Why is it preferable to produce chloroethane by the reaction of \(\mathrm{HCl}(g)\) with ethene than by the reaction of \(\mathrm{Cl}_{2}(g)\) with ethane? (See Exercise \(68 . )\)

We start by writing the chemical reactions for both methods: 1. HCl(g) with ethene (C₂H₄): \[C_2H_4 + HCl \rightarrow C_2H_5Cl\] 2. Cl₂(g) with ethane (C₂H₆): \[C_2H_6 + Cl_2 \rightarrow C_2H_5Cl + HCl\]

Next, we need to analyze the reaction mechanisms for both methods. 1. The reaction of HCl(g) with ethene proceeds via an electrophilic addition mechanism. HCl, being a strong electrophile, interacts with the double bond in ethene, leading to the formation of chloroethane. Since this mechanism is quite fast and efficient, only a small quantity of reactants is required to produce chloroethane. 2. The reaction of Cl₂(g) with ethane involves the radical substitution mechanism, which is less efficient. One chlorine atom removes a hydrogen atom from ethane, generating a free radical and HCl. The ethane radical then reacts with another chlorine molecule to form chloroethane. In this process, many side reactions may occur due to the presence of radicals leading to wasted reactants and product mixtures that need further separation for chloroethane purification, which means more reactants are required in comparison to the first method.

Now let's compare the environmental impacts of both methods: 1. The reaction between HCl(g) and ethene produces only one product, chloroethane. There are no toxic or harmful by-products generated during this process, which makes it environmentally friendly. 2. The reaction between Cl₂(g) and ethane generates chloroethane and HCl. Although HCl is a byproduct and can be used in some industrial applications, the increased consumption of chlorine gas, a highly toxic and harmful substance, makes this method less eco-friendly.

Considering the efficiency, reaction mechanism, and environmental impact, it is preferable to produce chloroethane by the reaction of HCl(g) with ethene. The electrophilic addition mechanism is faster and more efficient, requiring fewer reactants, and there are no harmful by-products generated during the process. In contrast, the reaction of Cl₂(g) with ethane is less efficient, generates toxic by-products, and requires more reactants for the same amount of chloroethane.