At 473K, equilibrium constant `K_(C)` for the decompositioni of phosphorus pentachloride, `PCl_(5)` is `8.3xx10^(-3)`. If the decomposition is depicted as:
`PCl_(5)(g)hArrPCl_(3)(g)+Cl_(2)(g)DeltaH=124.0 kJ "mol"^(-1)`
a. Write an expression of `K_(c)` for the reaction.
b. What is the value of `K_(c)` for the reverse reaction at the same temperature?
c. What would be effect on `K_(c)` if
(i) more `PCl_(5)` is added (ii) pressure is increased (iii) the temperature in increased.

Explanation

a. `K_(c)=([PCl_(3)][Cl_(2)])/([PCl_(5)])`
b. The value of `K_(c)` for the reverse reaction at the same temperature is the reciprocal of the `K_(c)` value of same reaction.
`:.K_(c)` for reverse reaction `=1/(8.3xx10^(-3))=120.48`
c. (i) If `PCl_(5)` is added equilibrium shifts in the forward direction but `K_(c)` does not change.
(ii) If pressure is increased equilibrium shift in the backward direction but `K_(c)` does not change.
(iii) The dissociation of `PCl_(5)` is endothermic reaction. So increase in temperatures causes more dissociation of `PCl_(5)`. So `K_(c)` value increases.