Gibb's free energy (∆G) and Equilibrium constant (Kc):

The part f energy which is converted into usefull work called Gibb's free energy or Gibb's function.

 

Energy (H) = Useful work (G) + Non useful (TS)

We van not calculate absolute value of 'G' so we calculate change in Gibb's free energy. 

             ∆G = ∆H -∆TS

       ∆G = ∆H - (∆TS + T∆S). ......(1)

Standard Gibb's energy (∆G°) change at  standard condition is 1 bar  and 298 K

             ∆G° = ∆H° -∆TS°  .......(2) 

Relation between ∆G° and Equilibrium constant (K):

(2) For the equilibrium, PCl 5​ (g)⇌PCl 3​ (g)+Cl 2​ (g) at 298K, K=1.8×10 −7 .Calculate ΔG 0 for the reaction (R=8.314JK −1 mol −1 ).

(2) Equilibrium constant for the reaction given below is 2.0 × 10^-7 at 300 K. calculate standard Gibb's free energy change for the reaction PCl5 (g) --=--PCl3 (g) + Cl2 (g) also calculate standard entropy change if ∆H° = 28.40 Kj mole-1.

Factor's Affecting Equilibrium Constant

(1) Le-Chetelier'e principle

(i) Effect of change in  temperature

(ii) Effect of change in  concentration 

(iii) Effect of change of volume of container at equilibrium

(iv) Effect of change in pressure

(v) Effect of Catalyst at equilibrium

(vi) Effect of Addition of Inert gas

(a) At constant volume

(b) At constant pressure 

          [End of Chapter = ∆∆∆]