The degree of dissociation is `0.4` at `400 K` and `1.0` atm for the gaseous reaction
`PCl_(5) hArr PCl_(3)+Cl_(2)`
assuming ideal behaviour of all gases, calculate the density of equilibrium mixture at `400 K` and `1.0` atm (relative atomic mass of P is `31.0` and of Cl is `35.5`).

Explanation

`{:(,PCl_(5),hArr,PCl_(3),+,Cl_(2)),("Initial mole",1,,0,,0),("Mole at equilibrium ",(1-0.4),,0.4,,0.4):}`
Total mole at equilibrium `=1-0.4+0.4+0.4=1.4`
`("Normal" m_(PCl_(5)))/("Observed" m_(PCl_(5)))=1+alpha=1.4`
`:. "Observed" m_(PCl_(5))=(208.5)/(1.4)`
From `PV=(w)/(m)RT` at equilibrium
`(w)/(V)=(Pm)/(RT)=(1xx208.5)/(1.4xx0.0821xx400)`
`=4.53g//litre`