Points to Remember:
- Chemical equilibrium is a dynamic state where the rates of forward and reverse reactions are equal.
- Equilibrium is affected by changes in pressure, temperature, and concentration, following Le Chatelier’s principle.
- The effect of these changes depends on the stoichiometry of the reaction and whether it is exothermic or endothermic.
Introduction:
Chemical equilibrium is a fundamental concept in chemistry describing the state of a reversible reaction where the rate of the forward reaction equals the rate of the reverse reaction. This doesn’t mean the concentrations of reactants and products are equal, but rather that their concentrations remain constant over time. The system appears static, but at a microscopic level, both forward and reverse reactions continue to occur at the same rate. This dynamic equilibrium is crucial in understanding many chemical processes, including industrial synthesis and biological reactions. The position of equilibrium is described by the equilibrium constant (K), which is the ratio of product concentrations to reactant concentrations at equilibrium, each raised to the power of its stoichiometric coefficient.
Body:
Characteristics of Chemical Equilibrium:
- Dynamic Nature: Equilibrium is a dynamic state, not a static one. Both forward and reverse reactions continue to occur at equal rates.
- Constant Concentrations: At equilibrium, the concentrations of reactants and products remain constant over time.
- Reversible Reactions: Equilibrium is only possible for reversible reactions, those that can proceed in both forward and reverse directions.
- Closed System: Equilibrium is typically established in a closed system, where no matter is exchanged with the surroundings.
- Temperature Dependence: The equilibrium constant (K) is temperature-dependent; changes in temperature shift the equilibrium position.
Effect of Pressure, Temperature, and Concentration on Equilibrium:
Le Chatelier’s principle states that if a change of condition is applied to a system in equilibrium, the system will shift in a direction that relieves the stress.
(i) PClâ â PClâ + Clâ
This reaction is an example of a dissociation reaction. One mole of PClâ decomposes into one mole of PClâ and one mole of Clâ.
- Effect of Pressure: Increasing pressure shifts the equilibrium to the left (towards reactants), favoring the formation of PClâ . This is because the left side has fewer gas molecules. Decreasing pressure shifts the equilibrium to the right.
- Effect of Temperature: This reaction is endothermic (absorbs heat). Increasing temperature shifts the equilibrium to the right (towards products), favoring the dissociation of PClâ . Decreasing temperature shifts the equilibrium to the left.
- Effect of Concentration: Increasing the concentration of PClâ shifts the equilibrium to the right. Increasing the concentration of PClâ or Clâ shifts the equilibrium to the left.
(ii) 2SOâ + Oâ â 2SOâ
This reaction is the industrial synthesis of sulfur trioxide, a crucial step in sulfuric acid production.
- Effect of Pressure: Increasing pressure shifts the equilibrium to the right (towards products), favoring the formation of SOâ. This is because the left side has more gas molecules (3) than the right side (2). Decreasing pressure shifts the equilibrium to the left.
- Effect of Temperature: This reaction is exothermic (releases heat). Increasing temperature shifts the equilibrium to the left (towards reactants), decreasing the yield of SOâ. Decreasing temperature shifts the equilibrium to the right.
- Effect of Concentration: Increasing the concentration of SOâ or Oâ shifts the equilibrium to the right. Increasing the concentration of SOâ shifts the equilibrium to the left.
Conclusion:
Chemical equilibrium is a dynamic state characterized by constant reactant and product concentrations and equal forward and reverse reaction rates. Le Chatelier’s principle effectively predicts the response of an equilibrium system to changes in pressure, temperature, and concentration. For reactions like the dissociation of PClâ , pressure changes significantly affect the equilibrium position, while for reactions like
the synthesis of SOâ, both pressure and temperature play crucial roles in optimizing product yield. In industrial processes, understanding and manipulating these factors are essential for maximizing efficiency and minimizing waste. Further research into catalyst development and process optimization can lead to more sustainable and environmentally friendly chemical production, aligning with principles of holistic development and resource conservation. CGPCS Notes brings Prelims and Mains programs for CGPCS Prelims and CGPCS Mains Exam preparation. Various Programs initiated by CGPCS Notes are as follows:-