Question 1

Which of the following best describes the initiation step in the free-radical chlorination of methane?

Accepted Answer

A chlorine molecule splits homolytically into two chlorine atoms upon absorption of a photon.

Question 2

What is the correct expression for the equilibrium constant $$K_{eq}$$ for the reaction $$aA + bB \rightleftharpoons cC + dD$$?

Accepted Answer

$$K_{eq} = \dfrac{[C]^c [D]^d}{[A]^a [B]^b}$$

Question 3

Which statement about free radicals is TRUE?

Accepted Answer

Halogens have seven valence electrons, so one will be unpaired in the radical.

Question 4

In the propagation step of methane chlorination, what is the role of the chlorine atom?

Accepted Answer

It abstracts a hydrogen atom from methane, forming HCl and a methyl radical.

Question 5

Which of the following is a termination step in the free-radical chain reaction?

Accepted Answer

Two free radicals combine to form a nonradical compound.

Question 6

Given the reaction $$CH_4$$ + $$Cl_2$$ ightarrow CH_3Cl + HCl$$, and K$$_{eq} = 1.1 	imes $$10^{19}$$, what does the large value of $$K_{eq}$$ indicate?

Accepted Answer

The reaction strongly favors the products at equilibrium.

Question 7

Which equation correctly relates the standard free energy change $$\Delta G^\circ to $$the equilibrium constant $$K_{eq}$$?

Accepted Answer

$$\Delta G^\circ = -RT \ln K_{eq}$$

Question 8

Which factor(s) determine the value of $$\Delta G^\circ$$ for a chemical reaction?

Accepted Answer

Both enthalpy $$\Delta H^\circ$$ and entropy $$\Delta S^\circ.$$

Question 9

Which of the following best describes an exothermic reaction?

Accepted Answer

Heat is released and $$\Delta H^\circ is $$negative.

Question 10

Which statement about entropy $$\Delta S^\circ is $$correct?

Accepted Answer

Spontaneous reactions maximize disorder and minimize enthalpy.

Question 11

What is the bond dissociation enthalpy (BDE) used for in chemical reactions?

Accepted Answer

To estimate $$\Delta H$$ for a reaction by considering the energy required to break bonds.

Question 12

In homolytic cleavage, what happens to the electrons in the bond?

Accepted Answer

Each atom gets one electron from the bond.

Question 13

Which of the following is TRUE about the enthalpy change in the chlorination of methane?

Accepted Answer

The reaction is exothermic because the energy released in forming bonds exceeds the energy required to break bonds.

Question 14

Which of the following is a correct description of the propagation steps in the free-radical chlorination of methane?

Accepted Answer

Both of the above steps occur in sequence to propagate the chain reaction.

Question 15

If the value of $$\Delta G^\circ$$ for a reaction is negative, what does this imply about the reaction?

Accepted Answer

The reaction is spontaneous and favors product formation.

Question 16

Which of the following is NOT a possible termination step in a free-radical chain reaction?

Accepted Answer

A methyl radical collides with a chlorine atom to form methyl chloride.

Question 17

Which of the following best explains why reactions favor products with the lowest enthalpy?

Accepted Answer

Products with lower enthalpy have stronger bonds and are more stable.

Question 18

Which of the following is TRUE regarding the effect of increasing temperature on the equilibrium constant $$K_{eq}$$ for an exothermic reaction?

Accepted Answer

Increasing temperature decreases $$K_{eq}$$ for an exothermic reaction.

Question 19

Which of the following is a correct statement about the entropy change $$\Delta S^\circ in a $$chemical reaction?

Accepted Answer

$$\Delta S^\circ is $$the change in randomness, disorder, or freedom of movement.

Study Notes: Chemical Reactions and Thermodynamics in Organic Chemistry

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