Is Chemical Equilibrium A Dynamic Equilibrium: 7 Facts


In this article, “is chemical equilibrium a dynamic equilibrium” the properties and basic differences of static and dynamic equilibrium with some relevant topics are discussed below.

Chemical equilibrium is a dynamic equilibrium in which the concentration of the reactant and product are always happening but the ratio of the reactant and product are constant. Any chemical reaction attains dynamic equilibrium condition when the rate or velocity of both the forward and backward reaction becomes equal.

Let’s focus on the following discussions below.

Is chemical equilibrium dynamic or static?

Chemical equilibrium is a physical state in which the rate of forward and backward reaction become equal. The rete of formation of product = the rate of dissociation of product. Thus, there is no any observable change in that reaction if it achieves equilibrium condition.

In chemical equilibrium, reaction is not stopped. The reactants are involved in product formation as well as the products are also involved in dissociation into reactants. So, there is no net change is observed. But the rate of both the reaction does not become zero, they are equal.

is chemical equilibrium a dynamic equilibrium
Amount of reactant (in red) decreases and amount of product increases (in blue).
Image Credit: Wikimedia Commons.

Now equilibrium can be classified into two categories. They are-

  1. Dynamic equilibrium
  2. Static equilibrium

Dynamic equilibrium is basically defined as one of the physical states of any reaction in which change of the rate of the forward and backward reaction or the change of the ratio of the reactant and product concentration is constant with respect to time. It is a particular example of steady state of any reaction.

Static equilibrium is the equilibrium, in which net mechanical change on a chemical reaction is zero no change of any parameters like concentration ratios, rate of the forward and backward reaction etc.

The characteristics of chemical equilibrium resembles with the properties of dynamic equilibrium. Thus, chemical equilibrium is a dynamic equilibrium instead of static equilibrium.

Why is chemical equilibrium a dynamic equilibrium?

At equilibrium, the concentration of each of the components (product and reactant) is constant. But the reaction is not stopped. Both the forward and backward reaction is going at the same time.

The reason behind this is that the rate of forward reaction (change of concentration with respect to time) is exactly equal to the rate of backward reaction. The formation of product and conversion of reactant from product is happening in equal rate. So, there is no change of concentration of either product or reactant.

Such condition is known as dynamic equilibrium in chemistry.

When is chemical equilibrium a dynamic equilibrium?

Chemical equilibrium occurs when the concentration of both the product and reactant sides become equal. Reactant converts into product after certain chemical changes. At the starting of any chemical reaction, the rate of forward reaction (conversion of product from reactant) is very much greater than the backward reaction (conversion of reactant from product). Because rate depends upon the concentration of reactant concentration. At the previous stage, the concentration of reactant is very much greater than the product concentration.

But with the progress of the reaction, the concentration of product is increasing gradually and the reverse reaction that is the formation of reactant from product is also started. After a certain time both the reaction rate will be same and the chemical equilibrium is achieved.

After attaining the equilibrium. The reaction will not be stopped. Both the reaction is proceeding towards both the forward and backward direction but no change is observed as both of the rate is same.

Why chemical equilibrium is not a static equilibrium?

Basically, chemical equilibrium is such a resting state of any chemical reaction in which the changing of concentration of the reactant as well as product is stopped.  Static equilibrium is also known as mechanical equilibrium because the net mechanical force on this equilibrium is zero. Due to having no mechanical force, the reaction is stopped.

But in chemical equilibrium, the chemical reaction is not stopped. The reaction is in steady state which means both the reaction rate will become exactly same. So, when any chemical reaction reaches in the equilibrium stage, both the forward and backward reaction is proceeding but in a same rate.

Thus, chemical equilibrium cannot be a static equilibrium.

Difference Between Chemical Equilibrium and Dynamic Equilibrium

The key difference between chemical equilibrium and dynamic equilibrium is that chemical equilibrium defines a state in which the concentrations of reactant and product do not undergo any changes but the dynamic equilibrium describes that state in which the ratio of reactants and products does not change.

It means that concentration of both the reactant and product can be changed but the ratio between reactant and product should be same in the dynamic equilibrium condition. But when any reaction reaches in the chemical equilibrium stage, the concentration of the reactant and product should be same throughout the equilibrium condition.

Examples of Chemical Equilibrium as Dynamic Equilibrium

  1. Conversion of NO2 to N2O4

In this conversion, brown coloured NO2 is converted into colourless N2O4 gas.

  2 NO2 N2O4

This is a reversible reaction. With forward reaction of dimerization of NO2, N2O4 also dissociates and form NO2. Thus, the equilibrium position and condition is not disturbed. At the initial time, the formation of dimer is greater than the dissociation due to the greater concentration of NO2.

Chemical equilibrium as dynamic equilibrium.
Image Credit: Wikimedia Commons.
  • 2. Reaction between NO2 and CO

Another example of dynamic as well as chemical equilibrium is the reaction between nitrogen dioxide and carbon monoxide.

NO2 (g) + CO (g) ⇌ NO (g) + CO2 (g)

This is a reversible reaction nitrogen oxide (NO) and carbon dioxide also reacts and form nitrogen dioxide (NO2) and carbon monoxide (CO).

Conclusion

From the above article, it is concluded that the chemical equilibrium is a dynamic equilibrium as both the rate of forward and backward reaction becomes zero when the reaction reaches at equilibrium but the reaction will not be stopped at equilibrium.

Aditi Roy

Hi..I am Aditi Roy, I have completed my graduation from University of Calcutta and am pursuing M.Sc in Chemistry from Techno India University. My area of specialization is on Inorganic Chemistry.

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