Deck 6: Understanding Organic Reactions

Question 1

Which of the following statements is true?

A) Bond dissociation energies increase down a column of the periodic table.
B) When $\Delta$ H° is positive, more energy is released in forming bonds than is needed to break bonds.
C) When $\Delta$ H° is negative, more energy is needed to break bonds than is released in forming bonds.
D) Bond dissociation energies decrease down a column of the periodic table.

Answer 1

Bond dissociation energies decrease down a column of the periodic table.

Question 2

Which of the following statements about bond breaking is true?

A) Homolysis and heterolysis require energy.
B) In homolysis, the electrons in the bond are divided unequally.
C) In heterolysis, the electrons in the bond are divided equally.
D) Homolysis generates charged intermediates.

Answer 2

Homolysis and heterolysis require energy.

Question 3

Which of the following statements is not true?

A) Bond breaking is endothermic.
B) The bond dissociation energy for bond breaking is always negative.
C) Bond making is exothermic.
D) The bond dissociation energy for bond formation is always negative.

Answer 3

The bond dissociation energy for bond breaking is always negative.

Question 4

Which of the following statements about the equilibrium constant, K_eq, is true?

A) When K_eq > 1, the equilibrium favors the reactants.
B) When K_eq < 1, the equilibrium favors the products.
C) The size of K_eq tells about the position of equilibrium.
D) For a reaction to be useful, the equilibrium must favor the reactants.

Question 5

Which of the following expressions summarizes the correct relationship between the free energy change, $\Delta$ G°, and the equilibrium constant, K_eq?

A) K_eq > 1 when $\Delta$ G° > 0
B) K_eq > 1 when $\Delta$ G° < 0
C) K_eq < 1 when $\Delta$ G° < 0
D) K_eq < 1 when $\Delta$ G° = 0

Question 6

Using the bond dissociation energies given, calculate $\Delta$ H° for the following reaction. $$\mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 } - \mathrm { Br } + \mathrm { H } _ { 2 } \mathrm { O } \longrightarrow \mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 } - \mathrm { OH } + + \mathrm { HBr }$$

A) +108 KJ/mol
B) -130 KJ/mol
C) -22 KJ/mol
D) +22 KJ/mol

Question 7

What kind of reaction does the conversion of A to B represent?

A) Acid-base reaction.
B) Elimination reaction.
C) Substitution reaction.
D) Addition reaction.

Question 8

Which of the K_eq corresponds to the lowest value of $\Delta$ G°?

A) "K_eq = 10^-3"
B) "K_eq = 10^-2"
C) "K_eq = 10^-1"
D) " $\Delta$ G° cannot be determined"

Question 9

Which of the K_eq corresponds to the most negative value of $\Delta$ G°?

A) K_eq = 1
B) K_eq = 10¹
C) K_eq = 10²
D) K_eq = 10³

Question 10

Which of the following statements is true?

A) Ionic intermediates are formed in radical reactions.
B) Radicals are intermediates in polar reactions.
C) Carbocations are electrophiles.
D) Radicals are nucleophiles.

Question 11

Using the bond dissociation energies given, calculate $\Delta$ H° for the following reaction. $$\left( \mathrm { CH } _ { 3 } \right) _ { 3 } \mathrm { CCl } + \mathrm { H } _ { 2 } \mathrm { O } \longrightarrow \left( \mathrm { CH } _ { 3 } \right) _ { 3 } \mathrm { COH } + \mathrm { HCl } ^ { + }$$

A) +3 KJ/mol
B) -3 KJ/mol
C) -67 KJ/mol
D) +70 KJ/mol

Question 12

Which of the following statements about bond breaking is not true?

A) Homolysis generates uncharged reactive intermediates with unpaired electrons.
B) Homolysis require energy but heterolysis does not require energy.
C) Heterolysis generates charged intermediates.
D) Heterolysis involves unequal sharing of bonding electrons by atoms.

Question 13

Which of the following statements about addition reactions is true?

A) Two $\pi$ bonds are formed.
B) Two $\pi$ bonds are broken.
C) Two $\sigma$ bonds are formed.
D) One $\pi$ bond is formed.

Question 14

Which of the following statements about substitution reactions is true?

A) Substitution reactions involve $\pi$ bonds.
B) Substitution reactions involve $\sigma$ bonds.
C) One $\sigma$ bond breaks and another forms at a different carbon atom.
D) One $\pi$ bond breaks and another forms at the same carbon atom.

Question 15

What kind of reaction does the conversion of A to B represent?

A) Addition reaction.
B) Elimination reaction.
C) Substitution reaction.
D) Oxidation-reduction reaction.

Question 16

Which of the following statements is not true?

A) In polar reactions, a nucleophile reacts with an electrophile.
B) Carbocations are electrophiles.
C) Carbanions are nucleophiles.
D) A half-headed curved arrow shows the movement of an electron pair.

Question 17

Which of the K_eq corresponds to the highest value of $\Delta$ G°?

A) K_eq = 10^-1
B) K_eq = 10^-2
C) K_eq = 10^-3
D) K_eq = 10^-5

Question 18

Which of the following statements about equilibrium is true?

