Importance of Equilibrium Constant:

The value of Kc varies depending on the response. Kc isn’t only a calculating constant. It affects both the direction and the extent of a chemical reaction.

1. Direction of Chemical Reaction:

Determining the direction of reversible reactions is crucial for process optimization. The reaction quotient, Qc, helps predict the reaction’s state at any given time using actual concentrations. By comparing Qc to Kc, informed decisions can be made for efficient production or adjustment of the reaction. Comparing Kc and Qc values predicts response direction. We have three categories:

If Qc = Kc, the actual product and reactant concentrations are equal to the equilibrium concentrations, and the system is stable.
If Qc < Kc then there is increase in product concentration for equilibrium. So the forward reaction occurs, forming additional products.
If Qc > Kc, there is decrease in product concentration & to achieve equilibria As, the process reverses, forming more reactants.

2. Extent of Chemical Reaction:

At a certain temperature, the extent of a reaction measured. The magnitude of an equilibrium constant can predict the scope of a chemical reaction. As magnitude may be very high, very low, or moderate, so can be Extent of chemical reaction.

Kc is very small:
Reactions with low Kc never finish. That is, maximum reactant concentration and minimum product concentration. These are called ‘reverse or backward responses F_2(g)⇌2F_(g) Kc =7.4 × 10^-13 at 227°C
Kc is very large:
Reactions with high values are virtually complete. That is, maximum product concentration and minimum reactant concentration. This type of reaction is known as ‘Forward reaction’.
2H_2(g) + O_2(g) ⇌ 2H₂O Kc = 2.4 x 10⁴⁷at 227°C
Kc neither very small nor very large:
Reactions which have moderate value of Kc are considered to be at equilibrium. The concentration of reactants and products is almost same. For example:
N₂O_4(g) ⇌ 2NO_2(g) Kc=0.36 at 25°C