Question

Vapour density of PCI, is 104.16 but when heated
to 230°C its vapour density is reduced to 62. The
degree of dissociation of PCl, at this temperature
will be :
(1) 6.8% (2) 68% (3) 46% (4) 64%​

Answer 1

2)68%

Explanation is in photo

Answer 2

The  degree of dissociation of PCl₅ at this temperature is 68 %.

Given-

• Vapor density of PCl₅ = 104.16
• Final temperature = 230 °C
• Vapor density at final temperature = 62

The reaction is

                        PCl₅     ↔         PCl₃        +      Cl₂

Initial                 C                        0                    0

At equilibrium   C(1-α)                Cα                  Cα

So total number of moles at equilibrium can be given as

= C (1 - α) + Cα + Cα = C (1+α)

For the reaction at equilibrium, Vapor density should be inversely proportional to the number of moles. So,

Total moles at equilibrium/Initial total moles = Vapor density at initial / Vapor density at equilibrium

By substituting the values we get

C (1 + α) /C = D/d

1 + α = D/d

α = D/d -1

Here D = 104.16 and d = 62

Therefore,

α = 104.16/62 - 1 = 68 %