Equilibrium in Chemical Processes: Dynamic Equilibrium

Equilibrium plays basic role in chemistry, how reactions proceed and stabilise under given conditions. There are many types of equilibrium and dynamic equilibrium is one among them. It is having unique importance in chemical systems where reactions occur simultaneously and continuously, even though with no net change in the system’s macroscopic properties.

Chemical Equilibrium

Chemical equilibrium is a state of chemical reaction, where the concentrations of reactants and products remain constant over time. This does not mean that the reaction has ceased; in spite of this the forward and reverse reactions occur at the same rate.
There is no observable change in the system. Such a balance is dynamic in nature, as the processes continue at the molecular level even in the equilibrium state. For example, in the reaction:  A+BC+D
at equilibrium, the rate of the forward reaction (A+B→C+D) equals the rate of the reverse reaction (C+D→A+B)
Equilibrium in Chemical Processes: Dynamic Equilibrium-chemical reaction
Chemical reaction

Dynamic Equilibrium in Closed Systems

Dynamic equilibrium can only occur in closed systems where no matter is lost or gained, ensuring that the reactants and products are retained within the system. E.g., consider the reaction between hydrogen and iodine to form hydrogen iodide:  H2(g) + I2(g) 2HI(g).
When this reaction reaches equilibrium in a sealed container, both the forward and reverse reactions continue at an identical rate. The concentrations of H2​, I2​, and HI remain constant, though molecular collisions and reaction processes continue.
Equilibrium in Chemical Processes: Dynamic Equilibrium-Dynamic equilibrium
Dynamic equilibrium

Features of Dynamic Equilibrium

1.Reversible Nature: Dynamic equilibrium occurs in reversible reactions where the products can revert to reactants.
2. Steady-State Concentrations: The concentrations of reactants and products remain unchanged at equilibrium, though the reactions are still active.
3. Equal Reaction Rates: The rate of the forward reaction equals the rate of the reverse reaction.
4. Constant Macroscopic Properties: Observable properties such as pressure, colour, and concentration remain constant at equilibrium.

Role of the Equilibrium Constant (Keq​)

The equilibrium constant quantitatively describes the position of equilibrium. For a general reaction:  aA + bB cC + dD,
the equilibrium constant is expressed as:  Keq = [C]c[D]d / [A]a[B]b.
The value of Keq​  indicates whether reactants or products dominate at equilibrium:
  • Keq >1: Products are favored.
  • Keq <1: Reactants are favored.

Factors Affecting Dynamic Equilibrium

Dynamic equilibrium is sensitive to changes in conditions. Le Chatelier’s Principle provides a structure for predicting how a system at equilibrium responds to such changes.
1.Concentration: Increasing the concentration of a reactant or product shifts the equilibrium to counteract the change.
2.Temperature: A change in temperature can favour either the forward or reverse reaction, depending on the reaction’s enthalpy.
3.Pressure: For reactions like gases, changes in pressure affect equilibrium. Increasing pressure favours the side with fewer gas molecules.
4. Catalysts: Catalysts speed up both the forward and reverse reactions equally, helping the system reach equilibrium faster without altering the equilibrium position.
Catalysts

Applications of Dynamic Equilibrium

Dynamic equilibrium have wide applications in various fields:
1.Industrial Processes:
    • The Haber process for ammonia synthesis (N2 + 3H2 ⇋ 2NH3​) relies on optimising equilibrium conditions to maximise ammonia production.
    • The Contact process for sulfuric acid production (2SO2 + O2 ⇋ 2SO3​) is another example.
2.Biological Systems: Equilibrium plays a role in biological processes such as oxygen transport by hemoglobin, where the equilibrium between oxyhemoglobin and deoxyhemoglobin regulates oxygen delivery.
3.Environmental Systems: Dynamic equilibrium governs the carbon dioxide exchange between the atmosphere and oceans. Its control global climate patterns.

Importance of Dynamic Equilibrium

Dynamic equilibrium explain the behaviour of chemical systems under various conditions. It enables chemists to predict reaction outcomes, optimise industrial processes, and understand natural phenomena. Its dynamic nature also highlights the ever-present activity at the molecular level, its provide the complex balance of chemical processes.

Key points :-

  • If the process involves only chemical change, the equilibrium is called chemical equilibrium.
  • It is dynamic in nature.
  • The observable properties of the system become constant at equilibrium and remain unchanged.
  • The equilibrium can be approached from either directions.
  • The equilibrium can be attained only if the system is a closed one.
  • The free energy change at constant pressure and temperature is zero.
  • Addition of catalyst does not change the equilibrium state; it only helps in attaining the equilibrium faster.

Note :-

Dynamic equilibrium is a keystone concept in chemistry, bridging theoretical understanding with practical applications. On its principles and behaviour, scientists and engineers can connect its potential to develop innovative solutions in industrial, biological, and environmental background.
Dynamic equilibrium occurs in reversible chemical reactions when the forward and reverse reactions proceed at equal rates. As a result, the concentrations of reactants and products remain constant over time, even though molecular interactions continue.
In dynamic equilibrium, reactions are continuously occurring in both forward and reverse directions, maintaining constant concentrations. In static equilibrium, no reaction or movement occurs, and the system is at rest without ongoing processes.
System must be closed, meaning no matter can enter or leave, and the reaction must be reversible. Additionally, the reaction must be allowed sufficient time to reach equilibrium.
Equilibrium constant quantifies the ratio of product concentrations to reactant concentrations at equilibrium, raised to their respective stoichiometric coefficients. It indicates whether reactants or products are favored in the equilibrium state.
Le Chatelier’s Principle predicts how a system at equilibrium responds to changes in concentration, temperature, or pressure. The system adjusts to counteract the disturbance and restore equilibrium, shifting the position of the equilibrium as necessary.
No, a catalyst does not affect the equilibrium position. It only increases the rate at which equilibrium is achieved by speeding up both the forward and reverse reactions equally.
No, dynamic equilibrium can only occur in closed systems where reactants and products are retained, preventing loss or gain of matter that would disturb the equilibrium state.

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