Question

Monochloroethane (${\mathit{C}}_{\mathbf{2}}{\mathit{H}}_{\mathbf{5}}\mathit{C}\mathit{l}$) can be produced by thedirect reaction of ethane gas (${\mathit{C}}_{\mathbf{2}}{\mathit{H}}_{\mathbf{6}}$) with chlorine gas orby the reaction of ethylene gas (${\mathit{C}}_{\mathbf{2}}{\mathit{H}}_{\mathbf{4}}$) with hydrogenchloride gas. The second reaction gives almost a 100%yield of pure ${\mathit{C}}_{\mathbf{2}}{\mathit{H}}_{\mathbf{5}}\mathit{C}\mathit{l}$at a rapid rate without catalysis.The first method requires light as an energy source orthe reaction would not occur. Yet$\mathit{\Delta }{\mathit{G}}^{\mathbf{o}}$ for the first reaction is considerably more negative than$\mathit{\Delta }{\mathit{G}}^{\mathbf{o}}$ for thesecond reaction. Explain how this can be so.

Short answer

For kinetic reasons, the first reaction requires a light source. The first reaction takes a long timeif a light source is present. The thermodynamics of a reaction does not affect its kinetics. Even if the first reaction has a better thermodynamic advantage, it has a worse kinetic advantage. The second reaction is fast and unpleasant. When determining whether or not a reaction will occur, both kinetics and thermodynamics must be taken into account.

Step-by-step solution

Step 1: Explanation for chloromethane manufacture

Themanufacture of chloromethane is described using two ways. The first approach involvesproducing chloroethane by reacting ethane gas directly withchlorine gas, whereasthe second method requires reacting ethylene gas with hydrogen chloride gas. The second reaction yield is estimated to be almost 100%.

Explanation for first and second reaction

Thefirst reaction necessitates theuse of a light source for kinetic reasons. If a light source is present, the first reaction takes a long time to occur. The kinetics of a reaction is unaffected by the reaction's thermodynamics. Even if the first reaction is more advantageous in terms of thermodynamics, it is unfavorable in terms of kinetics. Thesecond reaction israpid and has a negativevalue. Bothkinetics and thermodynamics must be considered when determining whether or not a reaction will occur.