Chapter 17, Problem 23Q

Monochloroethane (C₂H₅Cl) can be produced by the direct reaction of ethane gas (C₂H₆) with chlorine gas or by the reaction of ethylene gas (C₂H₄) with hydrogen chloride gas. The second reaction gives almost a 100% yield of pure C₂H₅Cl at a rapid rate without catalysis. The first method requires light as an energy source or the reaction would not occur. Yet ∆G° for the first reaction is considerably more negative than ∆G° for the second reaction. Explain how this can be so.