Dynamic Equilibrium

Equilibrium is defined as the state of a system during which the rate of forward reaction is equal to the rate of backward reaction. The number of moles of substrates in the reaction equals the number of moles of products at the equilibrium stage. A reaction may or may not be able to proceed in both forward and backward directions. However, if it is a reversible reaction, it tends to have a dynamic equilibrium condition.

Table of Contents:

Dynamic-Equilibrium
Examples-of-Dynamic-Equilibrium
Factors-Affecting-Dynamic-Equilibrium
Practice-Problems
Frequently-Asked-Questions

Dynamic Equilibrium

The condition is set to be present only in dynamic equilibrium if the net change in the reaction is zero. An equal amount of substrate is broken into products, and the equal amount of product converts into the substrate. The dynamic equilibrium depicts the scenario of no movement or no reaction occurrence. Yet, the reaction takes place at an equal rate in both directions. The system in dynamic equilibrium is referred to as a steady state.

Examples of Dynamic Equilibrium

A few of the numerous real-life examples are exhibiting dynamic equilibrium are as follows:

The half-filled soda bottle, after some time, has an equilibrium condition where the rate of conversion of carbon dioxide molecules into gas and liquid phase equals.
Filling the draining bathtub where the water exit rate equals the incoming water.
The reaction between hydrogen and hydroxyl ions where they combine to form water and degrade to form the reactants.
The ocean's salt concentration remains the same regardless of numerous phenomena occurring in the ocean. The rate of introduction from different water bodies equilibrates the rate of removal.
The reaction between oxygen molecules and their ions in the stratosphere is where they combine to form ozone and degrade to form the reactants.

Factors Affecting Dynamic Equilibrium

There are a few significant factors that control the dynamic equilibrium, such as:

Concentration

The change in concentration of the system at dynamic equilibrium can shift the equilibrium in a specific direction. According to Le Chatelier’s principle, the increase in reactant concentration will shift the equilibrium to the right, while the increase at the product side will shift the equilibrium towards the left.

Pressure

The change in pressure causes the equilibrium to shift. The higher pressure is accompanied by lesser moles of gas, while lower pressure favours the production of higher moles of gas.

Temperature

The change in temperature is coupled with a change in equilibrium constant according to the Van’t Hoff equation. In the case of exothermic reactions, the higher temperature shifts the equilibrium towards the left or reactants side, while a decrease in temperature favours the product formation. Alternatively, the endothermic reaction has a left shift for lower temperatures and a right shift for higher temperatures.

Catalysts

The catalysts neither alter the equilibrium of the reaction nor the concentration of products and reactants. However, they do play a role in increasing the rate of reaction leading to attaining an equilibrium state sooner.

Solvent Effects

The varying range of stability, solubility and interactions of reactants and products impact the equilibrium.

Presence of inert gases

The inert gases do not participate in the reaction but contribute to the concentration and pressure. It influences the direction of reaction according to Le Chatelier’s principle, as stated above.

Practice Problems

Q1. Which of these factors indicates the difference between static and dynamic equilibrium?

A. Direction of reaction
B. System of reaction
C. Both a and b
D. None of the above

Ans. C. Both a and b

The dynamic equilibrium is seen in reversible reactions occurring in closed systems. Static equilibrium concerns the irreversible nature of both open and closed systems.

Q2. Why is dynamic equilibrium possible in reversible reactions?

A. The forward reaction is faster than the backward reaction.
B. The backward reaction is faster than the forward reaction
C. The rate of forward reaction can be the same as the backward reaction
D. Dynamic equilibrium is possible in irreversible reactions.

Ans. C. The rate of forward reaction can be the same as the backward reaction

The dynamic equilibrium is the state of no net change which is possible when the rate of reaction in both directions is the same.

Q3. How does a closed system contribute to dynamic equilibrium?

A. By maintaining the same variables like concentration, temperature and pressure
B. By allowing change of variables by releasing them in the environment
C. By allowing change of variables by capturing them from the environment
D. Dynamic equilibrium is seen in open systems

Ans. A. By maintaining the same variables like concentration, temperature and pressure

The closed system eliminates the possibility of exchanging elements, thus maintaining the net contents of the system.

Frequently Asked Questions

Q1. What are the different laws associated with dynamic equilibrium?
Answer: Besides Le Chatelier’s principle, the law of mass action, equilibrium constant, Gibbs’ Phase rule and Boltzmann Distribution Law are also associated with dynamic equilibrium.

Q2. Can dynamic equilibrium be disturbed?
Answer: Yes, the dynamic equilibrium gets influenced and hence is disturbed by multiple factors listed above.

Q3. What is Henry’s law?
Answer: Henry’s law states the direct proportionality of gas solubility and partial pressure of that gas.