6.2.4 The Effect of Changing Conditions on Equilibrium (HT only)

In a system at equilibrium, the relative amounts of all the reactants and products are determined by the conditions of the reaction. If any of the conditions are changed, the system responds in a way that counteracts the change and restores equilibrium. This phenomenon can be explained using Le Chatelier's Principle.

Le Chatelier's Principle

Le Chatelier's Principle states that if a system at equilibrium is subjected to a change in conditions, the equilibrium will shift in a direction that counteracts the change and establishes a new equilibrium.

Effects of Changing Conditions

• Concentration Changes: If the concentration of a reactant or product is increased, the equilibrium shifts in the direction that reduces the concentration. Conversely, if the concentration is decreased, the equilibrium shifts in the direction that increases the concentration.
• Pressure Changes (for gaseous reactions): If the pressure is increased, the equilibrium shifts in the direction that reduces the number of gas molecules. If the pressure is decreased, the equilibrium shifts in the direction that increases the number of gas molecules.
• Temperature Changes: The effect of temperature on equilibrium depends on whether the reaction is exothermicA reaction that releases heat, where the products have less energy than the reactants. or endothermicA reaction that ‘absorbs’ heat, where the products have greater energy than the reactants.. An increase in temperature favours the endothermic reaction, while a decrease in temperature favours the exothermic reaction.

Qualitative Predictions

Using Le Chatelier's Principle, it is possible to make qualitative predictions about the effect of changes on systems at equilibrium. By considering the changes in concentration, pressure, and temperature, we can anticipate the direction in which the equilibrium will shift.

Conclusion

Le Chatelier's Principle provides a qualitative understanding of the effects of changing conditions on equilibrium. It allows us to predict the direction of the equilibrium shift but does not provide quantitative information about the extent of the shift. By grasping the effect of changing conditions on equilibrium, we can understand how equilibrium systems behave and make informed predictions about the direction in which equilibrium will shift when subjected to various changes.