Write the equilibrium constant expression for PCI; decomposition.
Answers
Answer:
The dissociation equilibrium of PCl
5
in gaseous state is written as PCl
5(g)
⇌PCl
3(g)
+Cl
2(g)
Let 'a' moles of PCl
5
vapour be present in V, liters initially. If x moles of PCl
5
dissociate to PCl
3
and Cl
2
gases at equilibrium then, the molar concentrations of PCl
5
, PCl
3
and l
2
gases at equilibrium will be
V
a−x
,
V
x
and
V
x
respectively.
∴K
c
=
[PCl
5
]
[PCl
3
][Cl
2
]
=
V
a−x
V
x
×
V
x
=
V
2
x
2
×
a−x
V
K
c
=
(a−x)V
x
2
x= degree of dissociation
x=
Totalnumberofmolespresentinitially
Numberofmolesdissociated
K
c
=
(1−x)V
x
2
[∵ initially the no. of PCl
5
present=1 mole ]
=
(1−x)RT
⋅x
2
P
[∵PV=RT]
In terms of partial pressure of PCl
5
,PCl
3
and Cl
2
, then
K
p
=
pPCl
5
pPCl
3
⋅pCl
2
atm
K
p
=
1−x
2
x
2
P
atm.