Dynamic Equilibrium - Static and Dynamic Equilibrium

When the two opposing forces are operating simultaneously and independent of each other, two states (state 1 and state 2) are formed with the interchange between the two states. The states are said to be in dynamic equilibrium. A double-sided arrow represents the dynamic equilibrium ”A ⇌ B”.

Depending on the composition of the two states, two equilibriums, namely physical or chemical equilibrium are defined.

Table of Content

What is Dynamic Equilibrium?

Dynamic Equilibrium can be defined as the state of a given system in which the reversible reaction taking place in it stops changing the ratio of reactants and products, but there is a movement of substances between the reactants and the products. This movement occurs at an equal rate and there is no net change of the reactant and product ratio.

For these types of equilibria, the equilibrium constants are represented with the help of the rate constants for the forward and backward reactions. Systems maintaining a dynamic equilibrium are examples of systems in steady states.

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Difference Between Static and Dynamic Equilibrium

Static equilibrium refers to a condition where the reaction occurring in a system is completely halted and there exists no movement between the reactants and the products corresponding to the chemical reaction.

If the forces acting on an object cancel each other, in addition to the constancy of content and composition, no movement of the object takes place. This is static equilibrium.

The key differences between static and dynamic equilibrium are tabulated below.

Static vs Dynamic Equilibrium
Dynamic Equilibrium Static Equilibrium
This type of equilibrium is reversible in nature. This type of equilibrium is irreversible in nature.
This equilibrium implies that the reactants and the products are still participating in chemical reactions. There is no further chemical reaction in the system.
In dynamic equilibrium, the forward and the backward reaction rates are equal In static equilibrium, the forward and backward reaction rates are zero
It can only occur in closed systems It can occur in both open and closed systems

However, the resultant force acting on both of these types of equilibria in a system is zero. Generally, neither of these types of equilibrium display visible changes.

Examples of Dynamic Equilibrium

A few important examples of dynamic equilibrium in our everyday life are listed below.

  • A new bottle of an aerated drink has a specific value for the concentration of the carbon dioxide present in the liquid phase in it. When the bottle is opened and half of the drink is poured out of it, the liquid carbon dioxide is slowly converted into gaseous carbon dioxide until a new point of equilibrium is reached, and the rate of conversion of CO2 from gas to liquid is equal to the rate of conversion of CO2 from liquid to the gaseous phase.
  • The single-phase system in which acetic acid undergoes dissociation, leading to an acid-base equilibrium. This state of dynamic equilibrium can be described by the following reaction. CH3COOH ⇌ CH3COO + H+
  • In the gaseous phase can be observed in the dimerization of nitrogen dioxide. Reaction: 2NO2 ⇌ N2O4
  • Henry’s Law is applicable in the first example of dynamic equilibrium provided above, wherein the equilibrium concentration of carbon dioxide in the liquid phase is proportional to the partial pressure of the CO2 gas in the bottle.
  • Industrial synthesis of ammonia via Haber’s process. Reaction: N2 (g) + 3H2 (g) ⇌ 2NH3 (g).

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