Factors Affecting Equilibrium in Reversible Reactions:
1. Concentration:
● Increasing the concentration of reactants shifts the equilibrium position in the direction of the products, favouring the forward reaction to consume the added reactants.
● Increasing the concentration of products shifts the equilibrium position towards the reactants, favouring the reverse reaction to consume the excess products.
Example: Consider the reaction N2(g) + 3H2(g) ⇌ 2NH3(g). Adding more N2 will shift the equilibrium to the right, favouring the formation of NH3.
2. Pressure (for Gaseous Reactions):
● Changing the pressure only affects the equilibrium position for reactions involving gaseous species.
● Increasing pressure shifts the equilibrium towards the side with fewer moles of gas to reduce the pressure, while decreasing pressure shifts the equilibrium towards the side with more moles of gas to increase the pressure.
Example: For the reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), increasing the pressure will favour the formation of SO3, as it reduces the volume by decreasing the number of moles of gas.
3. Temperature:
● Increasing temperature favours the endothermic reaction (absorbs heat) and shifts the equilibrium position in the direction of reactants.
● Decreasing temperature favours the exothermic reaction (releases heat) and shifts the equilibrium position towards products.
Example: For the reaction N2(g) + O2(g) ⇌ 2NO(g) + heat, increasing the temperature will shift the equilibrium to the left, favouring the reactants as the reaction is endothermic.
4. Catalysts:
● Catalysts have no impact on the equilibrium position, but they increase the rate at which equilibrium is reached by accelerating both the forward and reverse reactions.
● A catalyst enhances the establishment of equilibrium but does not alter the equilibrium concentrations of reactants and products.
Example: In the Haber-Bosch process for ammonia production, iron is used as a catalyst to speed up the reaction N2(g) + 3H2(g) ⇌ 2NH3(g), improving the efficiency of ammonia synthesis.
Real-World Examples:
1. Haber-Bosch Process: In the industrial production of ammonia using the Haber-Bosch process, the reaction N2(g) + 3H2(g) ⇌ 2NH3(g) is achieved by optimising reaction conditions. The process involves maintaining high pressure to favour ammonia formation and using an iron catalyst to speed up the reaction rate, thereby increasing the yield of ammonia.
2. Equilibrium in the Atmosphere: The reaction of nitrogen oxides (NOx) in the atmosphere plays a role in forming smog and acid rain. The presence of sunlight promotes the formation of nitrogen dioxide (NO2) from nitrogen monoxide (NO). However, temperature and pressure changes in the atmosphere may influence the equilibrium between NO and NO2, impacting air quality.
In conclusion, chemical equilibrium in reversible reactions is influenced by various factors such as concentration, pressure (for gaseous reactions), temperature, and the presence of catalysts. Understanding how these factors affect the equilibrium position is crucial in industrial processes, environmental studies, and various applications in chemistry. Proper manipulation of these factors can be utilised to optimise reaction conditions and enhance the efficiency of chemical processes.