Question 1

Do you expect the initiation step in the free radical chlorination of 2,2-dimethylpropane to have a positive or negative DS? Explain briefly.

Accepted Answer

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Question 2

Energy is ________ when bonds are formed and is ________ when bonds are broken; therefore, bond dissociation energies are always ________.

Accepted Answer

Energy is released (exothermic) when bonds are formed and consumed (endothermic) when bonds are broken. Bond dissociation energies are therefore always positive and endothermic. Choice B correctly identifies these thermodynamic aspects of bond formation/dissociation.

Question 3

If stronger bonds are formed and weaker bonds are broken, then the reaction is ________.

Accepted Answer

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Question 4

Does one expect ΔS° in a propagation step of the free-radical chlorination of methane to be greater than zero, less than zero, or approximately equal to zero? Briefly explain your choice.

Accepted Answer

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Question 5

Which of the following is true for the termination step of a free radical chlorination reaction?

Accepted Answer

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Question 6

Consider the bond dissociation energies listed below in kcal/mol.  
These data show that the carbon-bromine bond is weakest when bromine is bound to a ________.

Accepted Answer

The bond dissociation energies show that the carbon-bromine bond is weakest when bromine is bound to a tertiary carbon. This is because the neighboring carbons in a tertiary carbon skeleton have greater electron density and more inductive effect, making the carbon-bromine bond less strong than in a primary or secondary carbon skeleton.

Question 7

Consider the elementary step in the solvolysis of isopropyl chloride shown below and write the rate equation for this step. (CH₃)₂CHCl → (CH₃)₂CH⁺ + Cl^-

Accepted Answer

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Question 8

What reactive species is produced in the initiation step of the free radical chlorination of 2,2-dimethylpropane?

Accepted Answer

In the initiation step of free radical chlorination, a chlorine molecule is broken down into two chlorine atoms by homolytic cleavage. One of these chlorine atoms then forms a covalent bond with a hydrogen atom on the substrate to produce a reactive species, which in this case is a methyl radical.

Question 9

Predict the sign of DS° in the combustion of propane.

Accepted Answer

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Question 10

Which of the presented mechanisms would be the most energetically favorable and thus the most likely mechanism to actually occur for the following free radical chain reaction? (bond dissociation energies -- H-H = 104 kcal/mol; Cl-Cl = 58 kcal/mol; H-Cl = 103 kcal/mol) H₂ + Cl₂ 2 HCl

Accepted Answer

In the reaction, a chlorine radical (Cl∙) reacts with a hydrogen sulfide molecule (H₂) to form a hydrogen radical (H∙) and hydrogen chloride (HCl), as shown in option B. This is the most energetically favorable mechanism, as it involves the breaking of the weaker bond (Cl-Cl, 58 kcal/mol) and the formation of the stronger bond (H-Cl, 103 kcal/mol) compared to the other options. Additionally, the formation of two H-Cl bonds is also favorable, contributing to the overall negative ∆H of the reaction. Option A and Option C involve the formation of an H-H bond, which has a higher bond dissociation energy than H-Cl, making these mechanisms less energetically favorable. Option D also involves the formation of an H-H bond, and the breaking of two H-Cl bonds, which is energetically unfavorable.

Question 11

Predict the enthalpy (ΔH) value for the theoretical reaction below, and indicate whether it is endothermic or exothermic. The bond dissociation energy for each bond in Kcal/mol is shown below each reactant and product.

Accepted Answer

The enthalpy change (ΔH) is calculated by subtracting the total bond energies of the products from the total bond energies of the reactants: (63 + 88) - (47 + 96) = +8 Kcal/mol, indicating an endothermic reaction.

Question 12

The hydrogenation of acetylene to produce ethane is shown below. Is ΔS° for this reaction positive, negative, or impossible to predict? Explain your reasoning. C₂H₂ (g) + 2H₂ (g) → C₂H₆ (g)

Accepted Answer

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Question 13

Which compound has the smaller bond dissociation energy for its carbon-chlorine bond, CH₃Cl or (CH₃)₃CCl? Explain your reasoning.

Accepted Answer

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Question 14

Of the two C-H bonds shown, which has the smaller bond dissociation energy? Explain your choice. (CH₃)₂CH-H vs. CH₃CH₂-H

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Question 15

Given the bond dissociation energies below (in kcal/mol), calculate the overall ΔH° for the following reaction: (CH₃)₃CH + Br₂ → (CH₃)₃CBr + HBr (CH₃)₃C-H 91 (CH₃)₃C-Br 65 Br-Br 46 H-Br 88 CH₃-Br 70

Accepted Answer

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Question 16

Predict the signs of DH° and DS° in the reaction of cyclohexene with H₂ to form cyclohexane.

