1.

4.5 g of PCl5 on vapourisation occupied a volume of 1700 mL at 1 atmosphere pressure and 227 °C temperature. Its degree of dissociation is

Answer»

0.0921
0.0091
0.921
None of these

Solution :Let the degree of dissociation be `alpha`, then
`PCl_(5)toPCl_(3)+Cl_(2)`
`(1-alpha)""alpha""alpha`
(M) Molecular weight of `PCl_(5)` = 31 + 5 `xx` 35.5 = 208.5
Total number of MOLECULES before dissociation= 1
Total number of molecules after dissociation
`=1-alpha+alpha+alpha=1+alpha`
THUS each gram mole changes to (1 + a) gram-mole.
Thus `PV=W/M(1+alpha)RT`
( V = volume after dissociation)
or `1xx1700/1000=(4.5)/(208.5)(1+alpha)RT` [1700ml`=1700/1000L`]
or `alpha=0.921`
`therefore%` age dissociation =92.1%


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