Le Chatelier's Principle - SS2 Chemistry Lesson Note

Le Chatelier's Principle is a fundamental concept in chemistry that describes the behaviour of chemical systems at equilibrium when subjected to external influences or changes in conditions. Le Chatelier's Principle states that if a system at equilibrium is subjected to a change in conditions, the system will respond in a way that tends to counteract that change and restore equilibrium. The principle is based on the idea that chemical equilibrium is a dynamic balance between forward and reverse reactions. When the equilibrium is disturbed, the system will adjust its composition to minimise the effect of the change. Le Chatelier's Principle can be applied to changes in temperature, pressure (for gaseous reactions), concentration, and the addition or removal of a catalyst.

Changes in Temperature:

●     Increasing the temperature of an endothermic reaction (heat is a reactant) shifts the equilibrium toward the products to absorb the added heat.

●     Increasing the temperature of an exothermic reaction (heat is a product) shifts the equilibrium toward the reactants to remove the excess heat.

Changes in Pressure (for Gaseous Reactions):

●     Increasing the pressure by decreasing the volume favours the side of the reaction with fewer moles of gas.

●     Decreasing the pressure by increasing the volume favours the side of the reaction with more moles of gas.

Changes in Concentration:

●     Increasing the concentration of a reactant shifts the equilibrium toward the products to consume the added reactant.

●     Increasing the concentration of a product shifts the equilibrium toward the reactants to consume the excess product.

Addition or Removal of a Catalyst:

●     The addition or removal of a catalyst does not affect the position of equilibrium. However, it increases the rate at which equilibrium is achieved by providing an alternative reaction pathway with lower activation energy.

It's important to note that Le Chatelier's Principle describes the short-term response of a system to changes. The system will adjust until a new equilibrium is reached. The principle is widely applicable in various areas of chemistry, including industrial processes, chemical synthesis, and environmental science. It helps in predicting the effects of changes in reaction conditions and optimising reaction conditions to maximise desired products.

Understanding and applying Le Chatelier's Principle is crucial for manipulating chemical systems, achieving desired equilibrium compositions, and designing efficient chemical processes.