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+B⇋C+D
at equilibrium, the rate of the forward reaction (A+B→C+D) equals the rate of the reverse reaction (C+D→A+B)
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.
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.
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.
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