Explain the reactivity of halogens towards hydrogen. - Vidyadip

Question

Explain the reactivity of halogens towards hydrogen.

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Answer

All halogens react with hydrogen and form hydrogen halides HX where X = F, Cl, Br, I.

The affinity and reactivity decrease down the group from F to I.
(a) $H _2+ F _2 \xrightarrow{\text { dark }} 2 HF$
(b) $H _2+ Cl _2 \xrightarrow[\text { sunlight }]{\text { diffused }} 2 HCl$
(c) $H _2+ Br _2 \xrightarrow{\text { heat }} 2 HBr$
(d) $H _2+ I _2 \stackrel{\text { heat }}{\rightleftharpoons} 2 HI$

Property	$H F$	$HCl$	$HBr$	HI
Boiling point $( K )$	293	189	206	238
Melting point $( K )$	190	159	185	222
Bond length $( H - X ) pm$	$91.7$	$127.4$	$141.4$	$160.9$
Bond dissociation enthalpy $\left( kJ mol ^{-1}\right)$	574	432	136	295

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