What is Le Chatelier's principle?

Le Chatelier's principle states that a system in equilibrium will adjust to counteract any change imposed upon it.

Le Chatelier's principle, named after the French chemist Henri Le Chatelier, is a fundamental concept in the study of chemical equilibria. It provides a way to predict the effect of changes in conditions on a chemical system at equilibrium. The principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change.

For instance, if you increase the concentration of reactants, the system will try to decrease it by making more products. Similarly, if you decrease the temperature, the system will try to increase it by favouring the exothermic reaction. This principle is applicable to changes in concentration, pressure, volume, and temperature.

Let's take an example. Consider the equilibrium between nitrogen dioxide (NO2) and dinitrogen tetroxide (N2O4) at room temperature:

2NO2(g) ⇌ N2O4(g)

In this reaction, NO2 is a brown gas and N2O4 is colourless. If we increase the pressure, the system will try to reduce it. It does this by favouring the reaction that produces fewer molecules, in this case, the forward reaction. As a result, the brown colour fades as more N2O4 is formed.

Le Chatelier's principle is not only a key part of IGCSE Chemistry but also a fundamental concept in real-world applications. It is used in industry to increase the yield of chemical reactions, by manipulating the conditions to favour the desired product. Understanding this principle can help you predict how a system will respond to changes, which is crucial in controlling chemical reactions.