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

Question

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

Quizplus · 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.

Which of the Presented Mechanisms Would Be the Most Energetically