At `473 K`, partially dissociated vapours of `PCl_(5)` are `62` times as heavy as `H_(2)`. Calculate the degree of dissociation of `PCl_(5)`.

Answer

A, D

Explanation

`{:(,PCl_(5),hArr,PCl_(3),+,Cl_(2)),("moles before",1,,0,,0),("dissociation",,,,,),("moles after",1-alpha,,alpha,,alpha),("dissociation",,,,,):}`
Since, `(1)/("Normal" Mw) prop` Particles before dissociation
`(1)/("Exp." Mw) prop` Particle after dissociation
`:. ("Normal" Mw)/("Exp." Mw)=("Particles after dissociation")/("Particles before dissociation")=1+alpha`
`:'` Exp. Mw`=62xx` molecular weight of `H_(2)=62xx2`
`2085/(62xx2)=1+alpha`
`:. alpha=0.6814` or `68.14%`