Question

For the reaction $C_2{H}_{5}OH+HX\to C_2{H}_{5}X+H_{2}O$, the order of reactivity is:

• A. $HCl>HBr>HI$
• B. $HI>HBr>HCl$
• C. $HBr>HCl>HI$
• D. $HI>HCl>HBr$

Answer 1

Answer: (B)

$HI>HBr>HCl$

The reaction $C_2{H}_{5}OH+HX\to C_2{H}_{5}X+H_2$ is a nucleophilic substitution reaction where the reactivity of $HX$ will depend upon the bond strength of $H-X$ bond and availability of the nucleophile i.e. $X^{-}$

Since $H-I$ bond strength (bond dissociation enthalpy) is the weakest and among halides, $I^{-}$ is the strongest nucleophile, thus reactivity for the reaction $C_2{H}_{5}OH+HX\to C_2{H}_{5}X+H_2$ will follow the order as:

$HI>HBr>HCl$