Question

write the expression of Kc for the gas phase reaction :PCL5=PCL3+ CL2 ??​

Answer 1

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form PCL8+CL3

Answer 2

Phosphorus pentachloride dissociates in gas phase to give PCl3 and Cl2. This is an example of gaseous homogeneous equilibrium. It can be represented as PCl5(g) -- > < -- PCl3(g) + Cl2(g)

Phosphorus pentachloride dissociates in gas phase to give PCl3 and Cl2. This is an example of gaseous homogeneous equilibrium. It can be represented as

PCl5(g) -- > < -- PCl3(g) + Cl2(g)

For this reaction ∆n=1 Kp=Kc(RT)

Let us consider that one mole of PCl5 is present initially in a vessel of volume V dm3. At equilibrium let x mole dissociates to give x mole of PCl3 and x mole of Cl2. The equilibrium concentrations of the components can be given as follows :

PCl5(g) PCl3(g) Cl2(g)

Initial number of moles 1 0 0

Number of moles reacted x - -

Number of moles at equilibrium 1-x x x

Equilibrium concentration 1-x/V x/V x/V

According to law of mass action,

Kc = [PCl3][Cl2] / [PCl5]

Substituting the values of equilibrium concentrations in the above equation we get, Kc = (x/V)(x/V) / (1-x)/V

= x2V/V2(1-x)

= x2/ (1-x)V