Q: Given the following bond enthalpies: $$\text{Cl-Cl} = 242\ \text{kJ/mol}$$, $$\text{C-H} = 435\ \text{kJ/mol}$$, $$\text{C-Cl} = 350\ \text{kJ/mol}$$, $$\text{H-Cl} = 432\ \text{kJ/mol}$$, what is the enthalpy change ($$\Delta H) $$for the reaction $$CH_4$$ + $$Cl_2$$ \rightarrow CH_3Cl + HCl$$?

$$\Delta H = -103\ \text{kJ/mol}$$

Question 1

Which of the following best describes the role of curved arrows in organic reaction mechanisms?

Accepted Answer

They show the movement of electrons during bond formation and breaking.

Question 2

In the free-radical halogenation of methane, which step is responsible for the creation of the first reactive intermediate?

Accepted Answer

Initiation

Question 3

Which equation correctly expresses the equilibrium constant $$K_{eq}$$ for the reaction $$A + B \rightleftharpoons C + D$$?

Accepted Answer

$$K_{eq} = \frac{[C][D]}{[A][B]}$$

Question 4

During the propagation step of methane chlorination, which species abstracts a hydrogen atom from methane?

Accepted Answer

Cl$$\cdot$$

Question 5

Which of the following statements about bond-dissociation enthalpy (BDE) is correct?

Accepted Answer

BDE is the energy required to break a bond homolytically in a gaseous molecule.

Question 6

Given the following bond enthalpies: $$	ext{Cl-Cl} = 242\ 	ext{kJ/mol}$$, $$	ext{C-H} = 435\ 	ext{kJ/mol}$$, $$	ext{C-Cl} = 350\ 	ext{kJ/mol}$$, $$	ext{H-Cl} = 432\ 	ext{kJ/mol}$$, what is the enthalpy change ($$\Delta H) $$for the reaction $$CH_4$$ + $$Cl_2$$ ightarrow CH_3Cl + HCl$$?

Accepted Answer

$$\Delta H = -103\ 	ext{kJ/mol}$$

Question 7

Which factor increases the rate of a chemical reaction according to the Arrhenius equation $$k = Ae$$^{-E_a/RT}$$?

Accepted Answer

Increasing the temperature $$T$$

Question 8

In the context of free-radical halogenation, why does fluorine react explosively compared to chlorine and bromine?

Accepted Answer

Fluorine has a lower bond-dissociation energy, making it highly reactive.

Question 9

Which of the following best explains why the chlorination of methane is exothermic?

Accepted Answer

The bonds formed are stronger than the bonds broken.

Question 10

Which step in the free-radical chain reaction mechanism is responsible for stopping the chain reaction?

Accepted Answer

Termination

Question 11

What is the effect of increasing the concentration of reactants on the rate of a reaction, according to the rate equation $$	ext{rate} = k[A]^m[B]^n$$?

Accepted Answer

The rate increases.

Question 12

Which of the following is true about the transition state in a chemical reaction?

Accepted Answer

It has the highest energy along the reaction pathway.

Question 13

In the halogenation of propane, which type of hydrogen is most likely to be abstracted by a halogen radical?

Accepted Answer

Secondary hydrogen

Question 14

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

Accepted Answer

Lower activation energy leads to a faster reaction rate.

Question 15

Which of the following is the correct expression for Gibbs free energy change ($$\Delta G) in $$terms of enthalpy ($$\Delta H) $$and entropy ($$\Delta S$$)?

Accepted Answer

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

Question 16

During the termination step of methane chlorination, which of the following is a possible product?

Accepted Answer

CH$$_3CH$_3$$

Question 17

Which statement about reaction intermediates is correct?

Accepted Answer

They are generally less stable and do not accumulate.

Question 18

Which of the following best explains why bromine reacts more selectively than chlorine in alkane halogenation?

Accepted Answer

Bromine has a higher activation energy, favoring abstraction from more stable hydrogens.

Question 19

Which of the following is true regarding the effect of temperature on the number of molecules with sufficient energy to react?

Accepted Answer

Increasing temperature increases the number of molecules with required energy.

Question 20

In a multistep reaction, which step is typically rate-determining?

Accepted Answer

The step with the highest activation energy.

Study of Chemical Reactions: Mechanisms, Thermodynamics, and Kinetics (Organic Chemistry)

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