Question

Identify the equation that shows the reaction of ethane with chlorine in the presence of ultraviolet light.

• A. C_2H_6 + Cl_2 C_2H_6Cl_2
• B. C_2H_6 + Cl_2 C_2H_4Cl_2 + H_2
• C. C_2H_6 + Cl_2 C_2H_5Cl + HCl
• D. C_2H_6 + Cl_2 2CH_3Cl

Hint:

Substitution reactions are characteristic of saturated compounds, while addition reactions are characteristic of unsaturated compounds (alkenes/alkynes)!

Answer 1

The Correct Option is C

The reaction being asked is the photochemical chlorination of ethane, which occurs in the presence of ultraviolet (UV) light. This reaction is a type of halogenation that involves free radical substitution, where a hydrogen atom in ethane (C₂H₆) is replaced by a chlorine atom from chlorine gas (Cl₂). Here is the step-by-step explanation:

1. The reaction initiates with the homolytic cleavage of the chlorine molecule under UV light, forming two chlorine radicals: \(Cl_2 \xrightarrow{UV} 2 \cdot Cl\)
2. One of the chlorine radicals reacts with ethane, abstracting a hydrogen atom and resulting in the formation of ethyl radical and hydrochloric acid: \(C_2H_6 + \cdot Cl \rightarrow C_2H_5 \cdot + HCl\)
3. The ethyl radical then reacts with another chlorine molecule, forming chloroethane (C₂H₅Cl) and regenerating the chlorine radical for further propagation: \(C_2H_5 \cdot + Cl_2 \rightarrow C_2H_5Cl + \cdot Cl\)

Thus, the balanced chemical equation for the reaction of ethane with chlorine in the presence of ultraviolet light is:

\(C_2H_6 + Cl_2 \rightarrow C_2H_5Cl + HCl\)

This demonstrates that the correct reaction equation from the given options is: C₂H₆ + Cl₂ → C₂H₅Cl + HCl.

Stage	Reaction	Result
Initiation	\(Cl_2 \xrightarrow{UV} 2 \cdot Cl\)	Formation of chlorine radicals
Propagation	\(C_2H_6 + \cdot Cl \rightarrow C_2H_5 \cdot + HCl\)	Formation of ethyl radical and HCl
Propagation	\(C_2H_5 \cdot + Cl_2 \rightarrow C_2H_5Cl + \cdot Cl\)	Formation of chloroethane, chain continuation

This reaction illustrates the free radical mechanism, typical for the halogenation of alkanes in the presence of light or heat.