3. A mixture of hydrogen and chlorine remains unreacted until it is exposed to u

Question

3. A mixture of hydrogen and chlorine remains unreacted until it is exposed to ultraviolet light from a burning magnesium strip. Then the following reaction occurs very rapidly. H2(g) + Cl2(g) 2HCI(g) G =-45.54 kJ AS--4.76 J/K Select the statement below that best explains this behavior. A) The reactants are thermodynamically more stable than the products. B) The reaction is spontaneous, but the reactants are kinetically stable. C) The reaction has a small equilibrium constant D) The ultraviolet light raises the temperature of the system and makes the reaction more favorable. E) The negative value for AS slows down the reaction. ANS: B KEY: general chemistry | thermochemistry | thermodynamics PTS: 1 DIF: moderate TOP: 10.1

Explanation / Answer

The reaction is called as the phosensitive reaction. The hydrogen and chlorine are stable in their elemental forms. When they are exposed to light from the Mg strip, the Cl----Cl bond is broken due to the higher energy of the light than the bond strength and free radicals are formed. The reaction proceeds further due to collision of the molecules and the free radicals.

Therefore the answer is B

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