Question

At temperature i K, PCs is 50% dissociated at an equilibrium pressure of 4 atm. At what pressure it would
dissociate to the extent of 80% at the same temperature?
(1) 0.05 atm
(2) 0.60 atm
(3) 0.75 atm
(4) 2.50 atm​

Answer 1

Answer:

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At temperature T K,PCl

5

is 50% dissociated at an equilibrium pressure of 4 atm. At what pressure it would dissociate to the extent of 80% at the same temperature?

Medium

Solution

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Correct option is C)

PCl

5

⇌PCl

3

+Cl

2

(moles) Initial 1 0 0

At eqilibrium 1−x x x

Total no. of moles at eqm. =1−x+x+x=1+x

Partial pressure of a gas = mole fraction × total pressure

Partial pressure

1+x

1−x

P

1+x

x

P

1+x

x

P

K

p

=

P

PCl

5

P

PCl

3

×P

Cl

2

=

1+x

1−x

P

1+x

x

P

1+x

x

P

=

1−x

2

x

2

P

=

1−(0.5)

2

(0.5)

2

×4

=1.333(∵x=50% dissociation)

For 80% dissociation,

K

P

=

1−x

2

x

2

P

⇒1.33=

1−(0.8)

2

(0.8)

2

×P

∴P=0.75atm

Hence, the correct option is C.