A) Equilibrium favors the products when the energy of the products is higher than the energy of the reactants.
B) Equilibrium favors the reactants when the energy of the product is lower than the energy of the reactants.
C) Equilibrium favors the products when they are less stable than the starting material of a reaction
D) Equilibrium favors the products when they are more stable than the starting material of a reaction.

Question 19

Which of the following statements about elimination reactions is true?

A) Two $\sigma$ bonds are broken.
B) Two $\sigma$ bonds are formed.
C) Two $\pi$ bonds are broken.
D) Two $\pi$ bonds are formed.

Question 20

What kind of reaction does the conversion of A to B represent?

A) Addition reaction.
B) Substitution reaction.
C) Elimination reaction.
D) Acid-base reaction.

Question 21

Which of the following statements about a two-step reaction mechanism is true?

A) The transition states are located at energy minima.
B) Each step is characterized by its own value of $\Delta$ H° and E_a.
C) The rate-determining step has the lower energy transition state.
D) The reactive intermediate is located at an energy maximum.

Question 22

What kind of reaction does the conversion of A to D represent?

A) Addition reaction
B) Substitution reaction
C) Elimination reaction
D) Oxidation-reduction reaction

Question 23

What is the name given to the reaction species that lies at an energy minimum between steps on a reaction energy diagram?

A) Transition state
B) Activation energy
C) Reactive intermediate
D) Equilibrium product

Question 24

The $\Delta$ G° (free energy change) for the conversion of A to B is predicted to be which of the following?

A) " $\Delta$ G° = 0"
B) " $\Delta$ G° < 0"
C) " $\Delta$ G° > 0"
D) "Cannot be determined from the information provided"

Question 25

How many transition states and intermediates would the reaction profile have for the reaction shown below?

A) Three transition states and three intermediates
B) Two transition states and two intermediates
C) Three transition states and two intermediates
D) Two transition states and three intermediates

Question 26

Which of the following statements is true?

A) The product is favored in reaction in which $\Delta$ H° is a positive value.
B) Entropy decreases when an acyclic compound forms a ring.
C) In homolytic bond cleavage, entropy decreases and favors formation of products.
D) The starting material is favored in a reaction in which $\Delta$ H° is a negative value.

Question 27

A decrease in which of the following results in an increase in the rate of a chemical reaction?

A) Energy of activation
B) Concentration
C) Temperature
D) Kinetic energy

Question 28

The equilibrium constant for the conversion of A to D is predicted to be which of the following?

A) K_eq = 1
B) K_eq < 1
C) K_eq > 1
D) Cannot be determined from the information provided

Question 29

Which reaction is slowest?

A) A
B) B
C) C

Question 30

Which of the following statements is true?

A) Fast reactions have small rate constants.
B) Slow reactions have large rate constants.
C) A rate equation contains concentration terms for all reactants involved in a one-step mechanism.
D) A rate equation contains concentration terms for all the reactants involved in a multi-step reaction.

Question 31

How many transition states are present in the reaction in the energy diagram?

A) 0
B) 1
C) 2
D) 3

Question 32

Which reaction has a positive $\Delta$ G°, assuming that entropy changes are negligible compared to enthalpy changes?

A) A
B) B
C) C

Question 33

Which step would most likely have the largest energy of activation?

A) Step one
B) Step two
C) Step three
D) It cannot be determined from the information provided

Question 34

If the conversion of A to B is slow and B to C is fast, what is the rate equation for this reaction?

A) Rate = k[(CH₃)₂CHCl][H₂O]
B) Rate = k[(CH₃)₂CHCl]
C) Rate = k[(CH₃)₂CH]⁺[H₂O]
D) Rate = k[(CH₃)₂CH]⁺

Question 35

Which of the following statements is true?

A) The size of the activation energy tells us about the reaction mechanism.
B) The size of the activation energy tells us about the reaction rate.
C) A slow reaction has low activation energy.
D) A fast reaction has large activation energy.

Question 36

Which of the following letters represents $\Delta$ H° for the forward reaction in the following energy diagram?

A) A
B) B
C) C
D) D

Question 37

In which reaction is K_eq > 1?

A) A
B) B
C) C

Question 38

Which reaction is fast and has K_eq= 1?

A) A
B) B
C) C

Question 39

Which of the following statements is not true?

A) "Two reactions can have identical values for $\Delta$ H° but very different E_a values."
B) "The larger the activation energy, the slower the reaction."
C) " $\Delta$ H° determines the height of the energy barrier."
D) "The lower the activation energy, the faster the reaction."

Question 40

Which of the following reaction quantities will have an effect on reaction rate?

A) " $\Delta$ G°"
B) " $\Delta$ H°"
C) "K_eq"
D) "E_a"

Question 41

Which compound would you predict to be highest in energy?

A) A
B) B
C) C
D) D

Question 42

Which of the following statements about a catalyst is true?

A) A catalyst accelerates a reaction by changing the amount of reactant and product at equilibrium.
B) A catalyst accelerates a reaction by lowering the energy of activation.
C) A catalyst accelerates a reaction by raising the energy of activation.
D) A catalyst accelerates a reaction by lowering the equilibrium constant.

Question 43

Which of the following statements about enzymes is true?

A) Enzymes increase the activation energy for a reaction.
B) Enzymes decrease the equilibrium constant.
C) Enzymes shift the equilibrium to favor the product.
D) Enzymes lower the transition state for the rate-determining step.