Accepted Answer

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Question 17

Given the bond dissociation energies below (in kcal/mol), estimate the ΔH° for the propagation step CH₃CH₂CH₂-H 98 (CH₃)₂CH-H 95 Cl-Cl 58 H-Cl 103 CH₃CH₂CH₂-Cl 81 (CH₃)₂CH-Cl 80

Accepted Answer

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Question 18

Do you expect the initiation step in the free radical chlorination of 2,2-dimethylpropane to be endo- or exothermic? Explain briefly, and comment on the sign of DH.

Accepted Answer

The answer of Do you expect the initiation step in...

Question 19

The bond dissociation energy is the amount of energy required to break a bond ________.

Accepted Answer

Bond dissociation energy is the amount of energy required to break a bond in a way that each of the two atoms ends up with one electron from the bond. This is called homolytic cleavage. Option A correctly describes homolytic bond cleavage.

Question 20

Given the chlorination of acetone shown below, choose the correct rate law. CH₃COCH₃ + Cl₂ → CH₃COCH₂Cl + HCl

Accepted Answer

The rate law for a chemical reaction cannot be determined solely from the stoichiometry of the reaction; it must be determined experimentally because it depends on the mechanism of the reaction, which is not provided by the stoichiometry.

Quiz 4: The Study of Chemical Reactions

Do you expect the initiation step in the free radical chlorination of 2,2-dimethylpropane to have a positive or negative DS? Explain briefly.

Energy is when bonds are formed and is when bonds are broken; therefore, bond dissociation energies are always .

If stronger bonds are formed and weaker bonds are broken, then the reaction is ________.

Does one expect ΔS° in a propagation step of the free-radical chlorination of methane to be greater than zero, less than zero, or approximately equal to zero? Briefly explain your choice.

Which of the following is true for the termination step of a free radical chlorination reaction?

Consider the bond dissociation energies listed below in kcal/mol. These data show that the carbon-bromine bond is weakest when bromine is bound to a ________.

Consider the elementary step in the solvolysis of isopropyl chloride shown below and write the rate equation for this step. (CH₃)₂CHCl → (CH₃)₂CH⁺ + Cl^-

What reactive species is produced in the initiation step of the free radical chlorination of 2,2-dimethylpropane?

Predict the sign of DS° in the combustion of propane.

Which of the presented mechanisms would be the most energetically favorable and thus the most likely mechanism to actually occur for the following free radical chain reaction? (bond dissociation energies -- H-H = 104 kcal/mol; Cl-Cl = 58 kcal/mol; H-Cl = 103 kcal/mol) H₂ + Cl₂ 2 HCl

Predict the enthalpy (ΔH) value for the theoretical reaction below, and indicate whether it is endothermic or exothermic. The bond dissociation energy for each bond in Kcal/mol is shown below each reactant and product.

The hydrogenation of acetylene to produce ethane is shown below. Is ΔS° for this reaction positive, negative, or impossible to predict? Explain your reasoning. C₂H₂ (g) + 2H₂ (g) → C₂H₆ (g)

Which compound has the smaller bond dissociation energy for its carbon-chlorine bond, CH₃Cl or (CH₃)₃CCl? Explain your reasoning.

Of the two C-H bonds shown, which has the smaller bond dissociation energy? Explain your choice. (CH₃)₂CH-H vs. CH₃CH₂-H

Given the bond dissociation energies below (in kcal/mol), calculate the overall ΔH° for the following reaction: (CH₃)₃CH + Br₂ → (CH₃)₃CBr + HBr (CH₃)₃C-H 91 (CH₃)₃C-Br 65 Br-Br 46 H-Br 88 CH₃-Br 70

Predict the signs of DH° and DS° in the reaction of cyclohexene with H₂ to form cyclohexane.

Given the bond dissociation energies below (in kcal/mol) , estimate the ΔH° for the propagation step CH₃CH₂CH₂-H 98 (CH₃) ₂CH-H 95 Cl-Cl 58 H-Cl 103 CH₃CH₂CH₂-Cl 81 (CH₃) ₂CH-Cl 80

Do you expect the initiation step in the free radical chlorination of 2,2-dimethylpropane to be endo- or exothermic? Explain briefly, and comment on the sign of DH.

The bond dissociation energy is the amount of energy required to break a bond ________.

Given the chlorination of acetone shown below, choose the correct rate law. CH₃COCH₃ + Cl₂ → CH₃COCH₂Cl + HCl

Quiz 4: The Study of Chemical Reactions

Do you expect the initiation step in the free radical chlorination of 2,2-dimethylpropane to have a positive or negative DS? Explain briefly.

Energy is ________ when bonds are formed and is ________ when bonds are broken; therefore, bond dissociation energies are always ________.

If stronger bonds are formed and weaker bonds are broken, then the reaction is ________.

