Factors Affecting Equilibrium - SS3 Chemistry Lesson Note
Chemical equilibrium is influenced by several factors that can shift the position of the equilibrium and affect the concentrations of reactants and products. Understanding these factors is crucial for manipulating chemical reactions to optimise yields and achieve desired outcomes.
Concentration of Reactants and Products:
The concentrations of reactants and products directly influence the position of the equilibrium. According to Le Chatelier's Principle, if the concentration of a reactant is increased, the equilibrium will shift in the direction of the products to consume the excess reactant. Conversely, if the concentration of a product is increased, the equilibrium will shift in the direction of the reactants to reduce the excess product. Decreasing the concentration of a reactant or product will cause the equilibrium to shift in the opposite direction.
Pressure (for Gaseous Reactions):
For gaseous reactions, the pressure can significantly affect the equilibrium position if the number of moles of gas changes during the reaction. If the pressure is increased, the equilibrium will shift in the direction that reduces the total number of moles of gas to counteract the increase in pressure. Conversely, if the pressure is decreased, the equilibrium will shift in the direction that increases the total number of moles of gas to compensate for the decrease in pressure.
Temperature:
The temperature has a profound effect on the position of the equilibrium and the equilibrium constant (K) for a reaction. The impact of temperature varies depending on whether the reaction is exothermic or endothermic:
● Exothermic Reactions: In exothermic reactions (where heat is a product), increasing the temperature will shift the equilibrium in the direction of the reactants. Decreasing the temperature will shift the equilibrium in the direction of the products. The equilibrium constant (K) for exothermic reactions decreases with increasing temperature.
● Endothermic Reactions: In endothermic reactions (where heat is a reactant), increasing the temperature will shift the equilibrium in the direction of the products. Decreasing the temperature will shift the equilibrium in the direction of the reactants. The equilibrium constant (K) for endothermic reactions increases with increasing temperature.
Catalysts:
Catalysts do not affect the position of the equilibrium but can influence the rate at which equilibrium is achieved. Catalysts provide an alternative reaction pathway with lower activation energy, allowing the reaction to reach equilibrium faster. They increase the rates of both the forward and reverse reactions equally, resulting in no net change in the concentrations of reactants and products at equilibrium.
Inert Gases:
The addition of inert gases (gases that do not react with the species in the equilibrium) does not affect the position of the equilibrium in a gaseous reaction. This is because the concentration of the species involved in the equilibrium does not change when inert gases are added, as they do not participate in the reaction.
Volume and Container Size:
For reactions involving gases, changes in volume or container size can affect the concentration of gases and, consequently, the position of the equilibrium. If the volume of the container is decreased, the pressure will increase, and the equilibrium will shift to the side with fewer moles of gas. Conversely, if the volume is increased, the pressure will decrease, and the equilibrium will shift to the side with more moles of gas.
Understanding how these factors affect chemical equilibrium is essential for predicting and manipulating reactions to achieve desired outcomes in various chemical processes and industries. By controlling these factors, chemists can optimise reaction conditions and maximise yields of products in a wide range of applications, including pharmaceuticals, petrochemicals, and environmental processes.