Question 1

Which of the following best describes a nucleophile in organic chemistry?

Accepted Answer

A species with an electron-rich site, often negatively charged or containing a lone pair of electrons.

Question 2

In the addition reaction of HBr to ethylene, which atom acts as the electrophile?

Accepted Answer

The hydrogen atom in HBr

Question 3

Which of the following statements about the equilibrium constant $$K_{eq} is $$TRUE?

Accepted Answer

If $$K_{eq} \gg 1$$, the forward reaction is favored.

Question 4

Which of the following is NOT a type of organic reaction discussed in Chapter 6?

Accepted Answer

Oxidation-reduction reaction

Question 5

A reaction is thermodynamically favorable when:

Accepted Answer

The Gibbs free-energy change $$\Delta G^\circ is $$negative.

Question 6

Which of the following best describes the transition state in a chemical reaction?

Accepted Answer

A structure at maximum energy that cannot be isolated.

Question 7

In a polar reaction mechanism, what does a curved arrow represent?

Accepted Answer

The movement of electron pairs from a nucleophile to an electrophile.

Question 8

Which of the following species is most likely to behave as an electrophile?

Accepted Answer

NO$$_2^+$$

Question 9

Which statement about bond dissociation energy is correct?

Accepted Answer

Heat is released when a bond is formed; heat is absorbed when a bond is broken.

Question 10

Consider the reaction: ethylene + HBr → bromoethane. Which step is associated with the highest activation energy ($$\Delta G$$^{\ddagger}$$) in a two-step mechanism?

Accepted Answer

Formation of the carbocation intermediate

Question 11

Which of the following best explains why $$K_{eq}$$ does NOT provide information about the rate of a reaction?

Accepted Answer

Because $$K_{eq} is $$determined by the energy difference between reactants and products, not by the activation energy.

Question 12

Which formula correctly relates Gibbs free-energy change to enthalpy and entropy?

Accepted Answer

$$\Delta G^\circ = \Delta H^\circ - T\Delta S^\circ$$

Question 13

Which of the following is a plausible reason why biological reactions often proceed faster than laboratory reactions?

Accepted Answer

Biological reactions have many steps, each with a relatively small activation energy.

Question 14

In a two-step exergonic reaction, which energy diagram feature indicates the rate-determining step?

Accepted Answer

The step with the highest activation energy ($$\Delta G$$^{\ddagger}$$)

Question 15

Which of the following statements about reaction intermediates is TRUE?

Accepted Answer

Reaction intermediates are short-lived and may be detected by spectroscopic methods.

Question 16

Which of the following is a correct application of curved arrows in a polar reaction mechanism?

Accepted Answer

A curved arrow starts at a bond and points to an atom to show bond breaking.

Question 17

Which of the following best describes the relationship between bond dissociation energy and reaction rate?

Accepted Answer

Lower bond dissociation energy can make bond breaking easier, potentially increasing reaction rate.

Question 18

Which scenario best illustrates a real-world application of equilibrium and reaction rate concepts?

Accepted Answer

Gasoline and oxygen at room temperature have a favorable equilibrium but react slowly without a spark.

Question 19

Which of the following is TRUE about the energy diagram for a fast, highly exergonic one-step reaction?

Accepted Answer

The activation energy ($$\Delta G$$^{\ddagger}$$) is small and the free-energy change ($$\Delta G^\circ$$) is large and negative.

Chapter 6: Thermodynamics and Mechanisms of Organic Reactions

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