Dynamic Equilibrium

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Dynamic Equilibrium

If a system attains equilibrium or a reaction is said to be in equilibrium if and only if the rate of a forward and reverse reaction becomes equal. There are mainly two types of equilibrium existing: dynamic equilibrium and static equilibrium. For a dynamic equilibrium, the reaction occurs continuously and the rate will be equal and unchanged.

What is Dynamic equilibrium?

Consider a simple reaction of water

H2O(l) ⇌ H+(aq) + OH-(aq)

The symbol ⇌ shows that the reaction is in dynamic equilibrium. A steady-state system has always a dynamic equilibrium where there rate of reactant to covert products and products to covert reactants become equal and constant throughout.

Examples of Dynamic equilibrium

  1. A sealed bottle of soda can be taken as an example for this equilibrium. Soda present inside the bottle will be carbon dioxide which can be liquid or gaseous form. The two phases will be in equilibrium because when we pour some liquid soda it will be converted into gaseous carbon dioxide until its equilibrium is reached. Therefore the rate will be equal in both states of conversion.
  2. An acid-base equilibrium of dissociation of acetic acid is another example of the dynamic equilibrium. CH3COOH ⇌ CH3COO– + H+
  3. NaCl(s) ⇌ Na+(aq) + Cl-(aq). The dissociation of Sodium chloride is one example. The rate of dissolution is equal to the rate of crystallisation.

Differentiation of Dynamic equilibrium and Static equilibrium

Both of the equilibrium occurs in steady-state where the net force acting on the system becomes zero. But there is some difference between both types.

Dynamic Equilibrium


1.    This occurs in reversible reactions

2.    The reaction occurs continuously

3.    The rate of forward reaction is equal to the rate of the reverse reaction

4.    It occurs in closed systems

Static equilibrium


1.    This occurs in irreversible reactions

2.    The reaction has stopped and the movement is restricted between reactants and products.

3.    The rate of forward and backward reaction is zero

4.    It can occur in either closed or open system.


A mixture that includes two or more liquid phase which one is present as droplets are called emulsion. It consists of two immiscible liquids. One phase will be dispersed and another one will be mobile. To disperse two immiscible liquid a third component called an emulsifier is needed.

Types of Emulsion

There are mainly two types of emulsion: Oil in water and water in oil. According to the properties of dispersed medium and dispersed phase this has been classified.

  1. Oil in water (O/W)

In this type, the oil will be dispersed throughout the water. In other words here oil will be the dispersed phase and water will be the dispersed medium. Example of this type of emulsion is milk, mayonnaise etc.

  1. Water in oil (W/O)

The dispersed phase will be water and dispersed medium will be oil in this scenario.

It can be also referred to as an inverse emulsion. Example: Butter, cold cream etc.

To make W/O is more difficult than O/W.

Properties of Emulsion

  • The emulsion contains always a dispersed phase and a dispersed medium.
  • The third component of emulsifier or an emulsifying agent is required in an emulsion.
  • They are a highly stable system.
  • They consist of two immiscible liquids which can be prepared by continuous mixing.

Examples of Emulsions

There are examples according to the difference in the dispersed medium and dispersed phase.

  • Egg yolk containing emulsifying agent lecithin is an example of an emulsion
  • Crema on espresso comprises of water and oil as the dispersed phase and medium
  • Butter is an emulsion of water in fat
  • Mayonnaise is an oil in water emulsion

Uses of Emulsion

  1. It is used in cosmetics and other pharmaceutical applications.
  2. It is used in chemical synthesis
  3. Used in food products like butter, mayonnaise and margarine
  4. Used in making cold creams and also in firefighting


  • Dynamic equilibrium occurs in a reversible reaction where the reaction rate of both forward and backward reactions became equal.
  • A sealed bottle of soda is an example of this type of equilibrium
  • Dynamic and static equilibrium is different. Former is continuous and latter is stopped the reaction
  • An emulsion is a mixture of two immiscible liquid having a dispersed phase and medium
  • An everyday example is milk, butter and can be seen in the cold cream for dry skin which is a kind of emulsion.

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