Page 3 - Microsoft Word - Equilibrium State key notes

Characteristics of Equilibrium Constant Kp or Kc
1. It has definite value for every chemical reaction at a particular temperature.

2. The more is the value of Kc or Kp, the more is the extent of completion of reaction,
i.e., Kc < 1 indicates lesser concentration of products than reactants.
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3
K ≥ 10 shows completion of reaction and K ≤ 10 shows that the reaction does not
proceed at all.
3. When the reaction can be expressed as sum of two other reactions, the Kc of
overall reaction is equal to the product of equilibrium constants of individual
reactions.
4. The equilibrium constant is independent of initial concentrations of reactants.

5. Equilibrium constant is independent of presence of catalyst.

6. Kc for backward reaction is inverse of Kc for forward reaction.
n
7. If an equation is multiplied by n, the K becomes K , and if it is divided by m, the k
becomes √k.
m
8. In equilibrium constant expression if activities are used in places of molar
concentration, h becomes dimensionless.

Types of Equilibrium
Homogeneous Equilibrium
In homogeneous equilibrium, the reactants and products arc present in the same
phase or physical suite (gaseous or liquid).

2SO2(g) + O2(g) ⇔ 2SO3(g)
Heterogeneous Equilibrium
In heterogeneous equilibrium the reactants and products are present in two or more
physical states or phases.

3Fe(s) + 4H2O(g) ⇔ Fe3O4(s) + 4H2(g)
Reaction Quotient
For any reversible reaction at any stage other than equilibrium, the ratio of the molar
concentrations of the products to that of the reactants. where each concentration
term is raised to the power equal to the stoichiometric coefficient to the substance
concerned, is called the reaction quotient, Qc.
For a general reaction

aA + bB ⇔ cC + dD

which is not at equilibrium,

c
b
a
d
Qc = [C] + [D] / [A] [B]
If
(i) Qc > Kc, the value of Qc will tend to decrease to reach the value of Kc (towards
equilibrium) and the reaction will proceed in the reverse direction.
(ii) Qc < Kc it will lend to increase and the reaction will proceed in the forward
direction.