Question

Arrange the following in order of property indicated for each set.
(i) $H_{2}O,H_{2}S,H_{2}Se,H_{2}Te$-increasing acidic character
(ii) $HF,HCl,HBr,HI$ -decreasing bond enthalpy

Answer 1

(i)
$Acidicstrength\propto stabilityofconjugatebase$
With the increasing size of the anion, the negative charge is more stable on a large anion beacuse of the diffusion of charge.
The given acids are hydrides of 16th group and going down the group, the size of the atoms increases and thus the order of acidic strength of the hydrides are:
$H_{2}O<H_{2}S<H_{2}Se<H_{2}Te$

(ii)
$Bondenthalpy\propto \frac{1}{bondlength}$
The decreasing order of bond enthalpy is:
$HF>HCl>HBr>HI$