Page 2 - Microsoft Word - Equilibrium State key notes

4. The equilibrium state remains unaffected by the presence of catalyst. Catalst
helps to attain the equilibrium state rapidly.

5. The observable physical properties of the process become constant.

Law of Mass Action:
Guldberg and Waage states that the rate of a chemical reaction is directly
proportional to the product of the active masses of the reacting substances.
For a general reaction,

where, kf and kb are rate constants.
In heterogeneous equilibrium, the active mass of pure solids and liquids are taken as

At equilibrium,

Rate of forward reaction = Rate of backward reaction

Kc is called the equilibrium constant.
Use of Partial Pressures Instead of Concentration
For gaseous reactions, partial pressures are conveniently used since at any fixed
temperature partial pressure is directly proportional to concentration. For a general
gaseous reaction,

Relation between Kc and Kc
where, Δng = moles of products – moles of reactants (gaseous only)
Relation between Kc and Kp for different types of reactions
(i) When Δng = 0, Kp = Kc
(ii) When Δng = +ve, Kp > Kc
(iii) When Δng = -ve, Kp < Kc
Units of Kp and Kc
(i) Unit of Kp = (atm) Δn g
-1 Δn
(ii) Unit of Kc = (mol L ) g