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Chapter 3: Problem 58

Suggest a reason for the fact that ultraviolet light causes \(\mathrm{Cl}_{2}\) (gas) to cleave homolytically, to produce two chlorine radicals, rather than heterolytically, to produce \(\mathrm{Cl}^{+}\) and \(\mathrm{Cl}^{-}\).

Short Answer

Expert verified
Ultraviolet light provides sufficient energy to break the weak bond between the two chlorine atoms in the Cl2 molecule. Homolytic cleavage is favored over heterolytic cleavage because the energy cost of separating charges in the gas phase is comparatively high, and chlorine atoms are more stable in their radical form than in their ionic form. Hence, ultraviolet light causes Cl2 gas to cleave homolytically, producing two chlorine radicals.

Step by step solution

01

Understanding homolytic and heterolytic cleavage

Homolytic cleavage is when a chemical bond breaks, and each of the two resulting fragments retains one electron from the bond. This produces free radicals, which have unpaired electrons and are highly reactive. In contrast, heterolytic cleavage occurs when one fragment retains both electrons from the bond, creating a negatively charged ion, and the other fragment becomes a positively charged ion.
02

Considering the chlorine molecule

Chlorine is a diatomic molecule, consisting of two chlorine atoms covalently bonded together by sharing an electron pair. The bond between the two chlorine atoms is relatively weak, making it more susceptible to cleavage when exposed to energy.
03

Understanding the energy of ultraviolet light

Ultraviolet light has a higher energy than visible light. When a molecule absorbs this high-energy light, it gains enough energy to break its chemical bonds. In the case of Cl2, the absorbed energy enables the bond between the two chlorine atoms to break.
04

Comparing the stability of the products

Upon bond cleavage, there are two possible outcomes: homolytic cleavage, producing two chlorine radicals, or heterolytic cleavage, producing Cl+ and Cl-. The latter requires separating the charges, creating a positive and a negative ion. This process is less favorable due to the energy cost of separating charges in gas phase and due to the fact that the single unpaired electron in chlorine atom is less stable in an ionic form than in a radical form.
05

The reason for homolytic cleavage in Cl2

The energy provided by ultraviolet light is sufficient to break the relatively weak bond between the two chlorine atoms in the Cl2 molecule. When the bond breaks, homolytic cleavage is favored over heterolytic cleavage because the energy cost of separating charges in the gas phase is comparatively high. In addition, chlorine atoms in their radical form are more stable than in their ionic form. Therefore, ultraviolet light causes Cl2 gas to cleave homolytically and produce two chlorine radicals.

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Most popular questions from this chapter

\(5.82 \mathrm{~g}\) of a compound was burned in the presence of oxygen. The products were \(17.1 \mathrm{~g}\) of carbon dioxide and \(10.5 \mathrm{~g}\) of water. Calculate the empirical formulas for this compound. What is its name? Find the percent yield of this reaction.

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