Does one expect ΔS° in a propagation step of the free-radical chlorination of methane to be greater than zero, less than zero, or approximately equal to zero? Briefly explain your choice.

Which of the following is true for the termination step of a free radical chlorination reaction?

Consider the bond dissociation energies listed below in kcal/mol. These data show that the carbon-bromine bond is weakest when bromine is bound to a ________.

Consider the elementary step in the solvolysis of isopropyl chloride shown below and write the rate equation for this step. (CH3)2CHCl → (CH3)2CH+ + Cl-

What reactive species is produced in the initiation step of the free radical chlorination of 2,2-dimethylpropane?

Predict the sign of DS° in the combustion of propane.

Which of the presented mechanisms would be the most energetically favorable and thus the most likely mechanism to actually occur for the following free radical chain reaction? (bond dissociation energies -- H-H = 104 kcal/mol; Cl-Cl = 58 kcal/mol; H-Cl = 103 kcal/mol) H2 + Cl2 2 HCl

Predict the enthalpy (ΔH) value for the theoretical reaction below, and indicate whether it is endothermic or exothermic. The bond dissociation energy for each bond in Kcal/mol is shown below each reactant and product.

The hydrogenation of acetylene to produce ethane is shown below. Is ΔS° for this reaction positive, negative, or impossible to predict? Explain your reasoning. C2H2 (g) + 2H2 (g) → C2H6 (g)

Which compound has the smaller bond dissociation energy for its carbon-chlorine bond, CH3Cl or (CH3)3CCl? Explain your reasoning.

Of the two C-H bonds shown, which has the smaller bond dissociation energy? Explain your choice. (CH3)2CH-H vs. CH3CH2-H

Given the bond dissociation energies below (in kcal/mol), calculate the overall ΔH° for the following reaction: (CH3)3CH + Br2 → (CH3)3CBr + HBr (CH3)3C-H 91 (CH3)3C-Br 65 Br-Br 46 H-Br 88 CH3-Br 70

Predict the signs of DH° and DS° in the reaction of cyclohexene with H2 to form cyclohexane.

Given the bond dissociation energies below (in kcal/mol) , estimate the ΔH° for the propagation step CH3CH2CH2-H 98 (CH3) 2CH-H 95 Cl-Cl 58 H-Cl 103 CH3CH2CH2-Cl 81 (CH3) 2CH-Cl 80

Do you expect the initiation step in the free radical chlorination of 2,2-dimethylpropane to be endo- or exothermic? Explain briefly, and comment on the sign of DH.

The bond dissociation energy is the amount of energy required to break a bond ________.

Given the chlorination of acetone shown below, choose the correct rate law. CH3COCH3 + Cl2 → CH3COCH2Cl + HCl

Energy is when bonds are formed and is when bonds are broken; therefore, bond dissociation energies are always .

Consider the elementary step in the solvolysis of isopropyl chloride shown below and write the rate equation for this step. (CH₃)₂CHCl → (CH₃)₂CH⁺ + Cl^-

Which of the presented mechanisms would be the most energetically favorable and thus the most likely mechanism to actually occur for the following free radical chain reaction? (bond dissociation energies -- H-H = 104 kcal/mol; Cl-Cl = 58 kcal/mol; H-Cl = 103 kcal/mol) H₂ + Cl₂ 2 HCl

The hydrogenation of acetylene to produce ethane is shown below. Is ΔS° for this reaction positive, negative, or impossible to predict? Explain your reasoning. C₂H₂ (g) + 2H₂ (g) → C₂H₆ (g)

Which compound has the smaller bond dissociation energy for its carbon-chlorine bond, CH₃Cl or (CH₃)₃CCl? Explain your reasoning.

Of the two C-H bonds shown, which has the smaller bond dissociation energy? Explain your choice. (CH₃)₂CH-H vs. CH₃CH₂-H

Given the bond dissociation energies below (in kcal/mol), calculate the overall ΔH° for the following reaction: (CH₃)₃CH + Br₂ → (CH₃)₃CBr + HBr (CH₃)₃C-H 91 (CH₃)₃C-Br 65 Br-Br 46 H-Br 88 CH₃-Br 70

Predict the signs of DH° and DS° in the reaction of cyclohexene with H₂ to form cyclohexane.

Given the bond dissociation energies below (in kcal/mol) , estimate the ΔH° for the propagation step CH₃CH₂CH₂-H 98 (CH₃) ₂CH-H 95 Cl-Cl 58 H-Cl 103 CH₃CH₂CH₂-Cl 81 (CH₃) ₂CH-Cl 80

Given the chlorination of acetone shown below, choose the correct rate law. CH₃COCH₃ + Cl₂ → CH₃COCH₂Cl + HCl