kcal
C) –7 kcal
Ans: B
18. Which of the following energy diagrams corresponds to a one-step exothermic reaction
with a high energy of activation?
A) A
Ans: B
B) B
C) C
D) D
E) E
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19. Which of the following statements is (are) true about the energy diagram below?
b and c label transition states.
The reaction is endothermic.
The reaction mechanism is one step.
(b and c label transition states) and (The reaction is endothermic) are true
statements.
E) Statements (b and c label transition states), (The reaction is endothermic), and
(The reaction mechanism is one step) are all true.
Ans: B
A)
B)
C)
D)
20. Which of the following statements is (are) true about the energy diagram drawn below?
A)
B)
C)
D)
E)
The reaction mechanism has two steps.
b labels a transition state.
The overall reaction is endothermic.
The conversion of a to b is faster than the conversion of b to c.
Both (The reaction mechanism has two steps) and (b labels a transition state) are
true.
Ans: A
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21. Which of the circled C–H bonds has the highest bond dissociation energy?
A) A
Ans: A
B) B
C) C
D) D
E) E
22. Which of the indicated C–H bonds has the lowest bond dissociation energy?
A) A
Ans: A
B) B
C) C
D) D
E) E
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23. Which of the circled C–H bonds has the lowest bond dissociation energy?
A) A
Ans: D
B) B
C) C
D) D
E) E
24. Which of the circled C–H bonds is the weakest?
A) A
Ans: A
B) B
C) C
D) D
E) E
Page 10
25. Which of the following molecules is the correct representation for the transition state for
the following reaction?
O
O
H
+
Br
O H Br
A
A) A
Ans: C
B) B
Br
H
O H
O H
Br
Br
B
C
C) C
26. Which of the following reactions can be classified as a substitution reaction? (Ignore the
reagents used; just compare the structures of the starting material and products.)
A) A
Ans: D
B) B
C) C
D) D
E) E
27. Given the following value, tell whether the starting material or product is favored at
equilibrium.
Keq = 6
A) Starting material favored
Ans: B
B) Product favored
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28. Given the following value, tell whether the starting material or product is favored at
equilibrium.
∆G = 5 kcal/mol
A) Starting material favored
Ans: A
B) Product favored
29. Given the following value, tell whether the starting material or product is favored at
equilibrium.
∆H = 6.5 kcal/mol
A) Starting material favored
Ans: A
B) Product favored
30. Given the following value, tell whether the starting material or product is favored at
equilibrium.
Keq = 0.2
A) Starting material favored
Ans: A
B) Product favored
31. A process that involves symmetrical bond breaking and bond making is a(n):
A) addition reaction.
D) substitution reaction.
B) radical reaction.
E) heterolytic bond breakage.
C) polar reaction.
Ans: B
32. A reaction species that lies at an energy minimum between steps on a reaction energy
diagram is:
A) a transition state.
D) an equilibrium product.
B) the activation energy.
E) a rearranged species.
C) a reaction intermediate.
Ans: C
33. A decrease in which of the following results in an increase in the rate of a chemical
reaction?
A) Energy of activation
D) Collision frequency
B) Temperature
E) Reaction time
C) Concentration
Ans: A
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34. Bond polarity of functional groups is very important for chemical reactivity because:
A) the electron-rich sites in functional groups on one molecule will react with the
electron-poor sites in functional groups on another molecule.
B) like charges in molecules attract each other and lead to a reaction intermediate.
C) unlike charges in molecules repel each other and lead to a reaction intermediate.
D) bond polarity of functional groups in a molecule is not important for chemical
reactivity. Only solvents need to be polar to produce reaction intermediates.
Ans: A
35. A carbocation is all of the following, except:
A) an electrophile.
C)
B) a nucleophile.
D)
Ans: B
a reactive intermediate.
a positively charged species.
36. The value of the equilibrium constant tells:
A) the overall activation energy of the reaction.
B) the rate of the reaction.
C) whether the reaction is endothermic or exothermic.
D) which side of the reaction arrow is energetically favored.
Ans: D
Challenge Questions
37. Which of the following statements about enzymes is true?
A) Enzymes increase the activation energy for a reaction.
B) Enzymes decrease the Keq.
C) Enzymes shift the equilibrium to favor the products.
D) Enzymes cause a reaction to be exothermic.
E) Enzymes lower the transition state for the rate determining step.
Ans: E
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38. Answer the following questions about the reaction coordinate diagram given below.
A)
B)
C)
D)
E)
Ans:
i) 2, ii) C → E, iii) reactants, iv) positive
i) 3, ii) A → C, iii) reactants, iv) positive
i) 5, ii) B → D, iii) products, iv) negative
i) 3, ii) B → D, iii) products, iv) positive
i) 2, ii) E → G, iii) reactants, iv) negative
B
39. For a reaction with ∆H° = -12 kcal mol-1 and ∆S° = 0.01 kcal mol-1, (i) calculate ∆G°
and the equilibrium constant at 30°C, (ii) Is this reaction endothermic or exothermic?
(iii) How does Keq change as T increases?
A) i) ∆G° = 15 kcal/mol, Keq = 1.50 x 10-11, ii) endothermic, iii) Keq increases as T
increases
B) i) ∆G° = -12.3 kcal/mol, Keq = 4.38, ii) exothermic, iii) Keq increases as T
increases
C) i) ∆G° = 12.3 kcal/mol, Keq = 3.50 x 10-8, ii) endothermic, iii) Keq decreases as T
increases
D) i) ∆G° = -15 kcal/mol, Keq = 6.66 x 1010, ii) exothermic, iii) Keq decreases as T
increases
Ans: D
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40. Answer the following questions about the reaction coordinate diagram given below.
A)
B)
C)
D)
E)
Ans:
i) 2, ii) E → G, iii) endergonic, iv) A → C
i) 3, ii) D → F, iii) exergonic, iv) B → D
i) 2, ii) A → C, iii) endergonic, iv) C → E
i) 3, ii) B → D, iii) exergonic, iv) D → F
i) 2, ii) C → E, iii) endergonic, iv) A → C
C
41. The reaction below is one of the steps required in the synthesis of
perhydrohistrionicotoxin, a molecule with interesting biological activity. Classify this
type of reaction.
A) Addition reaction
B) Substitution reaction
Ans: A
C)
D)
Page 15
Elimination reaction
Acid-base reaction