At `473 K`, equilibrium constant `K_(c )` for decomposition of phosphorus pentachloride, `PCl_(5)` is `8.3xx10^(-3)`. If decomposition is depicted as,
`PCl_(5)(g) hArr PCl_(3)(g)+Cl_(2)(g) Delta_(r)H^(Θ)=124.0 kJ mol^(-1)`
a. Write an expression for `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 the effect on `K_(c )` if
i. More `PCl_(5)` is added
ii. Pressure is increased
iii. The temperature is increased?

Answer

b) `120.48`

Explanation

(a) `K_(c) = ([PCl_(3(g))][Cl_(2(g))])/([PCl_(5(g))])`
(b) Value of Kc for the reverse reaction at the same temperature is:
`K'_(c) = 1/(K_(c))`
`= 1/(8.3 xx 10^(-3)) = 1.2048 xx 10^(2)`
`= 120-48`
(c) (i) Kc would remain the same because in this case, the temperature remains the same.
(ii) `K_(c)` is constant at constant temperature. Thus, in this case, `K_(c)` would not change.
(iii) In an endothermic reaction, the value of `K_(c)` increases with an increase in temperature. Since the given reaction in an endothermic reaction, the value of `K_(c)` will increase if the temperature is increased.